Voacap Quick Guide Prelucrat v1541

1 VOACAP Quick Guide http://www.voacap.com/

What's New?          

Current International Smoothed Sunspot Numbers, Ri, to be used in VOACAP, from NOAA/NGDC (updated until 2018) Current Space Weather: Solar Wind, Magnetogram, X-Rays, Protons QTH Locator - find coordinates and Maidenhead locators on Google Maps How to Run VOACAP under Apple Macintosh OS X? - a quick guide to making text-based VOACAP predictions Elevation-Angle Analyzer - generate statistical elevation-angle data for HFTA o Statistical elevation-angle distribution - a case study Graphical Interface for VOACAP for Linux Rockwell Collins offers VOACAP 's Guide on CD-ROM for free (shipping charges apply) World Radio Broadcasting Stations - explore various BC transmitting sites on Google Maps My b Finnish: VOACAP, ennusteet ja antennit Sunrise and sunset times around the world o Today's Sunrise and Sunset Times by DXCC country o Today's Ionospheric Grayline by DXCC country o Today's Sunrise and Sunset at Global HF BC Transmitting Sites

1. ing VOACAP   

 

from Greg Hand's site, all new updates of the ITSHFBC package are available here Alternative direct , 8 Dec 2009 version (3.1 MB) from the home of VOACAP, NTIA/ITS, this ITSHFBC page has not been updated for long o The 8 Dec 2009 version o The 26 Mar 2009 version the Fortran source codes of the VOACAP Propagation Prediction Engine, in a special directory as ZIP files. VOACAP for Linux by J.A.Watson (M0DNS), an exciting project to make VOACAP available for Linux s. Please contribute! o Release 3 is out! the new VOACAP Linux GUI, Release 3!(1.5 MB gzipped file). Now s Area Coverage Maps with Jim Watson's VoaAreaPlot! This software is supplied 'as is' without any warranty, implied or otherwise. right-click and save the target. All s of Release 1 are strongly encouraged to upgrade, due to the bugs in R1. o VOACAP for Linux Software  The voacapl application: voacapl-0.5.7.tar.gz  The itshfbc directory: itshfbcFiles18Apr08.tar.gz  The python scripts to display the output

2. VOACAP - Backgrounds & Running the Prediction General       

VOACAP Overview Screenshots of VOACAP Modelling the real-life HF communication system into VOACAP Setting VOACAP input parameters Textual circuit prediction (Run > Circuit) Graphical circuit prediction (Run > Graph) Area coverage prediction (VOAAREA)

The calculation engine, VOACAPW  

An introduction to VOACAPW.EXE The FREQUENCY card in VOACAPX.DAT 1

Graphs & Colours   

VOACAP & VOAAREA contours VOACAP & VOAAREA plot colors Y-axis scaling for VOACAP Time & Distance graphs

3. VOACAP - Understanding the Prediction General      

Ten Common Mistakes in Using VOACAP Field Strength vs. Signal-to-Noise Choosing the correct Sunspot Number VOACAP Predictions at Low Frequencies Comparing VOACAP, ICEPAC and REC533 Method 25: Ionospheric Parameters and Semi-thickness

MUF, SNR and REL    

The MUF and SNR Distribution: Choosing the Best Frequency Understanding Above-the-MUF Predictions Calculating the MUFdays Maintaining the Required Grade of Service: Calculating the Circuit Reliability for a Given Hour

Signal Power & Noise Power  

Summing Signal Power from Multiple Modes Calculating the Received RF Noise Power

Antennas & Radiation Angles    

Method 15, or Transmitter & Receiver AntennaPatterns VOACAP Angle Predictions Minimum Angle in VOACAP Predicting the Takeoff Angle Parameter TANGLE

Conversions  

S DBW to S Meter Correlation Table The Z Tables

4. VOACAP - Case Studies  

VOACAP Case: Make your beacon predictions VOAAREA Case: RUV Gufunes

5. VOACAP-related Papers            

Using Propagation Predictions for HF DXing [2010] Visalia 2010 presentation by Dean Straw, N6BV. Contest Antennas. DX or Domestic, What’s Your Pleasure? [2009] Visalia 2009 presentation by Dean Straw, N6BV. What’s the Deal About “NVIS”?, [2005] article courtesy by Dean Straw, N6BV Another Way to View Propagation Predictions for DXing and Contesting [2006] Visalia 2006 presentation by Dean Straw, N6BV. In Search of the Ultima Thule. Can VOACAP Help Find the Ultimate QTH? [2006] CCF/OHDXF presentation by Jari Perkiömäki & George Lane. Improved Guidelines for Automatic Link Establishment Operations [2005] by George Lane o Graphs for the paper [2005] Review of the High Frequency Ionospheric Communications Enhanced Profile Analysis & Circuit (ICEPAC) Prediction Program [2005] by George Lane Required Signal-to-Interference Ratios for Shortwave Broadcasting, [7.2 MB] by George Lane, 1997 Predicting Signal-to-Interference Probability in the High Frequency Band, [60 kB] by George Lane and Greg Hand, 1997 Strategies Using Propagation Predictions for DXing and Contesting, by Dean Straw, N6BV What is VOACAP Trying to Tell Me? by Dean Straw, N6BV How Does VOACAP Compare With These Measurements, by Dean Straw, N6BV

6. NTIA/ITS HF software HELP Topics 

General information on the NTIA/ITS HF Propagation Analysis Package 2



   

VOACAP. General information - Point-to-Point - Area Coverage - Signal-to-Interference. Voice of America Coverage Analysis Program o VOACAP Frequently Asked Questions (22-Feb-96 Version) ICEPAC. General information - Point-to-Point - Area Coverage - Signal-to-Interference. Ionospheric Communications Enhanced Profile Analysis and Circuit Prediction Program REC533. General information - Point-to-Point - Area Coverage. ITU-RS Recommendation 533. This has been updated to the ITU 1996 Version 3. Data Files Frequently Asked Questions Helpful documents on using the propagation models o History (Part 1) of HF propagation models by Ray Rosich, 1978 o Introduction to the ICEPAC Technical Description o Excerpts from Original ICEPAC 's Manual o Corrections to Man-made Noise o Note on MUFDAYs o High Latitude Errors o Corrected Signal-to-Noise Ratio Distribution o A Comparison of Broadcast Quality to VOACAP using Methods 21, 22, and 30 o VOACAP Method 30. A Long Path/Short Path Smoothing Function

7. HamCAP 's Guide  

HamCAP v1.5 's Guide HamCAP and Type 13 & 14 Antennas

8. Articles of interest English   

The Woody Woodpecker Story, Part 3 [PDF, 115 kB] by V. K. Lehtoranta, OH2LX Jamming, or deliberate interference against radio broadcasting stations [PDF, 140 kB] by V. K. Lehtoranta, OH2LX www.radiojamming.info by Rimantas Pleikys

Finnish      

Kokeiluja Faroksella - automaattinen kelimajakoiden kuuluvuudenmittaus vs. keliennusteet Tee-se-itse täsmäennuste YLE Radio Finlandin lähetyksille VOACAP ennustaa kuuluvuuden signaali-kohinasuhteen avulla VOACAP taajuussuunnittelun työkaluna Avaruussään vaikutuksesta HF-keliin Avaruussään tarkkailua IonoProbella

Swedish 

VOACAP förutspår hörbarheten med hjälp av signal-noiseförhållandet

Japanese 

HamCAP 1.5 's Guide [PDF, 49 kB]

9. Tools & able files for use with VOACAP Find coordinates and Maidenhead grid locators just by pointing and clicking    

Browse the World with Google Maps, (start view: World) Browse the World with Google Maps, (start view: Scandinavia) World Radio Broadcasting Stations on Google Maps! new QTH Locator (Google Maps), updated!

ables Software    

MAKEVOA.EXE for creating VOACAP-compatible antenna models from HFTA, courtesy of R. Dean Straw N6BV (zipped, 34 kB) Elevation-Angle Analyzer for VOACAP, v1.0 Windows program (zipped, 830 kB) for conversion of on-line CTY.DAT to CTY.GEO [9 Dec 07]. Mac and Linux versions available upon request! Perl source code for conversion of WL_CTY.DAT to CTY.GEO

Coordinate files 3

Save the coordinate files (*.GEO) at C:\ITSHFBC\GEOCITY\      

New country coordinate list from CTY.DAT by AD1C. [9 Dec 07] GEO file for all Zones (WAZ). Courtesy of Peter Ackermann DL3NAA. Latest Global HF Transmitter Site List. [5 Aug 06] Latest country coordinate list by OH6BG. [30 Jul 06] Latest NCDXF beacon coordinate list [30 Jul 06] Finland city coordinate list

Antenna and configuration files     

A collection of antennas for use with VOACAP is available. If you wish to contribute, please let me know. Fine-tuned VOACAP Point-to-Point parameter auto scaling settings, English. Save as C:\ITSHFBC\DATABASE\Voacap.gph Fine-tuned VOACAP Point-to-Point parameter auto scaling settings, Finnish. Tallenna nimellä C:\ITSHFBC\DATABASE\Voacap.gph Fine-tuned Y-axis scaling for VOACAP Time & Distance graphs. Save as C:\ITSHFBC\DATABASE\voadist.gph Fine-tuned colors for auto-contour shading for Point-to-Point plots. Save as C:\ITSHFBC\DATABASE\Colors.gph

4

2 VOACAP - Backgrounds & Running the Prediction 2.1 General VOACAP Overview VOACAP is an improved and corrected version of IONCAP, retaining all of the theory as put forth by John Lloyd, George Haydon, Donald Lucas and Larry Teters in the 1975-1985 time-frame with modifications which were suggested/approved by George Lane, Donald Lucas,George Haydon and A. D. Spaulding (a world authority on HF radio noise predictions). Take a look at the VOACAP evolution chart (courtesy of George Lane, Lane Consultant). Major improvements in efficiency, coding corrections and ease of understanding the IONCAP program were made by Franklin Rhoads of the U.S. Navy Research Laboratory under the sponsorship of the Voice of America (1985-1996). Many of the newer features in VOACAP and VOAAREA were designed and implemented by Gregory Hand at the Institute for Telecommunication Sciences who created VOAAREA and made many significant improvements to VOACAP.     





 

   

VOACAP is the result of 50+ years of U.S. HF research and development Considered by many as the most professional HF system performance prediction tool available on the market Used currently for HF frequency planning by Voice of America and a number of other international HF broadcasters and institutions all over the world. Easy to use graphical interface and, for advanced s, powerful command line options Detailed Point-to-Point graphs and Area Coverage maps for 22 parameters of circuit quality such as o SNR (Signal-to-Noise Ratio) o Reliability o Required Power Gain o Signal Power o MUF o Takeoff/Arrival Angle, and more Accurate predictions of the distribution of Worldwide Atmospheric and Man-made radio noise using the latest ITU-R recommendations and a unique combination methodology developed by the late A. D. Spaulding, a world authority in the modeling of noise distributions Detailed hourly and 24-hour predictions for the entire HF spectrum [2 to 30 MHz] with assigned frequencies, such as o Point-to-Point Performance vs Distance at the given hour for the given parameter at one or all assigned frequencies o Point-to-Point Performance vs Time for the given parameter at one or all assigned frequencies on the 24-hour scale defined circuit databases for repeated or batch calculations Thirty calculation Methods for o ionograms o HPF-MUF-FOT o antenna patterns o complete system performance Versatile coverage maps: one transmitter to many receivers [VOAAREA], or many transmitters to one receiver [VOAAREA Inverse] for bi-directional circuit studies Freely adjustable geographical maps to be plotted on Adjustable precision in coverage map calculations Huge databases of more than 35,000 U.S. and world locations, including DXCC, NCDXF beacons, and HF broadcasting stations, to name a few 5

 

    

Accepts unlimited number of defined location databases Database of hundreds of transmit and receive antennas, with ability to adjustments using HFANT, for o amateur radio o broadcasting o SWL, and more Accepts unlimited number of defined antenna files (HFANT and Type 11 & 13) Comprehensive, -community ed online VOACAP Quick Guide available for beginners and advanced s FORTRAN source code freely available for the prediction module of VOACAP [VOACAPW] Not subject to copyright protection in the U.S. Available for free ing from the U.S. Department of Commerce (NTIA/Institute for Telecommunication Sciences; Boulder, Colorado).

Screenshots of VOACAP VOACAP (for point-to-point circuit analysis) and VOAAREA (for area coverage analysis) are extremely powerful tools for professional-grade HF circuit predictions. Contrary to the common belief, the VOACAP interface is often simpler than that of many other HF prediction software, and the result graphs and coverage maps usually outperform those of the competing tools. There is no competition, however, as VOACAP is free! Below you will catch a glimpse of the many exciting features VOACAP can offer.

2.1.2.1

The Input Screen

This is the input screen. Please note that there is only one screen, it cannot be much simpler than that.

2.1.2.2

HF Spectrum vs. Time Graphs-

This is the signal-to-noise (SNR) graph as a function of 2-30 MHz and time, for a circuit from the United Nations in NYC to Cape Verde in Africa. Besides this graph, there are 19 additional graphs that describe various properties of this particular circuit, such as signal power at receiver, and the optimum radiation angle of the transmitter antenna.

6

2.1.2.3

-defined Frequencies vs. Time Graphs

This is the 24-hour analysis graph of the given output parameter on -defined frequencies from the UN to Cape Verde, Africa. The can choose from 23 output parameters; shown here is the parameter SDBW, i.e. median signal power at receiver site. By looking at the graph, the can easily understand the behaviour of the lower frequencies and higher frequencies at the different times of the day on the given circuit.

2.1.2.4

-defined Frequencies vs. Distance Graphs

This is the distance graph of the given output parameter on -defined frequencies from the UN towards Cape Verde, Africa at 01 UTC. The distance graph shows how the -defined frequencies start to propagate away from the transmitter towards the receiver site. The can choose from 23 output parameters; shown here is again the parameter SDBW, i.e. median signal power at different distances from the transmitter. 7

2.1.2.5

Coverage Maps

Area coverage maps are perhaps the most exciting part of VOACAP. The coverage maps are made with the VOACAP companion program, VOAAREA. Coverage maps are produced by calculating a huge amount of point-to-point circuits from the transmitter to the geographical area defined by the . A 31x31 matrix, as shown here, means that the coverage map was created from 961 point-to-point circuit calculations. When the geographical area is large, a better resolution may be needed. VOAAREA allows a matrix of 361x361 (130,321 P-to-P circuits) to be calculated at maximum. This particular coverage map shows the median Maximum Usable Frequency from Finland to the rest of the world in November 2005 at 10 UTC. A total of 23 output parameters can be plotted on the map.

8

Modelling the real-life HF communication system into VOACAP 2.1.3.1

Overview of VOACAP input and output parameters

VOACAP operates in two visible modes, an input and output mode. The following two figures below give an overview of parameters that need to be taken into while constructing an HF communication system into a working VOACAP model.

Figure 1. Overview of VOACAP input parameters in relation to a real-life HF communication system.

Figure 2. Overview of VOACAP output parameters in relation to a real-life HF communication system. 9

Setting VOACAP input parameters After you have launched VOACAP, the first and most important thing is to select and enter right parameter values in the program. Here we discuss the most important steps. Below you will see the main screen with a set of reasonable input values for a high-power broadcasting station with transmissions to Southern Africa:

Figure 1. The VOACAP Main Screen

2.1.4.1

Basic Parameters

A Note about Coefficients As noted earlier, while using VOACAP or VOAAREA, be sure to select the CCIR coefficients. George Lane explains, "Do the URSI coefficients provide more accurate predictions? We do not know. What we do know is that original IONCAP using the CCIR data base, corrects the predicted values by using the Transmission Loss tables and determines the variability of the MUF values over the month using the F-tables. These are huge corrections. They are based on taking the predicted ionospheric calculations using the CCIR data and subtracting them from actual system performance data taken over the 1958 to 1963 time period. The differences are collected into the two sets of tables I just mentioned. The corrections are applied to any path prediction you make using IONCAP in order to predict signal power, SNR, reliability and required power gain. If you change the ionospheric maps for only the F-region and do not recalibrate the predictions against measurement, you do not know if you made an improvement or not. Chances are you have ruined the correlation." These are the basic settings which you can initially set up as follows:

10

Parameter Method

Recommendation Select Method Number 20 (Complete System Performance). If you are running circuits over 7000 km, use Method 30 (Short/Long Path Smoothing).

Year

This is a -specified value. It has no effect on calculations.

Coefficients Select CCIR (Oslo). This is the default for using VOACAP in long-term predictions. Do not use URSI88 (Australian). Time

Select UT (Universal Coordinated Time). Local Mean Time does not mean your local time but the local sun time at the receiver.

Transmitter Select the transmitter location from the pre-defined lists, sorted by city (worldwide), by nation (worldwide) and by state (USA). You can also enter the coordinates manually. Receiver

Select the receive location from the pre-defined lists, sorted by city (worldwide), by nation (worldwide) and by state (USA). You can also enter the coordinates manually.

Path

Select Short or Long Path. The default is Short Path.

Freq(MHz) Enter the frequencies to be used for calculation. Use the zero (0) value to remove a frequency from the set. A set of 11 -specified frequencies can be defined. Also three pre-defined frequency sets are available which can be modified if needed. Fprob

2.1.4.2

Do not use all default values. Set foE to 1, foF1 to 1, foF2 to 1 and foEs to 0 (zero, instead of 0.7).

Critical Parameters

The following are critical -specified parameters.

Groups

11

Parameter Months

SSNs

Recommendation Enter the number of the month (e.g. December = 12.00). You can specify a total of 10 months at a time. The format is MM.DD (month.day). VOACAP is not, however, suitable for daily predictions. Therefore, do not specify any day since if you do, the value of Coefficients will automatically be set to URSI88. Enter the monthly smoothed sunspot number for the given month.

Choosing the correct sunspot number (SSNs) There are a number of sunspot resources available on the Net. However, be sure to use the values from the following resource: 

Predicted Monthly Sunspot Numbers (from National Geophysical Data Center) ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SUNSPOT_NUMBERS/sunspot.predict

These are the current values for the year 2003 as of writing:

JAN 82.9

FEB 79.4

MAR 76.9

APR 74.3

MAY 71.2

JUNE JULY AUG 68.7 66.7 64.8

System

12

SEPT OCT 62.6 59.8

NOV 57.8

DEC 56.7

Parameter Man-made noise

Recommendation This is a critical setting. You can accept the default value of 145 (residential environment). If your receive location is in a quiet environment, you can use 155 or higher. There are still other values available, see the input help.

Min. take-off angle

If you are a radio amateur or SWL, enter the take-off value of 3. For better antenna installations, you can use the value of 1.

Req'd circuit reliability

Accept the default value of 90%.

Req'd SNR

This is a critical setting. For a reasonable BC listening quality, use 67. For a reasonable CW reception quality, use 24 (or 27) and for SSB, 45.

Multipath power tolerance

Accept the default value of 3 dB.

Max. tolerable Accept the default value of 0.10 milliseconds. time delay

Antennas Selecting the transmitter antenna

Parameter TxAnt=

Recommendation Select the transmitter antenna from the pre-defined lists. You must familiarise yourself with the available antenna patterns using HFant program, included in the VOACAP software package. This window is the place where you can 13

define different antennas for different frequency ranges. In the example above, we have defined one antenna for the frequency range of 2 MHz (Min) to 30 MHz (Max). MainBeam Enter the main beam of the antenna (in degrees). at Rx

Sets the main beam towards the receive location.

TxPower

The transmitter power which is fed to the antenna. Usually, we need to assume some power losses in transmission lines, etc. so you may set this value, for instance, to 65% of the transmitter power.

Selecting the receive antenna

Parameter

Recommendation

Receive Antenna=

Select the receive antenna from the pre-defined lists. You must familiarise yourself with the available antenna patterns using HFant program, included in the VOACAP software package. The default antenna SWWHIP.VOA represents a typical shortwave whip antenna.

Receiver bearing

If it is a directional antenna, enter the main beam in degrees. For nondirectional antennas, enter the value of 0.

at Tx

Sets the main beam towards the transmitter location.

Gain

This is valid only for isotropic antennas. The gain value is ignored if used with other antenna types.

14

Textual circuit prediction (Run > Circuit) 2.1.5.1

VOACAP output parameters

Below you will find brief definitions for the 22 parameters in the final column: Parameter MODE

Definition Ionospheric path for the most reliable mode (ie. the mode with the highest reliability of meeting the REQ.SNR). For the Short Path Model, the number of hops and mode type [E, F1, F2, Es layers] for the MRM are given, eg. 2F2. For the Long Path Model (not to be confused with the long path circuit!), the mode at the transmitter end and the mode at the receiver end are given, eg. F2F2 in our example above.

TANGLE Radiation angle for the MRM (degrees). RANGLE The angle at the receive end (for long path model only). DELAY Time delay for the MRM (milliseconds). V HITE

Virtual height of the MRM (kilometers).

MUFday

Fraction of days in the month at that hour that the operating frequency is below the MUF for the MRM.

LOSS

Median system loss for the MRM (dB).

DBU

Median field strength expected at the receiver location (dBu).

S DBW

Median signal power expected at the receiver input terminals (dBW).

N DBW

Median noise power expected at the receiver (dBW).

SNR

Median Signal-to-Noise ratio for power summation of all modes (dB-Hz).

RPWRG

Required combination of transmitter power and antenna gains (in dB) needed (+) or excess (-) to achieve the required reliability.

REL

Circuit reliability. Fraction of days per month for which the SNR equals to or exceeds the required SNR (REQ.SNR) at the given hour. In our example above, the REL of 0.78 at 11.9 MHz means that a 67-dB SNR or better can be maintained on 78% (ie. 23 days, see Z Tables) of days per month on 11.9 MHz at 0100 UT.

MPROB

Probability of an additional mode within the multi-path tolerances (short path only).

S PRB

Service probability. The probability that the required reliability will be met. Not completed, do not use.

SIG LW

Lower decile range for the signal power (dB).

SIG UP

Upper decile range for the signal power (dB).

SNR LW

Lower decile range for the SNR (dB).

SNR UP

Upper decile range for the SNR (dB).

TGAIN

Transmitter antenna gain at TANGLE (dBi).

RGAIN

Receiver antenna gain at TANGLE or RANGLE (dBi).

Signal-to-Noise ratio at the Required Reliability (REQ.REL.). Also known as SNR90, if the REQ.REL. is 90% (dB-Hz). After you have set all the circuit parameters in the VOACAP main screen, it is time to run the analysis. Choose Circuit from the Run menu (abbreviated later in these web pages as Run > Circuit). A new window will open, containing a lot of data. The data example below is the start of the prediction for the circuit of Pori (Finland) - Johannesburg (South Africa). SNRxx

15

IONOSPHERIC COMMUNICATIONS ANALYSIS AND PREDICTION PROGRAM VOACAP VERSION 01.1210W 1 2 3 4 5 6 7 123456789012345678901234567890123456789012345678901234567890123456789012345 COMMENT Any VOACAP default cards may be placed in the file: VOACAP.DEF LINEMAX 55 number of lines-per-page COEFFS CCIR TIME 1 24 1 1 MONTH 200112.00 SUNSPOT 110. LABEL YLE PORI JOHANNESBURG CIRCUIT 61.47N 21.58E 26.25S 28.00E S 0 SYSTEM 1. 145. 3.00 90. 67.010.00 0.05 FPROB 1.00 1.00 1.00 0.00 ANTENNA 1 1 2 30 0.000[hfcc\HFBC_218.P15 ]160.0 350.0000 ANTENNA 2 2 2 30 0.000[default\SWWHIP.VOA ] 0.0 0.0000 FREQUENCY 6.07 7.20 9.7011.8513.7015.3517.7321.6525.89 0.00 0.00 METHOD 30 0 EXECUTE QUIT CCIR Coefficients

~METHOD 30

VOACAP 01.1210W

PAGE

1

Dec 2001 SSN = 110. Minimum Angle= 3.000 degrees YLE PORI JOHANNESBURG AZIMUTHS N. MI. KM 61.47 N 21.58 E - 26.25 S 28.00 E 174.24 356.94 5275.6 9769.6 XMTR 2-30 REC705 #01[hfcc\HFBC_218.P15 ] Az=160.0 OFFaz= 14.2 350.000kW RCVR 2-30 2-D Table [default\SWWHIP.VOA ] Az= 0.0 OFFaz=356.9 3 MHz NOISE = -145.0 dBW REQ. REL = 90% REQ. SNR = 67.0 dB MULTIPATH POWER TOLERANCE = 10.0 dB MULTIPATH DELAY TOLERANCE = 0.050 ms 1.0 13.1 F2F2 4.0 12.0 34.4 360 0.50 142 44 -87 -167 80 13 0.74 0.00 0.35 25.0 17.7 26.7 18.5 19.7 -0.9 54

6.1 F2F2 7.6 7.6 34.2 290 1.00 146 35 -90 -153 63 16 0.24 0.00 0.19 9.7 4.9 12.4 7.6 21.9 -2.1 51

7.2 F2F2 7.8 7.8 34.2 297 0.99 143 39 -87 -156 69 12 0.57 0.00 0.28 11.2 4.9 13.8 7.1 21.9 -1.9 55

9.7 F2F2 3.3 3.3 33.9 314 0.95 142 48 -84 -162 78 10 0.74 0.64 0.34 19.2 6.2 21.2 7.8 18.3 -7.0 57

11.9 F2F2 4.0 12.0 34.3 332 0.73 138 47 -83 -165 83 11 0.78 0.00 0.38 25.0 11.6 26.7 12.7 19.7 -0.9 56

13.7 F2F2 4.0 12.0 34.6 387 0.38 145 41 -90 -168 78 16 0.70 0.00 0.33 25.0 21.5 26.8 22.2 19.7 -0.9 51

15.4 F2F2 7.8 22.0 35.2 466 0.12 157 29 -102 -169 68 26 0.51 0.00 0.23 25.0 25.0 26.8 25.7 21.8 0.0 41

17.7 F2F2 7.8 4.0 34.6 402 0.01 198 -5 -143 -171 28 66 0.03 0.00 0.03 25.0 25.0 26.8 25.7 21.8 -5.4 1

21.6 F2F2 7.8 8.0 35.5 574 0.00 268 -77 -212 -173 -39 133 0.00 0.00 0.00 25.0 25.0 26.8 25.7 21.8 -1.8 -66

25.9 F2F2 7.8 7.8 34.9 458 0.00 289 -96 -233 -176 -58 138 0.00 0.00 0.00 9.1 4.9 13.3 7.6 21.7 -1.9 -71

0.0 -

0.0 -

FREQ MODE TANGLE RANGLE DELAY V HITE MUFday LOSS DBU S DBW N DBW SNR RPWRG REL MPROB S PRB SIG LW SIG UP SNR LW SNR UP TGAIN RGAIN SNRxx

There are 24 blocks by hour in this example prediction. One hour block, as seen above out of 24, contains 14 columns. The first column is the time ("1.0") in UT (Universal Coordinated Time). Hours are centered on the hour. Thus, "1.0" represents the time from 0030 to 0130 UT centered at 0100 UT. The second column (the data under "13.1", ie. 13.1 MHz) is the predicted median maximum usable frequency (MUF) at that hour. Then follows the 11 -specified frequency columns (the frequencies are in MHz). In our example, only 9 frequencies have been specified, so two last columns out of 11 are empty. The final column 16

contains 22 parameters that have been calculated for these frequencies in the hour block. The first parameter FREQ indicates the frequency (in MHz) used in calculation.

2.1.5.2

A note about the antenna used in the example

For this general study, a Curtain Array AHR(S) 4/4/1 has been defined but with no design frequency. This means that for every frequency calculated, the design frequency would be set equal to the operating frequency (an idealised antenna). In reality, this situation does not occur. Rarely is one transmitting antenna valid for all frequencies from 6 to 26 MHz. Therefore, you have the ability to define different antennas for different frequency ranges. See Antennas in Setting Up the Parameters.

Graphical circuit prediction (Run > Graph) After you have set all the circuit parameters in the VOACAP main screen, or if you have run a textual circuit prediction, it is time to run the analysis in a graphical mode. Our data example is again from the circuit of Pori (Finland) - Johannesburg (South Africa). Choose Graph from the Run menu (abbreviated later in these web pages as Run > Graph). A new window will open, containing all the available output parameters:

The graphical charts provide a nice overview of the parameters on the frequency/time scale. To view the exact details of the values, click anywhere on the chart, the details appear below the menu bar:

While in a parameter output window, another parameter can be chosen by clicking the Parameters menu. The frequency scale (on the left side) can be changed from the Scale menu. If you wish the window to be pasted into another program, click the to Clipboard menu. To print the window, choose from the Print menu. Some of the most prominent parameters to look at are SNR, REL andSNRxx. Below are those parameters from our circuit. The thick black line that runs through the chart is the median MUF. 17

2.1.6.1

SNR (aka SNR50)

The SNR values (in dB-Hz) that can be maintained 50% of days (15 days) in the month.

2.1.6.2

REL (Circuit Reliability)

The percentage of days in the month when the SNR (SNR50) value will equal to or exceed the REQ.SNR.

18

2.1.6.3

SNRxx (aka SNR90)

The SNR values (in dB-Hz) that can be maintained 90% of days (27 days) in the month.

Area coverage prediction (VOAAREA)

From a point-to-point circuit analysis we can proceed to an area coverage analysis. It sometimes happens that a frequency that is most suitable for a certain point-to-point circuit, is not the best possible for providing good service to a specific area. 19

Let us take our example circuit of Pori (Finland) to Johannesburg (South Africa) at 1 UTC in December 2001. We have had an analysis of this circuit in the article Understanding Above-the-MUF Predictions. It shows that the best frequency would be 11.9 MHz. Now let us see how that frequency would work for the African continent. The following screen reflects the basic settings of VOAAREA - a companion program to VOACAP - needed for running the coverage analysis: We are interested in the circuit reliability in Africa, therefore we choose REL from Parameters. You may choose several parameters at a time. As some locations in our target area are 10,000 km away, we choose theMethod 30, Short/Long Path Model Smoothing. Be sure to select CCIR (Oslo) coefficients (not URSI88). Also, keep the Fprob values as shown above. The following screen shots explain how to set some other input values shown above:

2.1.7.1

Plot Center

2.1.7.2

Groups

20

2.1.7.3

System

2.1.7.4

Running the Maps

Choose Run > Calculate > Save{temp.VOA}/Calculate:

When the calculations are done, choose Run > Plot results. A window will appear, choose File > Open TEMP.VG1:

The following window will appear:

21

To plot the map, just choose Plot to > Window. You can also plot or print the map to the printer. To view the remaining maps, choose File > Open. The file names are of format TEMP.VG? where the question mark is a number between 1 to 7. Furthermore, in this window you can choose several output parameters for viewing if you did not do so in the main screen. Just select them by clicking the Parameters button. If you wish to change the colours or values to be plotted, click theContours button. The following window will appear:

Then click the REL button. The following window will appear:

22

You can change the values and colours here. Note that a value of -999 is used to fill unused lines. Be sure to select a proper colour for that value too! If you change any of the default values, click the Values assigned are:button. The text AUTO scaled will change to defined. Otherwise, your settings will be ignored.

2.1.7.5

Area Coverage Analysis

Using the output parameter of REL, the Circuit Reliability - the percentage of days in the month when the SNR (SNR50) value will equal to or exceed the REQ.SNR. (67 dB-Hz) - the following coverage maps can be produced for the frequencies of 9.7, 11.9, 13.7 and 15.4 MHz at 1 UTC in December 2001. We see that 9.7 MHz can serve a larger portion of Africa than 11.9 MHz. It also provides better service to Europe. The frequencies of 13.7 and 15.4 MHz can provide service to Southern Africa but their overall performance is not adequate. 9.7 MHz

11.9 MHz

13.7 MHz

Legend

15.4 MHz

23

2.2 The calculation engine, VOACAPW An introduction to VOACAPW.EXE The FREQUENCY card in VOACAPX.DAT

An introduction to VOACAPW.EXE VOACAPW.EXE is the program module in the VOACAP program package that is responsible for VOACAP propagation calculations. The graphical VOACAP interface program is mainly responsible for collecting the input and putting it into a format that can be fed into the VOACAPW.EXE program. Further, the graphical VOACAP suite of programs take care of presenting the output that comes as the result of VOACAPW calculations. VOACAPW.EXE can be found in the C:\itshfbc\bin_win\ directory (provided the has accepted the default VOACAP installation options). This program can be invoked in a variety of ways, depending on the type of calculations we wish to run. Below is the summary of the syntax that comes with the program: |------------------------------------------------------------------------------| | The propagation modules VOACAPW.EXE, ICEPACW.EXE, or REC533W.EXE cannot be | | executed individually unless you have created the proper formated data input | | file. You can execute: | | POINTWIN.EXE (point-to-point interface) | | AREAWIN.EXE (area coverage interface) | | SI_WIN.EXE (signal-to-interference interface) | | AREAINV.EXE (inverse area coverage interface) | | HFANTWIN.EXE (antenna interface) | | individually from this directory. | |------------------------------------------------------------------------------| | If you create your own input files in the proper formats, you can use the | | examples below as to how to execute the various propagation modules. | | The examples below are given for VOACAP. To make it run for ICEPAC or | | REC533, just substitute the desired model for VOACAP | |------------------------------------------------------------------------------| | Execute with: | | VOACAPW.EXE [S] directory inputfile outputfile (P-P circuit) | | VOACAPW.EXE [S] directory inputfile outputfile (P-P graph) | | VOACAPW.EXE [S] directory VOACAPD.DAT VOACAPD.OUT (P-P distance) | | VOACAPW.EXE [S] directory VOACAPT.DAT VOACAPT.OUT (P-P time) | | VOACAPW.EXE [S] directory BATCH (P-P batch) | | VOACAPW.EXE [S] directory BATCH deckname.dat (P-P NEW batch) | | VOACAPW.EXE [S] directory BATCH deckname.dat nam.out (P-P NEW batch) | | VOACAPW.EXE [S] directory AREA CALC VOAAREAW.CIR (AREA batch) | | VOACAPW.EXE [S] directory AREA method pathname (AREA single) | | VOACAPW.EXE [S] directory INV CALC VOAAREAW.CIR (AREA INVERSE batch) | | VOACAPW.EXE [S] directory INV method pathname (AREA INVERSE single) | | VOACAPW.EXE [S] directory CIRAF pathname (CIRAF single) | | where: | | [S] = SILENT, then no messages are written to output window | | [S] means either put in SILENT or nothing. | | directory = full pathname to the install directory (e.g. c:\ITSHFBC) | | method = (CALC/SCREEN/PRINT) | | pathname = pathname below directory\AREADATA\ of input data file | | (e.g. DEFAULT\DEFAULT.VOA) | | deckname.dat = a proper formated input "card" deck. | | | | The input and output files ifor point-to-point runs will be in the | | ..\RUN directory. | | | | You will probably need to also include the full pathname to the EXE file. | | Thus, using the default installation directory, the P-P circuit would be: | | |

24

| c:\itshfbc\bin_win\voacapw.exe c:\itshfbc voacapx.dat voacapx.out | | | | Note: Not all options will work for REC533 (e.g. distance, time, & INVERSE) | |------------------------------------------------------------------------------| | The only options you probably want to use are: | | VOACAPW.EXE [S] directory inputfile outputfile (P-P circuit) | | VOACAPW.EXE [S] directory AREA method pathname (AREA single) | | VOACAPW.EXE [S] directory BATCH deckname.dat nam.out (P-P NEW batch) | |------------------------------------------------------------------------------| | | | | |------------------------------------------------------------------------------| | To execute the world map plotting program from a command prompt: | | | | worldwin.exe run_directory data_directory filename noplot | | where: | | run_directory = RUN directory (e.g. C:\ITSHFBC\RUN) | | data_directory= data sub-directory (e.g. AREADATA) | | filename - file in ..\AREADATA\ directory of the | | form subdir\????????.mGn (Grid file) | | where:subdir=sub-directory under ..\AREADATA | | m = V = VOACAP | | m = I = ICEPAC | | m = R = REC533 | | m = C = COVMAP | | n = group number of plot [1-9] | | = 'voaareax.da?' means read for filename | | = 'areapltx.dat' means read for filename | | noplot = ' ' = do worldwin plot with wait | | = 'n' = do worldwin plot with no wait | | = 'b' = do worldwin plot with no wait,force B/W | | = 'x' = do not do worldwin | | = 'p' = do worldwin to Printer only | | = 's' = do worldwin to Screen only | | = 'm' = map only, no contours | | Will create ????????.mxn (contour file) | | where: x = index [1-9] of parameters contoured | | | | Thus, it can be exeuted with: | | c:\itshfbc\bin_win\worldwin c:\itshfbc\run areadata default\default.ig1 | | | |------------------------------------------------------------------------------| |------------------------------------------------------------------------------|

2.2.1.1

Running Point-to-point (P-P) circuit calculations

Let us start exploring VOACAPW.EXE by using it for point-to-point circuit calculations. As we can see in the summary above, the input data file used for calculations is VOACAPX.DAT and the results will be written into VOACAPX.OUT. VOACAPX.DAT and VOACAPX.OUT are both located in the C:\itshfbc\run directory. To run the calculations in silent mode, enter the following command in the C:\itshfbc\bin_win directory: voacapw silent C:\itshfbc voacapx.dat voacapx.out

To run the calculations in normal mode (when the calculations appear in the output window), use the following command: voacapw C:\itshfbc voacapx.dat voacapx.out

2.2.1.2

Setting the VOACAPX.DAT input file

As we are running VOACAPW.EXE from the command prompt, we will need to make sure that the input file is in the format accepted by the program. Take a look at the following the example VOACAPX.DAT file 25

generated by the graphical VOACAP program after you choose the Circuit command from the Run menu for the circuit of Pori (Finland) to Johannesburg (South Africa): COMMENT Any VOACAP default cards may be placed in the file: VOACAP.DEF LINEMAX 55 number of lines-per-page COEFFS CCIR TIME 1 24 1 1 MONTH 2002 7.00 SUNSPOT 96. LABEL PORI JOHANNESBURG CIRCUIT 61.48N 21.78E 26.25S 28.00E S 0 SYSTEM 1. 155. 3.00 90. 67.0 3.00 0.10 FPROB 1.00 1.00 1.00 0.00 ANTENNA 1 1 2 30 0.000[hfcc\HFBC_218.P15 ]175.0 350.0000 ANTENNA 2 2 2 30 0.000[default\SWWHIP.VOA ] 0.0 0.0000 FREQUENCY 6.07 7.20 9.7011.8513.7015.3517.7321.6525.89 0.00 0.00 METHOD 30 0 EXECUTE QUIT

2.2.1.3

Six advantages of manual tuning of VOACAPX.DAT

1. You can run predictions for the entire year, ie. 12 months. If you are using the graphical VOACAP interface program, you can enter only 10 month/SSN value pairs. These two lines practically go hand in hand: MONTH SUNSPOT

2002 7.00 96.

The definition lines for the entire year could be as follows (the year 2002 with the predicted smoothed sunspot numbers): MONTH SUNSPOT

2002 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.0010.0011.0012.00 110. 109. 106. 103. 101. 98. 96. 93. 90. 87. 85. 81.

2. You can define a total of up to 20 antennas: ten transmit and ten receive antennas. If you were using the graphical VOACAP program, you could define a total of five antennas, four transmit antennas and one receive antenna. In our example above, we had one transmit antenna and one receive antenna: ANTENNA ANTENNA

1 2

1 2

2 2

30 30

0.000[hfcc\HFBC_218.P15 0.000[default\SWWHIP.VOA

]175.0 ] 0.0

350.0000 0.0000

Let us assume we have an amateur radio station with a good selection of antennas at our disposal. Our definition of antennas for VOACAPW.EXE could be as follows: ANTENNA ANTENNA ANTENNA ANTENNA ANTENNA ANTENNA ANTENNA ANTENNA ANTENNA ANTENNA

1 1 1 1 1 1 2 2 2 2 (1)

1 2 3 4 5 6 7 8 9 10

2 11 15 22 24 27 2 11 15 22

11 15 22 24 27 30 11 15 22 30

(2)

(3)

(4)

12.000[default\CCIR.000 0.000[omat\3elhw.ANT 0.000[omat\3elone.ANT 0.000[omat\3eloq.ANT 0.000[omat\3elo3q.ANT 0.000[omat\3eltwo.ANT 6.000[default\CCIR.000 0.000[omat\3elhw.ANT 0.000[omat\3elone.ANT 0.000[omat\3eloq.ANT (5)

(6)

] 0.0 ]175.0 ]175.0 ]175.0 ]175.0 ]175.0 ] 0.0 ]357.0 ]357.0 ]357.0 (7)

0.5000 0.1000 1.0000 1.0000 1.5000 0.1000 6.0000

(8)

The explanations of the columns are as follows: (1) The type of the antenna: 1 = transmit, 2 = receive. (2) The order number of the antenna from 1 to 20. If you define more than 20 antennas, VOACAPW.EXE will crash.

26

(3) The minimum frequency for the antenna (in MHz). (4) The maximum frequency for the antenna (in MHz). (5) The design frequency. However, for isotropic antennas, it is the gain (as in the case of the CCIR.000 antenna). The design frequency of zero in our example means that the design frequency = operating frequency. (6) The path to the antenna definition file under the C:\itshfbc\antennas directory. (7) The main beam of the antenna. (8) For transmit antennas: the power (in kW). NOTE! You can define a different power level for each of the transmit antennas! For receive antennas: the gain (in dBi, applicable only to isotropic antennas).

3. You can run several Methods in one go. Otherwise, you would run only one Method per one file. In our example circuit, we defined Method 30 (Short/Long Path Smoothing): METHOD

30 (1)

0 (2)

Explanation: (1) The Method we wish to use for our circuit. (2) The start page number in the result (output) file.

If we wanted to run both Method 30 (Short/Long Path Smoothing) and Method 9 (HPF-MUF-FOT Graph) for our circuit, we would write the following lines: METHOD EXECUTE METHOD EXECUTE

30

0

9

0

Now VOACAPW.EXE first executes Method 30 for the input data entered above, and then Method 9 for the same input data. If you take a look at the result file (VOACAPX.OUT), you will see that the graphs for our newly-specified 12 months follows the Method 30 output data. If we implement all our modifications so far, the input file looks like this: COMMENT Any VOACAP default cards may be placed in the file: VOACAP.DEF LINEMAX 55 number of lines-per-page COEFFS CCIR TIME 1 24 1 1 MONTH 2002 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.0010.0011.0012.00 SUNSPOT 110. 109. 106. 103. 101. 98. 96. 93. 90. 87. 85. 81. LABEL PORI JOHANNESBURG CIRCUIT 61.48N 21.78E 26.25S 28.00E S 0 SYSTEM 1. 155. 3.00 90. 67.0 3.00 0.10 FPROB 1.00 1.00 1.00 0.00 ANTENNA 1 1 2 11 12.000[default\CCIR.000 ] 0.0 0.1000 ANTENNA 1 2 11 15 0.000[omat\3elhw.ANT ]175.0 0.1000 ANTENNA 1 3 15 22 0.000[omat\3elone.ANT ]175.0 0.1000 ANTENNA 1 4 22 24 0.000[omat\3eloq.ANT ]175.0 0.1000 ANTENNA 1 5 24 27 0.000[omat\3elo3q.ANT ]175.0 0.1000 ANTENNA 1 6 27 30 0.000[omat\3eltwo.ANT ]175.0 0.1000 ANTENNA 2 7 2 11 6.000[default\CCIR.000 ] 0.0 6.0000 ANTENNA 2 8 11 15 0.000[omat\3elhw.ANT ]357.0 ANTENNA 2 9 15 22 0.000[omat\3elone.ANT ]357.0 ANTENNA 2 10 22 30 0.000[omat\3eloq.ANT ]357.0 FREQUENCY 6.07 7.20 9.7011.8513.7015.3517.7321.6525.89 0.00 0.00 METHOD 30 0 EXECUTE METHOD 9 0 EXECUTE

27

QUIT

Please note that running this file produces a 300-page result file!

4. Defining more than 11 FREQUENCIES for calculations. Below we run 18 frequencies: COMMENT Any VOACAP default cards may be placed in the file: VOACAP.DEF LINEMAX 55 number of lines-per-page COEFFS CCIR TIME 1 24 1 1 MONTH 2002 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.0010.0011.0012.00 SUNSPOT 110. 109. 106. 103. 101. 98. 96. 93. 90. 87. 85. 81. LABEL PORI JOHANNESBURG CIRCUIT 61.48N 21.78E 26.25S 28.00E S 0 SYSTEM 1. 155. 3.00 90. 67.0 3.00 0.10 FPROB 1.00 1.00 1.00 0.00 ANTENNA 1 1 2 11 12.000[default\CCIR.000 ] 0.0 0.1000 ANTENNA 1 2 11 15 0.000[omat\3elhw.ANT ]175.0 0.1000 ANTENNA 1 3 15 22 0.000[omat\3elone.ANT ]175.0 0.1000 ANTENNA 1 4 22 24 0.000[omat\3eloq.ANT ]175.0 0.1000 ANTENNA 1 5 24 27 0.000[omat\3elo3q.ANT ]175.0 0.1000 ANTENNA 1 6 27 30 0.000[omat\3eltwo.ANT ]175.0 0.1000 ANTENNA 2 7 2 11 6.000[default\CCIR.000 ] 0.0 6.0000 ANTENNA 2 8 11 15 0.000[omat\3elhw.ANT ]357.0 ANTENNA 2 9 15 22 0.000[omat\3elone.ANT ]357.0 ANTENNA 2 10 22 30 0.000[omat\3eloq.ANT ]357.0 FREQUENCY 6.07 7.20 9.7011.8513.7015.3517.7321.6525.89 0.00 0.00 METHOD 30 0 EXECUTE FREQUENCY 2.00 3.70 7.0510.0714.1818.1021.2324.9528.30 0.00 0.00 EXECUTE QUIT

This run produces 576 pages or 23,650 output lines!

5. Defining an alternative set of SYSTEM parameters for the given circuit COMMENT Any VOACAP default cards may be placed in the file: VOACAP.DEF LINEMAX 55 number of lines-per-page COEFFS CCIR TIME 1 24 1 1 MONTH 2002 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.0010.0011.0012.00 SUNSPOT 110. 109. 106. 103. 101. 98. 96. 93. 90. 87. 85. 81. LABEL PORI JOHANNESBURG CIRCUIT 61.48N 21.78E 26.25S 28.00E S 0 SYSTEM 1. 155. 3.00 90. 67.0 3.00 0.10 FPROB 1.00 1.00 1.00 0.00 ANTENNA 1 1 2 11 12.000[default\CCIR.000 ] 0.0 0.1000 ANTENNA 1 2 11 15 0.000[omat\3elhw.ANT ]175.0 0.1000 ANTENNA 1 3 15 22 0.000[omat\3elone.ANT ]175.0 0.1000 ANTENNA 1 4 22 24 0.000[omat\3eloq.ANT ]175.0 0.1000 ANTENNA 1 5 24 27 0.000[omat\3elo3q.ANT ]175.0 0.1000 ANTENNA 1 6 27 30 0.000[omat\3eltwo.ANT ]175.0 0.1000 ANTENNA 2 7 2 11 6.000[default\CCIR.000 ] 0.0 6.0000 ANTENNA 2 8 11 15 0.000[omat\3elhw.ANT ]357.0 ANTENNA 2 9 15 22 0.000[omat\3elone.ANT ]357.0 ANTENNA 2 10 22 30 0.000[omat\3eloq.ANT ]357.0 FREQUENCY 6.07 7.20 9.7011.8513.7015.3517.7321.6525.89 0.00 0.00 METHOD 30 0 EXECUTE SYSTEM 1. 155. 0.10 90. 27.0 3.00 0.10 EXECUTE QUIT

28

6. Running a set of different CIRCUITS while keeping other parameters fixed COMMENT LINEMAX COEFFS TIME MONTH SUNSPOT LABEL CIRCUIT SYSTEM FPROB ANTENNA ANTENNA FREQUENCY METHOD EXECUTE LABEL CIRCUIT EXECUTE LABEL CIRCUIT EXECUTE QUIT

Any VOACAP default cards may be placed in the file: VOACAP.DEF 55 number of lines-per-page CCIR 1 24 1 1 2002 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.0010.0011.0012.00 110. 109. 106. 103. 101. 98. 96. 93. 90. 87. 85. 81. PORI JOHANNESBURG 61.48N 21.78E 26.25S 28.00E S 0 1. 155. 3.00 90. 67.0 3.00 0.10 1.00 1.00 1.00 0.00 1 1 2 30 0.000[default\CONST17.VOA ] 0.0 350.0000 2 2 2 30 0.000[default\SWWHIP.VOA ] 0.0 0.0000 6.07 7.20 9.7011.8513.7015.3517.7321.6525.89 0.00 0.00 30 0 PORI 61.48N

21.78E

WELLINGTON 41.28S 174.78E

S

0

PORI 61.48N

21.78E

NEW YORK 40.43N

S

0

74.00W

Please note that while running different circuits in one go, you must use a fixed antenna configuration for all the circuits! In our example we have chosen an omnidirectional 17-dBi antenna for testing purposes.

The FREQUENCY card in VOACAPX.DAT The VOACAPW.EXE is the calculation engine in the VOACAP that accepts the VOACAPX.DAT as input. This data input file is composed of a number of "control cards", or labeled lines. There are a few things you can do with the FREQUENCY card (line) that are not available when using the VOACAP GUI for creating the data input file. Below is the normal structure of VOACAPX.DAT (as created by the VOACAP GUI) when I want to know about the path from Vaasa (Finland) to New York (USA) on 7.05, 10.12 and 14.05 MHz: COMMENT Any VOACAP default cards may be placed in the file: VOACAP.DEF LINEMAX 55 number of lines-per-page COEFFS CCIR TIME 1 24 1 1 MONTH 2003 7.00 SUNSPOT 63. LABEL VAASA NEW YORK CIRCUIT 63.10N 21.60E 40.72N 74.00W S 0 SYSTEM 1. 155. 3.00 90. 24.0 3.00 0.10 FPROB 1.00 1.00 1.00 0.00 ANTENNA 1 1 2 30 0.000[default\CCIR.000 ] 0.0 0.1000 ANTENNA 2 2 2 30 0.000[default\SWWHIP.VOA ] 0.0 0.0000 FREQUENCY 7.0510.1214.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 METHOD 30 0 EXECUTE QUIT

First of all, it is important to note that the placement of decimal points for frequencies on the FREQUENCY line is crucial since they are in fixed positions. You can mess the frequencies up big time if you are not careful. This is probably one of the reasons that there is an interface program that takes care of things like this. Typically, the FREQUENCY line accepts up to 11 defined frequencies. However, there are other ways of using the FREQUENCY line. 29

2.2.2.1

Calculating from 2 to 30 MHz

If you want to calculate the prediction for the whole HF range on the given path from 2.0 MHz to 30.0 MHz in 1.0 MHz steps, you write as follows: FREQUENCY -1

The start of the result pages would be as follows: CCIR Coefficients

~METHOD 30

VOACAP 03.0724W

PAGE

1

Jul 2003 SSN = 63. Minimum Angle= 3.000 degrees VAASA NEW YORK AZIMUTHS N. MI. KM 63.10 N 21.60 E - 40.72 N 74.00 W 295.58 32.58 3406.9 6309.2 XMTR 2-30 + 0.0 dBi[default\CCIR.000 ] Az= 0.0 OFFaz=295.6 0.100kW RCVR 2-30 2-D Table [default\SWWHIP.VOA ] Az= 0.0 OFFaz= 32.6 3 MHz NOISE = -155.0 dBW REQ. REL = 90% REQ. SNR = 24.0 dB MULTIPATH POWER TOLERANCE = 3.0 dB MULTIPATH DELAY TOLERANCE = 0.100 ms 1.0 14.3 2F2 7.7 22.5 434 0.50 171 -18 -151 -171 20 30 0.42 0.00 0.20 25.0 25.0 25.9 25.4 0.0 -2.0 -6

2.0 4 E 3.0 21.3 92 1.00 203 -61 -181 -144 -37 81 0.00 0.00 0.00 16.4 8.3 19.8 13.3 0.0 -7.5 -57

3.0 4F2 21.5 23.9 380 1.00 183 -36 -154 -149 -5 48 0.00 0.00 0.04 16.4 8.3 19.2 12.6 0.0 0.0 -24

4.0 3F2 13.8 22.8 362 1.00 168 -22 -141 -152 11 32 0.08 0.02 0.11 16.4 8.3 18.8 12.0 0.0 -0.5 -8

5.0 3F2 11.0 22.4 304 1.00 158 -14 -135 -154 19 24 0.27 0.12 0.17 16.4 8.3 18.4 11.6 0.0 -1.1 0

6.0 3F2 10.3 22.3 289 1.00 156 -7 -133 -156 23 19 0.46 0.24 0.21 16.4 8.3 18.2 11.1 0.0 -1.2 5

7.0 3F2 10.0 22.2 284 1.00 155 -4 -132 -158 26 17 0.55 0.32 0.24 16.8 8.3 18.3 10.8 0.0 -1.3 7

8.0 3F2 10.1 22.2 286 0.99 154 -6 -132 -159 27 17 0.58 0.42 0.27 18.5 8.8 19.7 10.9 0.0 -1.3 7

9.0 3F2 10.4 22.3 292 0.94 154 -5 -133 -161 28 17 0.60 0.00 0.28 20.1 9.1 21.2 11.0 0.0 -1.2 7

10.0 2F2 3.1 21.8 291 0.99 157 -1 -132 -163 30 16 0.64 0.59 0.27 21.0 8.8 22.0 10.5 0.0 -7.4 8

0.0 -

0.0 -

FREQ MODE TANGLE DELAY V HITE MUFday LOSS DBU S DBW N DBW SNR RPWRG REL MPROB S PRB SIG LW SIG UP SNR LW SNR UP TGAIN RGAIN SNRxx

The MUF is 14.3 MHz at 01 UTC, followed by frequencies starting from 2.0 MHz. The output file consists of many pages...

2.2.2.2

Calculating the FOT

If you want to calculate the frequencies of your interest as well as the FOT ("the frequency of optimum traffic", or frequency where MUFday = 0.90), you write as follows: FREQUENCY

0.00 7.0510.1214.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00

As you can see, the first frequency on the line is zero. What that will do is the output for frequencies: MUF FOT f1 f2 f3 ...

The start of the result pages would be as follows: CCIR Coefficients

~METHOD 30

Jul 2003 SSN = 63. VAASA NEW YORK 63.10 N 21.60 E - 40.72 N 74.00 W

VOACAP 03.0724W

PAGE

1

Minimum Angle= 3.000 degrees AZIMUTHS N. MI. KM 295.58 32.58 3406.9 6309.2

30

XMTR 2-30 + 0.0 dBi[default\CCIR.000 ] Az= 0.0 OFFaz=295.6 RCVR 2-30 2-D Table [default\SWWHIP.VOA ] Az= 0.0 OFFaz= 32.6 3 MHz NOISE = -155.0 dBW REQ. REL = 90% REQ. SNR = 24.0 dB MULTIPATH POWER TOLERANCE = 3.0 dB MULTIPATH DELAY TOLERANCE = 1.0 14.3 2F2 7.7 22.5 434 0.50 171 -18 -151 -171 20 30 0.42 0.00 0.20 25.0 25.0 25.9 25.4 0.0 -2.0 -6

11.9 2F2 3.7 21.9 310 0.90 156 -1 -136 -166 30 19 0.62 0.00 0.29 24.1 9.0 24.9 10.3 0.0 -6.0 5

7.1 3F2 10.0 22.2 284 1.00 155 -4 -132 -158 26 16 0.55 0.33 0.24 16.8 8.3 18.3 10.8 0.0 -1.3 8

10.1 2F2 3.1 21.8 291 0.99 157 -1 -132 -163 30 16 0.65 0.59 0.28 21.1 8.9 22.0 10.6 0.0 -7.4 8

14.1 2F2 6.0 22.2 379 0.56 164 -10 -143 -170 27 23 0.56 0.00 0.26 25.0 20.0 25.9 20.4 0.0 -3.2 1

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

0.100kW 0.100 ms

FREQ MODE TANGLE DELAY V HITE MUFday LOSS DBU S DBW N DBW SNR RPWRG REL MPROB S PRB SIG LW SIG UP SNR LW SNR UP TGAIN RGAIN SNRxx

The MUF is 14.3 MHz, the FOT is 11.9 MHz and the rest of the frequencies are my 7.05, 10.12 and 14.05 MHz.

2.2.2.3

Calculating from 2 MHz to the HPF

Lastly, there is an option to calculate from 2.0 MHz to the HPF. The HPF is "the highest possible frequency", or the frequency where the value of MUFday reaches 0.10. You would put: FREQUENCY 0

or FREQUENCY 0 -1

The start of the result pages would be as follows: CCIR Coefficients

~METHOD 30

VOACAP 03.0724W

PAGE

1

Jul 2003 SSN = 63. Minimum Angle= 3.000 degrees VAASA NEW YORK AZIMUTHS N. MI. KM 63.10 N 21.60 E - 40.72 N 74.00 W 295.58 32.58 3406.9 6309.2 XMTR 2-30 + 0.0 dBi[default\CCIR.000 ] Az= 0.0 OFFaz=295.6 0.100kW RCVR 2-30 2-D Table [default\SWWHIP.VOA ] Az= 0.0 OFFaz= 32.6 3 MHz NOISE = -155.0 dBW REQ. REL = 90% REQ. SNR = 24.0 dB MULTIPATH POWER TOLERANCE = 3.0 dB MULTIPATH DELAY TOLERANCE = 0.100 ms 1.0 14.3 2.0 3.7 5.5 5.5 7.2 8.9 10.7 12.4 14.1 15.9 17.6 FREQ 2F2 4 E 3F2 3F2 3F2 3F2 3F2 2F2 2F2 2F2 2F2 2F2 MODE 7.7 3.0 15.2 10.6 10.5 10.0 10.4 3.2 4.0 6.5 7.7 7.7 TANGLE 22.5 21.3 23.1 22.3 22.3 22.2 22.3 21.8 21.9 22.3 22.5 22.5 DELAY 434 92 394 295 294 284 292 296 319 396 434 434 V HITE 0.50 1.00 1.00 1.00 1.00 1.00 0.95 0.97 0.84 0.54 0.27 0.10 MUFday 171 203 173 157 157 155 154 157 156 165 187 215 LOSS -18 -61 -25 -11 -10 -7 -5 -1 -2 -12 -34 -61 DBU

31

-151 -171 20 30 0.42 0.00 0.20 25.0 25.0 25.9 25.4 0.0 -2.0 -6

-181 -144 -37 81 0.00 0.00 0.00 16.4 8.3 19.8 13.3 0.0 -7.5 -57

-144 -151 7 36 0.04 0.00 0.09 16.4 8.3 18.9 12.2 0.0 -0.4 -12

-134 -155 21 22 0.35 0.16 0.19 16.4 8.3 18.3 11.4 0.0 -1.2 2

-134 -155 21 21 0.37 0.17 0.20 16.4 8.3 18.3 11.3 0.0 -1.2 3

-132 -158 26 17 0.54 0.34 0.25 17.6 8.4 19.0 10.8 0.0 -1.3 7

-133 -161 28 17 0.60 0.00 0.28 20.0 9.1 21.0 10.9 0.0 -1.2 7

-133 -164 31 16 0.65 0.58 0.28 21.5 9.7 22.4 11.2 0.0 -7.1 8

-136 -167 31 19 0.63 0.00 0.29 25.0 9.7 25.8 10.9 0.0 -5.4 5

-144 -170 26 24 0.54 0.00 0.24 25.0 21.8 25.9 22.2 0.0 -2.8 0

-167 -174 7 44 0.19 0.00 0.11 25.0 25.0 26.1 25.3 0.0 -2.0 -20

-195 -177 -18 68 0.02 0.00 0.03 25.0 25.0 26.3 25.3 0.0 -2.0 -44

S DBW N DBW SNR RPWRG REL MPROB S PRB SIG LW SIG UP SNR LW SNR UP TGAIN RGAIN SNRxx

Here, the MUF is again 14.3 MHz, the first frequency to the right of the MUF is 2.0 MHz and the last is 17.6 MHz which is the HPF (MUFday = 0.10) at 01 UTC. The HPF is obviously different from hour to hour. The remaining nine frequencies are "computed on a non-linear scale based on the E-MUF and F-MUF values". This comes from the original IONCAP and can be elaborated by those more knowledgeable in the IONCAP theory. :-) Thanks to Greg Hand for explaining the FREQUENCY parameters.

2.3 Graphs & Colours VOACAP & VOAAREA contours VOACAP & VOAAREA plot colors Y-axis scaling for VOACAP Time & Distance graphs

VOACAP & VOAAREA contours There are three files, located in the default installation atC:\itshfbc\database\, where the contour values are defined for output parameters, to be used in VOACAP graphs & VOAAREA coverage maps: VOACAP VOAPLT

GPH GPH

2.3.1.1

VOACAP Point-to-Point parameter auto scaling info VOACAP auto scaling data used by AREAPLTW.EXE

Syntax

xfact, icode, num, [ con(num) ]

Where: xfact = multiplying factor Usually either 1. or 100. (100 for percents) icode = calculating code 0 1 2 3 num

= = = =

-defined values given in CON (max of 6 allowed **) MAX down in CON(1) increments, Min allowed CON(2) MIN to MAX in 6 program-defined steps MIN up in CON(1) increments, Max allowed CON(2)

= number of numeric arguments to follow.

con(num) = numeric arguments, up to num If num = 2, then two arguments have to follow. They become CON(1) and CON(2). When num = 0, there are no numeric arguments (icode = 2). The max value of num = 6 can only be used in the case of icode = 0.

32

** in reality, VOACAPW.EXE accepts 10 -defined values. These need to be defined in the data input card.

2.3.1.2

Contour colors

The default values will be read from C:\itshfbc\database\colors.gph (for graphs) and C:\itshfbc\database\colors.con (for coverage maps). Seehttp://www.uwasa.fi/~jpe/voacap/colors.html

2.3.1.3

Examples

1. DEFINED CONTOUR VALUES (ICODE = 0) MUFday= % of days/month sky-wave propagation expected at MUF mode MUF days expected [%] 100. 0 6 1. 10. 50. 90. 99. 110.

Explanations:  

Multiply values in datafile by 100. Use 6 values given.

2. PROGRAM DEFINED MAX TO DEFINED MIN + INCREMENT (ICODE = 1) DBU

= Median field strength at receive location (dBu) Field Strength Median [dBu] 1. 1 2 5. 0.

Explanations:   

Find MAX in datafile (e.g. say it was 69) Round up to the next multiple of CON(1) (70 in this case). Contours start at 70 (but you will not see this one) and go down in steps of 5 [= CON(1)] for 6 contours. The lower limit will be 0 [= CON(2)]. Thus, if max was 14, contours would be >10, 5, <0.

3. PROGRAM DEFINED MAX, MIN AND INCREMENT (ICODE = 2) TANGLE= Radiation angle (degrees) Radiation Angle Transmit 1. 2 0

[degrees]

Explanations: 

Find MIN and MAX in datafile (e.g. 4.6, 32.3) The steps are based on a complicated algorithm, but it essentially finds 6 contours within the min and max. In this case it would find <6,12,18,24,30,>30.

4. PROGRAM DEFINED MIN TO DEFINED MAX AND INCREMENT (ICODE = 3) RPWRG = Required power & antenna gain to achieve reliab (dB) Required Power & Antenna Gain [dB] 1. 3 2 10. 200.

Explanations:  

Find MIN in datafile Round down to the next multiple of CON(1) 33



Contours start at this value and go up in steps of 10 [= CON(1)] for 6 contours. The upper limit is 200 [= CON(2)]. icode=3 is opposite of icode=1, and is used for values that are really negative, but are calculated as positive values (such as LOSS & RPWRG).

VOACAP & VOAAREA plot colors There are two definition files, located in the default installation atC:\itshfbc\database\, that define the plot colors for VOACAP graphs and VOAAREA coverage maps as follows: COLORS COLORS

GPH CON

2.3.2.1

Colors for auto contour shading for Point-to-Point plots Colors for auto contour shading for Area Coverage plots

Point-to-Point Plots

Colors.gph - original 8 7 1 4 dark grey grey

1 2 3 15 6 56 58 59 red gren yell whit

Color indexes Black/White shade codes

This controls the colors used for Point-to-Point graph shading. On the first line, place 6 colors used for auto shading. On the 2nd line, place the shading codes to be used for black/white shading. The right-most value corresponds to the highest value shaded. Below is a list of the value colors that may be used. Using an invalid color value will cause the default values to be used. 0=Black 1=Red 2=Green 3=Yellow

4=Blue 5=Magenta 6=Cyan 7=Grey

8=Dark grey 9=Orange 10=Lite green 11=Brown

12=Lite blue 13=Pink 14=Pale blue 15=White

For point-to-point graphs we could use the following color scale (originally suggested by Dan AC6LA at http://www.qsl.net/ac6la/mapcontrol.html) [from highest to lowest value]: Red, Orange, Yellow, Light Green, Pale Blue, Grey.

For the color abbreviations, see file COLORS.WIN in the same DATABASE directory. Subsequently, you would change the first line of COLORS.GPH to:

7

14

10

3

9

1

Color indexes

Now these 6 colors are always automatically selected for graphs. 34

We will now change the Area Coverage colors accordingly:

2.3.2.2

Area Coverage Plots

Colors.con - original 15 7 6 14 whit grey cyan pale blue

2 3 9 grn yell orng

This controls the colors used for auto contour shading. On the first line, place 7 colors used for auto shading. The right-most value corresponds to the highest value shaded. Below is a list of the value colors that may be used. Using an invalid color value will cause the default values to be used. 0=Black 1=Red 2=Green 3=Yellow

4=Blue 5=Magenta 6=Cyan 7=Grey

8=Dark grey 9=Orange 10=Lite green 11=Brown

12=Lite blue 13=Pink 14=Pale blue 15=White

Let us use the color scale suggested by Dan AC6LA (from highest to lowest value): Red, Orange, Yellow, Light Green, Pale Blue, Magenta, Grey.

Subsequently, you would change the two first lines of COLORS.CON to: 7 5 14 10 3 9 grey magn llbl lgrn yell orng

1 red

Now these 7 colors are always automatically selected for Area Coverage plots, so no laborous manual color definitions while plotting are needed from our part. And while using the VOAAREA program, my settings under the LAYERS button are:      

Grid = Grey Countries = Blue (or Black) Zones = Ignore Cities = Ignore MainBeam = Red Contours = Shading, no contours

Y-axis scaling for VOACAP Time & Distance graphs The VOACAP Time and Distance Plots (Run > Time and Run > Distance) are very informative graphs that let you compare the output parameter values for -specified frequencies. The Time Plot lets you view the output parameters on a 24-hour scale, e.g. if you want to see which of the specified frequencies is best at the given time of day.

35

The Distance Plot calculates the variation of output parameter values with regards to distance at the specified hour. By default, most of the output parameter values are automatically scaled. There are, however, some parameters which could benefit from a fixed Y-scale. The Y-axis scaling info is found inC:\itshfbc\database\voadist.gph. VOADIST

GPH

2.3.3.1

VOACAP Point-to-Point parameter Y-scale info

Syntax

The variable names are: xfact,icode,zmin,zmax,zlab,zinc xfact = The multiplier factor, usually 1 or 100 [for percentages] icode = 0 = zmin & zmax are fixed. = 1 = zmin & zmax are calculated from data. zmin = minimum Y value on axis zmax = maximun Y value on axis zlab = number label at every ZLAB increment zinc = tick mark at every ZINC increment

Example 1 SDBW

= Median signal power at receiver (dBW) Signal Power at Receiver (dBW) 1. 0 -160. -50. 10. 2.

Explanation:    

Set the minimum value to -160 (corresponds to [median] S0 on the S-meter) Set the maximum value to -50 (corresponds to [median] > S9 + 40 dB) Set the number label at every 10th increment Set the Y-axis tick mark at every 2nd increment

Example 2 SNR

= Median signal-to-noise ratio (dB) Signal-to-Noise (Median) (dB) 1. 0 0. 100. 10. 2.

Explanation:    

Set the minimum value to 0. This is, in fact, too low. A minimum value of 20 would do. Set the maximum value to 100. For big BC stations, this can be too low a max value... Set the number label at every 10th increment Set the Y-axis tick mark at every 2nd increment

Example 3 SNRxx = Signal-to-Noise ratio (dB) at Req. Rel. Signal-to-Noise at Req. Rel. (dB) 1. 0 0. 100. 10. 2

Explanation:    

Set the minimum value to 0. This is, in fact, too low. A minimum value of 20 would do. Set the maximum value to 100. Now, this can be too high a value. However, now at least, the SNR and SNRxx scales are the same. Set the number label at every 10th increment Set the Y-axis tick mark at every 2nd increment 36

3 VOACAP - Understanding the Prediction 3.1 General Ten Common Mistakes in Using VOACAP This story is supposed to be taken in a light note although these are the potential risk areas that can turn your prediction upside down :-)Some of the issues covered here seem to be rather commonplace according to my searches using Google... however, it's another story how serious these all really are: some are very serious and some are not. You may have compiled altogether different selections, and therefore, it would be nice to hear about them :-) Enjoy! 1. The use of the URSI coefficients. - This seems to be a more common mistake than you might expect, and it may even happen without your knowledge! Use the CCIR Coefficients. See also Mistake 5. 2. The choice of a wrong Smoothed Sunspot Number for the month. - The resource that maintains the (predicted) SSN figures based on the Lincoln-McNish smoothing function to be used with VOACAP is located presently at the address below. These are the sunspot numbers used in the database reduction for the maps used in IONCAP and now VOACAP. ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SUNSPOT_NUMBERS/sunspot.predict I don't know where the hfradio.org site, for example, takes its numbers from but they are not from this resource. WARNING: Absolutely do not use a daily Sunspot Number here! 3. The use of an unsuitable Required SNR (REQ.SNR) value for the transmission mode. - This, too, is difficult for a number of people - and of course it varies case by case, depending on the grade of service you wish to achieve. However, you can immediately see if there is something wrong with these values, say 73 for CW ;-) Perhaps a common start value for CW is 24/27, 40 for SSB and 67 for BC. And, yes, the values are in dB*Hz. 4. The use of a wrong transmitting power. - The transmitting power to use is the power at the antenna feedpoint, not at the back of your transmitter :-) Therefore, a rule of thumb could be that you use 70% of the transmitter output power as the power at the feedpoint. I gladly it I break this rule on a regular basis ;-) And you really have to pay attention and enter all values in kW, so 1 watt is 0.001 kW. 5. Entering a Day in the Month/SSN Groups window. - This is where you can make an unconscious mistake (see Mistake 1). In Groups, there should only be the number of the month (e.g. "7.00" or "8.00" and so on) and its corresponding SSN. If you enter a day within the month (say "7.29" where 7 is July and 29 is the day), you will ruin your prediction :-) Using the day automatically forces VOACAP to use the URSI Coefficients for calculations. And it does so without any warnings! 6. Setting a wrong Required Reliability (REQ.REL.) value. - This can be somewhat a matter of taste but I would suggest always to use the value of 90%. Of course, if you know what you are doing, then it's OK :) I can figure out at least one advantage with 90%: you can determine the best operating frequency just by looking for the highest SNRxx value, right? 7. Setting too much/little man-made noise. - This is again difficult. The default value of 145 is a good starting point. Here in Finland, if you go to the countryside, you can regularly enter 164 (remote) since the only noise 37

comes from within your receiver - or from your head ;-) In the cities, it is a different story. In the suburbs, I guess 155 is, at least in this country, suitable. 8. Setting far too optimistic a Minimum Angle. - As discussed inanother article, the default value of 0.1 degrees is usually too good to be true in the context of amateur radio. There are rare exceptions, though. Use 3.0 degrees and it will be good. This is especially true if you use isotropic antennas; 0.1 degrees is absolutely out of question! 9. Selecting a wrong antenna. - You have to investigate your antenna and its characteristics with the HFANT software, no exceptions :-) You cannot be always certain that the azimuth and elevation patterns are as you expect. Otherwise, you may choose an antenna which has nothing to do with the case in hand - so the prediction will be in danger. 10. The use of a wrong Method. - Most of us needs only a few Methods. I use regularly Method 30, sometimes Method 25 and Method 21. If I calculate FOT-MUF-HPF curves, then I use Method 9. A good starting point is Method 30, really. For the other Methods, you will need to know what you are doing since only part of the available Methods were tested and verified during the development of VOACAP. For instance, Method 9 was not among them but Methods 30, 25 and 21 were.

Field Strength vs. Signal-to-Noise I am a beginner in VOACAP. Why is the Signal-to-Noise ratio more important than the Field Strength? There seems to be two schools of thought here. George Lane: Think of an HF circuit as a telephone link. On one end a modulated signal is introduced which contains information (voice, data, etc). The modulated signal is amplified by the transmitter and raised to RF. The RF is then introduced to the transmit antenna which must efficiently accept this power and launch it into a window in space. This window is defined by the azimuthal spread of the great circle route (usually plus or minus about 2 degrees for point-to-point circuits or by the width of the broadcast target area). The vertical height of the window is determined by the ionospheric modes which will that frequency to the intended target area. The trip through the ionosphere attenuates the signal power until it is delivered to the receive location as a power flux density (or as some people say, a field strength). At this point we must consider the receive antenna pattern. This pattern should be such that it only accepts waves arriving within the ionospheric window defined by azimuth angle and arrival angles of the ionospheric modes (hops). However, the receive antenna accepts some energy at all angles. Any receive antenna over perfect earth will have an average or integrated gain of 3 dB (it receives both the direct wave and also the ground reflected wave - hence twice the power or 3 dB). RF noise power is arriving at the receive site from all directions (atmospheric, man-made and galactic). This noise power is picked up by the receive antenna with 3 dB of gain in the lossless case. The receiver accepts both the signal and all of the noise power within the band filters of the receiver. The ability of the person or device to extract information from the receive signal is dependent on the signal power being sufficiently above the noise floor such that intelligence is detectable. Field strength or signal power is only half of the story. A poorly designed receive antenna will deny reception of a signal just as though the transmitter had been shut off. A receive antenna in a high noise environment will mask the signal such that no intelligence can be detected. Early work prior to World War II in broadcasting only used the field strength as a measure of communications success. However, since the 1940's radio engineers have used Signal-to-Noise ratio as the preferred measure of communications success. SNR is directly related to intelligence transfer. Also at great expense very accurate RF noise prediction models have been developed for use in computing the SNR. 38

Choosing the correct Sunspot Number I am a of VOACAP or VOACAP-derived software (for instance HamCAP, MultiProp, WinCAP Wizard 3 or ACE-HF). I do not know which of the available sunspot numbers (SSNs) I should use in any of these programs mentioned. Many people and major HF propagation sites suggest using daily or monthly sunspot numbers from the SEC (Space Environment Center,http://sec.noaa.gov/ftpdir/weekly/Predict.txt) or from SIDC, Belgium (http://sidc.oma.be). George Lane: In short, use the smoothed International Sunspot Number (SSN) values in VOACAP -- or in any other interface program that uses VOACAP as their calculation engine. Smoothed SSNs can be found from the National Geophysical Data Center at:ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SUNSPOT_NUMBERS/sunspot.predict. They maintain the (predicted) SSN figures based on the Lincoln-McNish smoothing function. These are the sunspot numbers used in the database reduction for the worldwide ionospheric maps used in IONCAP and now VOACAP. The variation of "daily solar flux" over the days of the month is taken into by VOACAP through the use of the MUF-DAY tables. The trick is to get the circuit MUF predicted correctly using the smoothed International Sunspot Number from the National Geophysical Data Center. This also requires using the CCIR coefficients (same epoch as the F-days tables) and NOT the URSI-88 coefficients (a totally different solar cycle for the foF2 mixed with the old foF1 and foE). Also, the day of the month should not be specified, as this will force the use of the URSI-88 coefficients. Method 26 will show the FOT-MUF-HPF values by hour for the month. That is where you can see the expected variation of the MOFs due to daily variations in the solar flux. I wish we had changed the designation of FOT to 90% of the days and the HPF to 10% of the days, as they represent the lower and upper decile range of the expect MOF values over the days of the month at that hour. To be more elaborate, the solar energy reaching the ionosphere is dependent on the number and size of the sunspots. The effects take two to three days to substantially change the ionization in the ionosphere. The net effect is that on a given HF link the Maximum Observed Frequency (MOF) for the path at a given hour will change over the days of the month. An old rule of thumb was that the MOFs would vary around the monthly median value (MUF) for that hour by ± 15%. In the early 1960's the scientists at ITS in Boulder CO collected a fairly substantial data base over a full solar cycle during the IGY (1958-1963) period. This is what George Haydon wrote in 1966: 

An investigation of the distribution of daily values of Maximum Observed Frequency (the MUF at a given hour and day in the month) about their monthly median was carried out. Three points in the distribution over the days of the month were considered; values of the daily MUF exceeded 0.90, 0.50 and 0.10. These points are now referred to as the optimum working frequency (Frequence Optimum de Travail or FOT), the Maximum Usable Frequency (MUF) and the Highest Probable Frequency (HPF). [Davis, R. M. and N. Groome (1964), Variations of the 3000-km MUF in time and space (private communication)]



Data used in this study was derived from measurements at 13 stations representing a range of geomagnetic latitudes from 71 degrees S to 88 degrees N. The variation in frequency about the MUF was represented in tables of upper and lower decile values for low, medium and high Sunspot Number. Each table showed values for a given season, local time in hours 00, 04, 08, etc., and each 10 degree of geographic latitude from 10 degrees to 80 degrees, north or south.



The study indicated that the distribution of MUFs is wider at night than in the daytime and wider at low latitudes than high latitudes in the daytime. Again in daytime the distribution is wider in summer than winter, except at high latitudes where the reverse is true. The sunspot number dependence is weaker, but in daytime the difference between two ratios seems to increase 39

with sunspot number at latitudes higher than 40 degrees and to decrease with increasing sunspot number at latitudes below 40 degrees. The distribution of frequency variation was mostly a function of the foF2 and not the M(3000)F2 (the factor used to convert the vertical incidence critical frequency to the oblique path MUF); therefore, the distributions are assumed valid for any oblique path. [Davis, R. and N. Groome (1965), The Effect of Auroral Zone Absorption on High Frequency System Loss, (private communication)] [Lucas, D.L. and G. W. Haydon, [1966] Predicting Statistical Performance Indexes for High Frequency Ionospheric Telecommunications Systems, ESSA Technical Report IER 1-ITSA 1.] In 1966, tables of the FOT-MUF-HPF distribution as a function of local time at the transmitter, season, smoothed sunspot number (SSN) and geomagnetic latitude (of the transmit site) were incorporated in the first widely used HF ionospheric radio performance prediction program, ITSA-1 [Lucas and Haydon, 1966]. These are often referred to as the F-Days tables. The value of F-DAY was loosely defined as the probability of ionospheric (i.e. the fraction of the days that the operating frequency is below the MUF). The development of IONCAP changed these definitions, as the F-DAYS values were only used for the lowest order mode for a circuit-hour. This is also called the MUF mode and is very carefully computed using convergence of up to 5 iterations. Modified distributions are assumed for the MUFs about each of the higher order modes (up to 20) depending on the layer; Es, E, F1 and F2 [Lloyd, et al., 1978] [Lloyd, J. L., G. W. Haydon, D. L. Lucas and L. R. Teters, [1978] Estimating the Performance of Telecommunication Systems Using the Ionospheric Transmission Channel; Volume I: Techniques for Analyzing Ionospheric Effects Upon HF Systems {DRAFT}, US Army CEEIA Technical Report EMEO-PED-79-7]. The authors of IONCAP often stated that F-DAYS are not used in IONCAP. However, in VOACAP the "FDay" factor given for each of the defined operating frequencies was changed to show the value actually being used for the most reliable mode (mrm) for that frequency. This new factor is named MUF-DAY in VOACAP [Lane, 2001]. My paper at the Ionospheric Effects Symposium (Alexandria VA, May 3-5, 2005) happens to be ing VOACAP for frequency assignment for ALE links. Rockwell Collins provided me with nearly 22 days of data on a long path from to Cedar Rapids (over 7,000 km). I had a real headache as the data was taken in July 2004 and the International Smoothed Sunspot number kept changing each month until Feb 2005. It takes 6 months for the smoothing function to settle in on a final value! Collins had kept track of the frequency having the highest SNR at each hour for a scan of 20 frequencies. My contention was that ALE systems should follow the circuit MUF as that is where the signal is the strongest. A linear correlation analysis of the measured median best SNR frequency versus VOACAP predicted MUF provided a correlation coefficient (r2) of 86%. That is amazingly high considering the fact that the MUF mode changed from 2F2 during the day to 3F2 at night on that path. I also looked at the correlation between the measured upper decile and lower decile of the frequencies being used per hour with the predicted HPF and the FOT. There was good agreement but not as good as at the MUF. Hope this is helpful in what seems like a never ending discussion of sunspot numbers. By the way, ICEPAC was supposed to be a daily prediction program but it seems that work on the program ended long before it was ready to be released. But that is the topic of my second paper.

VOACAP Predictions at Low Frequencies I find that VOACAP underpredicts s at the lower part of the HF spectrum, say 1.8 or 3.5 MHz. George Lane: Poor George Haydon and John Lloyd (the creators of IONCAP) pulled their hair out when I said IONCAP had to go down to 2 MHz. I knew there are real life situations where 2 MHz is a needed frequency such as in northern , Norway, Alaska, etc. in the winter time. Army radio links were always failing and it wasn't until we got chirp sounders on those links that we found the MUF was going below 3 MHz at 40

night on short paths. George Haydon said there was very little data below 4 MHz but there was some for short paths that did go down to 2 MHz. So they modeled a fit to those cases. Risky, but it has proven to give good results for Near Vertical Incidence Skywave (NVIS) situations. Radio amateurs and SWLs (who like to DX on 1.8 MHz band or pick up signals from very distant MW stations at night) are finding VOACAP does not predict such s at 2 MHz whereas they know that they are making such s. What is happening is that VOACAP is a ray hop model for normal HF skywave propagation and it does not consider the 'wave guide' sort of propagation that occurs with the residual E layer on all dark paths for the medium wave band. John Wang at the FCC has just had his worldwide medium wave prediction model adopted by the ITU-R. I think John Wang's model is excellent and it should be used for medium wave coverage predictions. I would not try mixing it with VOACAP unless you run both models at 1.8 MHz and select the higher signal power. VOACAP is quite good for NVIS and Wang's model is good for long distance MW paths in full darkness. Since ITS delivered IONCAP to the Army in 1978, I have fought to keep IONCAP theory unmodified. VOACAP is a cleaned up and corrected version of IONCAP and it retains all of the theory as put forth by Lloyd, Haydon and Lucas. I don't recommend taking portions of Wang's model to be put into VOACAP. The reason is that both programs are semi-empirical in that the theory has been forced to fit certain measured data but not the same set. From a purely statistical point of view, one should not mix two dissimilar models without redoing the correlation analysis.

Comparing VOACAP, ICEPAC and REC533 One of the problems with the HF software is that they are all based on monthly median data. But what everyone seems to want is "now-casting". George Lane: Let me first address the time discontinuity in the ITS programs VOACAP, ICEPAC and REC533. There are several large global maps of ionospheric data used in these programs. That data was collected during the IGY (the International Geophysical Year, late 50's to early 60's). The data was reduced to tables which were valid for 2 or 3 month periods at the even hour. These maps are the critical frequency for the E, F1, F2, M-3000, F-days distribution and the EXCESS SYSTEM LOSS TABLES (more about them later). Of equal importance to the signal power calculation is the Noise Power. Atmospheric radio noise was mapped in 3 month groups and 4 hour time blocks. The original data on an hourly basis, as collected, is lost. I sitting in with the old Signal Corps Radio Propagation Agency engineers as they discussed whether it is realistic to make computer predictions at each month from tables where the monthly dependence was lost by averaging. I bet their eyes would pop out of their heads if they knew Johnny-come-latelies are now making daily predictions with these averaged models! Certainly, you can force the programs to give a smooth transition across the days of the month but it is just a trick which has little bearing on reality. If you have made HF measurements for as many years as I have, you know that the day to day variations are not smooth across the days of the month at a given hour. However, we can quite accurately compute the distribution of the variation such that we can say only 3 days at this hour during the month should be this bad. But we have no idea when they will occur during the month.

URSI Coefficients and VOACAP Next let's talk a bit e of the URSI Coefficients. Newer is not necessarily better. But the big bug in using them is this. They totally destroy the validity of the EXCESS SYSTEM LOSS TABLES and throw the entire performance prediction process out. Back in the 1950's, the NBS and the RPA discovered that the prediction model just did not predict the signal power that was actually received. There was an 8 dB difference between the median measured power and the predicted power at mid- and low latitude paths. With 90% confidence, the difference jumped up to about 16 dB! Things were even worse at high latitudes. 41

The fix was to create a table of differences at the median, upper and lower decile for predicted versus measured signal power. This was done for one epoch of ionospheric data so that high and low sunspot data was included. This difference table became the EXCESS SYSTEM LOSS TABLE (transmission loss table in IONCAP). It is the fudge factor which brings the prediction signal power down to the level of the measured signal power as a function of path length, geomagnetic latitude, hour, month and sunspot level. John Lloyd, creator of IONCAP, points out very vividly that if you change any of the data base tables to a different epoch, you must recompute the Excess System Loss correction maps. Since the actual data no longer exists, you have no way of doing so. This is why you may get very poor predictions running VOACAP with the URSI coefficients. It could happen that they are really more accurate but it would be a fluke. From a statistician's point of view, you can have no confidence in the performance predictions when using the URSI coefficients which are from a different epoch than the rest of the maps. I can hear someone saying let's use CCIR Data Base D or D-1 or D-2. I attended meetings for the development of Rec.533. I became intrigued when I discovered that they had subtracted 8 dB from the median values in Excess System Loss tables. They only used the residuals of the table less the 8 dB. CCIR never did use any of the decile tables, just the median values. Then they ran REC-533 and subtracted the signal powers from those contained in Data Base D-1. They found the median difference was 9.2 dB. So the net difference was 9.2 - 8.0 or 1.2 dB! Rather amazing since they only use the foF2 maps and compute F-1 and E layer from them. Someone noticed that some of the circuits in DataBase D-1 were greatly different than predictions. So they started removing these offending circuits from the data base. I became very curious because they always seemed to fall in the region of the 1F2 to 2F2 transition. In talking with the German who had processed most of this data, I learned that he had removed the actual antenna pattern gain from the measured signal power by assuming a fix layer height for the F2 layer. Therefore, the normalized data in D-1 was extremely dependent on the nomogram used to assess the takeoff and arrival angle of the signal. This meant that CCIR was forcing Rec.533 to fit the nomogram with a fixed layer height! About the time I retired, CCIR was attempting to 'de-normalize' D-1. Anyhow I have never been too keen on Rec. 533. I especially dislike the use of median values and then applying some variation tables at the end of the prediction. PC's have enough memory and are fast enough today that you don't need all of the simplifications which were needed in the 1980's when most of the Rec.533 development work was done. The intent for 'little 252', HFBC-84 and then Recommendation 533 was to develop a very fast running computer model which could analyze the full International Broadcast frequency schedule on a seasonal basis using inexpensive desk top computers. As such, the development was very forward thinking and successful. There was no way of knowing at that time how fast computer technology would overtake events.

About VOACAP-ICEPAC Comparison There was a recent comment about ICEPAC giving better predictions at long distance on high latitude paths than VOACAP. I have not found that to be true but have had only limited experience. In 1998, I was able to obtain a full month's worth of listener reports here in the USA for the east coast and the west coast on a path nearly over the magnetic pole on a transmission from northern . I had been ed because the broadcaster was using ICEPAC which predicted no usable coverage at any hour. When I ran VOACAP Method 30, I found that the signals should be quite usable on many days in the month. We wrote this up as a paper for the Ionospheric Effects Symposium - 1999 [ John Goodman, chairman. Washington DC ] showing the excellent agreement between VOACAP predictions and actual listener reports for a full month. The reason VOACAP was more 'correct' than ICEPAC is that Method 30 in VOACAP uses a smoothing function between the short path (ray hop) and long (forward scatter) models as a function of distance between 7000 and 10,000 km. ICEPAC uses the abrupt transition between short path and long path at 10,000 km. It turns out that in the ray hop model on that path between and the USA finds an ionospheric control point with a tremendous signal loss whereas the long path model computes a weak but detectable signal 42

assuming a scatter propagation mechanism. Therefore, ICEPAC found no signal and VOACAP found a weak scatter signal which was actually there.

Method 25: Ionospheric Parameters and Semi-thickness What are the definitions of the Method 25 ionospheric parameters? The ionospheric parameters definitions are as follows: YE = LAT LONG HI M3000 HPF2 54.3N 25.6E 0.0 3.19 291.1 45.5N 28.1E 0.0 3.32 273.2 28.6N 31.3E 0.0 3.45 255.6 11.7N 33.6E 0.0 3.16 294.8 2.8N 34.6E 0.0 3.13 299.6 YE HE HS

LMT RAT 6.7 4.2 6.9 3.8 7.1 3.1 7.2 2.9 7.3 2.8

20.0

HE = 110.0

UT E F1 Y1 ZEN ZMAX MAGL 5.0 1.08 0.0 0.0 102.7 73.2 51.9N 5.0 1.70 0.0 0.0 97.6 69.7 42.9N 5.0 2.16 0.0 0.0 87.8 61.0 26.0N 5.0 2.06 0.0 0.0 78.0 52.6 9.0N 5.0 2.16 0.0 0.0 73.2 54.3 0.0N

HS = 110.0

H1

FH/2

F2Z

Y2

H2

ES

MED

0.0

0.6

3.8

71.6

270.9

0.0

0.0

0.0

0.6

4.8

81.1

252.9

0.0

0.0

0.0

0.5

6.1

99.6

292.4

0.0

0.0

0.0

0.4

6.1

99.6

292.4

0.0

0.0

0.0

0.4

6.3 106.1

297.1

0.0

0.0

= YI(1,1) = E layer semithickness of first control point = HI(1,1) = E layer height of maximum ionization of first control point = HS(1) = height of reflection of first control point

The following refer to each of the control points (in this case 5 of them). The number of control points varies with the distance between TX & RX. "k" will be the control point. label LAT LONG LMT UT E F1 Y1 H1 FH F2Z Y2 H2 ES MED HI M3000 HPF2 RAT ZEN ZMAX MAGL

= = = = = = = = = = = = = = = = = = = = = =

variable CLAT(k) CLONG(k) CLCK(k) GMT FI(1,k) FI(2,k) YI(2,k) HI(2,k) GYZ(k) FI(3,k) YI(3,k) HI(3,k) FS(1,K) FS(2,k) FS(3,k) F2M3(k) HPF2(k) RAT(k) ZENANG(k) ZENMAX(k) GLAT(k)

= = = = = = = = = = = = = = = = = = = = = =

definition Latitude of control point Longitude of control point Local mean time UT at transmitter E layer critical frequency F1 layer critical frequency F1 layer semithickness F1 layer height of maximum ionization Gyrofrequency (FH/2 = GYZ(k)/2) F2 layer critical frequency F2 layer semithickness F2 layer height of maximum ionization Sporadic E critical frequency lower decile Sporadic E critical frequency median decile Sporadic E critical frequency upper decile F2 layer M(3000) factor virtual height at 0.834 critical frequency ratio of F2 layer height of maximum ionization to semithickness zenith angle for F1 layer maximum zenith angle for F1 layer geomagnetic latitude

The Sporadic E values in this example are 0.0 because the FPROB variable ("0.0" for Es) removes the sporadic E layer. [Thanks to Greg Hand for explaining these.] What is the term "semi-thickness"? I see it being used in the explanations above.

43

George Lane: It is an old term dating back to the 1940's. Back then they used a set of templates which they would slide over the ionogram based on an assumed parabolic shape to the ionospheric layer of interest. They would find the curve which had the best fit when the template was aligned with the height of the maximum electron density for the layer. The parabolic curve with the best fit was numbered with the semi-thickness (half thickness) of the parabola. It was a term needed to determine the actual ray path as it ed through the various layers. The ionogram plots show electron density as a function of height. It was recognized early on that these plots tended to show the layers as having a parabolic shape. If you consult a geometry text, you will find that there is a locus point for a parabola which is centered on the line where the tangent to the line is vertical. This is the height of the maximum electron density. Each parabola has a width factor associated with the locus point. This is where the line tangent becomes horizontal. By curve-fitting to the ionograms, the scaler was able to find the semi-thickness of the layer based on simple geometry. These parameters are needed in order to determine the amount of bending which occurs as the ray at a particular frequency penetrates the 3 layers. Newer prediction models such as PropLab actually compute the ray path for a particular electron density profile. IONCAP was the first program to attempt this in a quasi-ray trace approach.

3.2 MUF, SNR and REL The MUF and SNR Distribution: Choosing the Best Frequency Understanding Above-the-MUF Predictions Calculating the MUFdays Maintaining the Required Grade of Service: Calculating the Circuit Reliability for a Given Hour

The MUF and SNR Distribution: Choosing the Best Frequency You have now run the prediction and are anxious to operate between the chosen locations on the frequencies you entered. There are two things to discuss in our analysis:  

3.2.1.1

What is the best of our frequencies? What is the predicted SNR (Signal-to-Noise) distribution on that frequency?

The Meaning of MUF

In VOACAP, the MUF (maximum usable frequency) is a statistical concept. The MUF is defined here as the median maximum usable frequency for a given ionospheric path, month, SSN and hour. On each day of the month at this hour, there is a maximum observed frequency (MOF) for a mode. The median of this distribution is called the MUF. Therefore, it is not the maximum usable frequency in of communications. In other words, the MUF is the frequency for which ionospheric is predicted on 50% of the days of the month, ie. 15 days out of 30 days. So on a given day communications may or may not succeed on the frequency marked as the MUF. To ensure a good communication link between two locations, the operating frequency is typically chosen below the predicted MUF. It is often claimed that the optimal operating frequency lies somewhere between 80-90% of the MUF (e.g. if the MUF is 10 MHz, the optimal frequency would be around 8-9 MHz). However, in VOACAP it is the predicted SNR distribution using Complete System Performance methods (e.g. Methods 20, 21, 22 or 30) that determines which frequencies provide an acceptable grade of service.

3.2.1.2

The MUFday

The MUF is also related to another parameter, MUFday. The value of the MUFday is the fraction of the days in a month at that hour that the operating frequency is below the MUF for the most reliable mode (that is, the mode with the highest reliability of meeting the required SNR). The mode and the associated data shown below 44

the -specified frequencies are always the most reliable mode. For a more detailed discussion, seeCalculating MUFdays.

3.2.1.3

SNR, SNR10 and SNR90: The Predicted SNR Distribution

The SNR distribution tells us what grade of service is to be expected over the days in the month on a given frequency at a given hour. A statistical method is used to determine the grade of service over 27 days (SNR90), 15 days (SNR) and 3 days (SNR10) out of 30 days. However, it does not tell you which days are good or which days are bad. Below are the four SNR output parameters needed for analysis: 1.0 13.1 6.1 7.2 9.7 11.9 13.7 F2F2 F2F2 F2F2 F2F2 F2F2 F2F2 80 63 69 78 83 78 26.7 12.4 13.8 21.2 26.7 26.8 18.5 7.6 7.1 7.8 12.7 22.2 54 51 55 57 56 51

15.4 F2F2 68 26.8 25.7 41

17.7 F2F2 28 26.8 25.7 1

21.6 25.9 F2F2 F2F2 -39 -58 26.8 13.3 25.7 7.6 -66 -71

0.0 -

0.0 -

FREQ MODE SNR SNR LW SNR UP SNRxx

The SNR indicates the dB-Hz value that can be maintained on 50% of the days (ie. on 15 days) in the month. In our example above on 11.9 MHz, the SNR value is 83 (dB-Hz). The SNRxx (ie. SNR90, provided the REQ.REL. is 90%) indicates the dB-Hz value that can be maintained on 90% of the days (ie. on 27 days) in the month. In our example above on 11.9 MHz, the SNRxx value is 56 (dBHz). This can be calculated as SNR - SNR LW (or 83 - 27 = 56 in our example). And finally, the SNR10 (calculated as SNR + SNR UP) is the dB-Hz value that can be maintained on 10% of the days (ie. on 3 days) in the month. In our example above on 11.9 MHz, the SNR10 value is appr. 96 (dBHz). The two most prominent parameters to consider in search of the best frequency are the SNR and SNR90 values. As a rule of thumb, look for the highest SNR value and the highest SNR90 value. Let us assume that the required SNR we wish to maintain in our circuit is 67 (not a good but still a reasonable listening quality in international broadcasting). We will see that the SNRxx is below 67 at all our frequencies which means none of them cannot maintain that grade of service on 27 days out of 30 days. Then we will need to look for the highest SNR. Of our frequencies, the best would be 11.9 MHz with the SNR value of 83. Conclusion In conclusion, 11.9 MHz is the best candidate for the operating frequency at 01 UTC during that month. 11.9 MHz is also below the predicted MUF of 13.1 MHz for that mode.

3.2.1.4

The RPWRG and the REL

Let us expand our example above by adding two other output parameters (RPWRG and REL) as follows: 1.0 13.1 6.1 7.2 9.7 11.9 F2F2 F2F2 F2F2 F2F2 F2F2 80 63 69 78 83 13 16 12 10 11 0.74 0.24 0.57 0.74 0.78 26.7 12.4 13.8 21.2 26.7 18.5 7.6 7.1 7.8 12.7 54 51 55 57 56

13.7 F2F2 78 16 0.70 26.8 22.2 51

15.4 F2F2 68 26 0.51 26.8 25.7 41

17.7 F2F2 28 66 0.03 26.8 25.7 1

45

21.6 F2F2 -39 133 0.00 26.8 25.7 -66

25.9 F2F2 -58 138 0.00 13.3 7.6 -71

0.0 -

0.0 -

FREQ MODE SNR RPWRG REL SNR LW SNR UP SNRxx

The RPWRG is related to the SNR90 and REQ.SNR. In our example above, the REQ.SNR was set to 67. The RPWRG (the required power gain) parameter tells us how many desibels are needed in the communication system to achieve the SNR90 value of 67. It is calculated as REQ.SNR - SNRxx (or 67 - 56 = 11 on 11.9 MHz). As the value of the RPWRG is positive in our example, it means that many desibels are needed for our system; if the value had been negative, that many desibels would have been in excess (ie. unnecessary) to achieve the required SNR for 27 days out of 30 days. This parameter relates to the (communication) system design. In our example on 11.9 MHz, we should consider what measures we could take to add the necessary 11 desibels to the system: doubling the transmitting power would give us 3 desibels, using a more powerful transmitter antenna could give us a few desibels more, and at the receiving end we could choose, say, a 3-element Yagi instead of the whip antenna which would still contribute some more desibels. The REL is related to the SNR and REQ.SNR, and is defined as a circuit reliability factor. It tells us the percentage of days in the month when the SNR value will equal to or exceed the REQ.SNR. The SNRxx tells us which SNR value can be achieved on 90% of the days (27 days) in the month. If the SNRxx would have been 67, then the value of REL had been 0.90 (or 90%, which is the REQ.REL. we have specified) and the RPWRG would have been zero (0).

Conclusion The REL value of 0.78 on 11.9 MHz suggests that the required SNR of 67 can be achieved on 78% of days in the month. To translate the percentage value to the number of days, take a look at the Z Tables. We will see that 78% equals to 23 days. For a more detailed discussion on how the REL value is calculated, see the article Maintaining the Required Grade of Service.

Understanding Above-the-MUF Predictions 3.2.2.1

Is it possible to operate above the predicted MUF?

George Lane: The old rule was that if you went above the MUF, no signal propagated back to earth. Measurements have shown that if the signal power is strong enough, you can get a return signal on the earth at frequencies above the MUF. The loss becomes very great as the difference between the operating frequency and the MUF [Foperating - MUF] becomes large. The measured data showed that the availability of blobs of higher electron density fell off at the normal distribution rate with respect to the afore mentioned difference between operating frequency and MUF. The MUF is the middle value of the daily variations of MOF at that hour so it might only occur once in the month! We really need to think about the MOF (hourly median maximum observed frequency on a single day). For frequencies below the MOF we have spectral reflection of the wave from the ionospheric layer. At the MOF itself, the low ray and the high ray add for 3 dB enhancement (this is called the junction frequency). As we go above the MOF, the ray penetrates deeper into the ionosphere. Here in the upper regions of the ionosphere there exists blobs of ionized gases. As the ray es through a blob, it is slightly bent. After ing through enough blobs it is reflected back toward the earth. This is called the Above-the-MUF mode. Just above the MOF the loss is not too much more than spectral reflection. But as the operating frequency is higher than the MOF, the losses go up exponentially as there are fewer and fewer blobs with sufficient electron density to bend the ray. Eventually as the frequency goes higher and higher all of the energy penetrates the ionosphere and is lost. In VOACAP the Above-the-MUF loss is limited to 25 dB. Personally, I think it is too low and probably should be allowed to go to 40 to 50 dB. 46

So what is VOACAP doing? It is computing the distribution of the MOFs over the days of the month. MUFDAY tells you the fraction of the days for which the operating frequency is below the MUF. For those days which are Above-the-MUF, Above-the-MUF losses are included. You will see the SNR LW getting larger and larger as the operating frequency approaches the MUF. As you go above the MUF, SNR LW approaches 27 dB which is a function of that 25 dB limit, I mentioned before. If you only need a few days per month to meet your REQ SNR, then you may well be able to work frequencies at or above the MUF. But if you require REL = 90%, then SNR LW comes into play and the SNRxx is much lower.

3.2.2.2

Good SNR and REL predictions above the MUF

Let us consider the example below. VOACAP predicts good values of SNR and REL at 13.7 MHz and 15.4 MHz. However, the MUFday is 0.38 and 0.12 respectively. So, is it feasible to operate on those frequencies? Dec 2001 SSN = 110. Minimum Angle= 3.000 degrees YLE PORI JOHANNESBURG AZIMUTHS N. MI. KM 61.47 N 21.58 E - 26.25 S 28.00 E 174.24 356.94 5275.6 9769.6 XMTR 2-30 REC705 #01[hfcc\HFBC_218.P15 ] Az=160.0 OFFaz= 14.2 350.000kW RCVR 2-30 2-D Table [default\SWWHIP.VOA ] Az= 0.0 OFFaz=356.9 3 MHz NOISE = -145.0 dBW REQ. REL = 90% REQ. SNR = 67.0 dB MULTIPATH POWER TOLERANCE = 10.0 dB MULTIPATH DELAY TOLERANCE = 0.050 ms 1.0 13.1 F2F2 4.0 12.0 34.4 360 0.50 142 44 -87 -167 80 13 0.74 0.00 0.35 25.0 17.7 26.7 18.5 19.7 -0.9 54

6.1 F2F2 7.6 7.6 34.2 290 1.00 146 35 -90 -153 63 16 0.24 0.00 0.19 9.7 4.9 12.4 7.6 21.9 -2.1 51

7.2 F2F2 7.8 7.8 34.2 297 0.99 143 39 -87 -156 69 12 0.57 0.00 0.28 11.2 4.9 13.8 7.1 21.9 -1.9 55

9.7 F2F2 3.3 3.3 33.9 314 0.95 142 48 -84 -162 78 10 0.74 0.64 0.34 19.2 6.2 21.2 7.8 18.3 -7.0 57

11.9 F2F2 4.0 12.0 34.3 332 0.73 138 47 -83 -165 83 11 0.78 0.00 0.38 25.0 11.6 26.7 12.7 19.7 -0.9 56

13.7 F2F2 4.0 12.0 34.6 387 0.38 145 41 -90 -168 78 16 0.70 0.00 0.33 25.0 21.5 26.8 22.2 19.7 -0.9 51

15.4 F2F2 7.8 22.0 35.2 466 0.12 157 29 -102 -169 68 26 0.51 0.00 0.23 25.0 25.0 26.8 25.7 21.8 0.0 41

17.7 F2F2 7.8 4.0 34.6 402 0.01 198 -5 -143 -171 28 66 0.03 0.00 0.03 25.0 25.0 26.8 25.7 21.8 -5.4 1

21.6 F2F2 7.8 8.0 35.5 574 0.00 268 -77 -212 -173 -39 133 0.00 0.00 0.00 25.0 25.0 26.8 25.7 21.8 -1.8 -66

25.9 F2F2 7.8 7.8 34.9 458 0.00 289 -96 -233 -176 -58 138 0.00 0.00 0.00 9.1 4.9 13.3 7.6 21.7 -1.9 -71

0.0 -

0.0 -

FREQ MODE TANGLE RANGLE DELAY V HITE MUFday LOSS DBU S DBW N DBW SNR RPWRG REL MPROB S PRB SIG LW SIG UP SNR LW SNR UP TGAIN RGAIN SNRxx

George Lane: The MUF = 13.1 MHz at that hour. So a broadcast frequency of 13.7 is only a little bit above the MUF. At least 38% of the days will be below the MUF (MUFday = 0.38) and reception will be great. On 62% of the days reception will be not-so-good to terrible... So on almost half of the days of the month propagation will be just great. That is why the median SNR should be high. So then, how about 11.9 MHz? 13.7 MHz is only 70% reliable (REL = 0.70) whereas 11.9 is 78% reliable (REL = 0.78). At the median, the Signal-to-noise ratio (SNR50) at 11.9 MHz is 5 dB higher than at 13.7 MHz. Clearly there is about 1 S-unit advantage to using 11.9 MHz band over that of the 13.7 MHz band on at least half of the days of the month. Also on the bad days of the month, 11.9 will work better than 13.7 MHz so that is another advantage. I fear at 15.4 MHz, you are getting into the noise of the program. By that I mean, VOACAP will give predictions even when it has no idea what is going to happen. One would normally stay away from using this frequency for this reason: 47

SNR10 = 94 dB-Hz SNR50 = 68 dB-Hz SNR90 = 41 dB-Hz

If we believe the prediction, then VOACAP is saying that 80% of the days of the month (bounded by SNR90 and SNR10) will have a SNR somewhere between 41 and 94 dB-Hz. That is a spread of 53 dB or a factor of 200,000! If the program could talk, it would tell you that it doesn't have any idea what is going to happen on 15.4 MHz. At best you can say there is a 12% (MUFday = 0.12) chance of good service and 88% chance it will be less than good. There is one more variable that one should look at when dealing with frequencies way above the MUF. That is the Signal Power at the receiver, S PWR (aka S DBW). Often you will find that the power is actually at or below the receiver threshold. In that case the receiver thermal noise becomes controlling and the grade of service is much less than the SNR would indicate. In our example, 15.4 MHz has a predicted S PWR of -102 dBW. If we assume the receiver input impedance is 50 Ohms and that the transmission lineloss is minimal, then the median voltage at the input of the receiver is -102 + 137 or 35 dB relative to 1 microvolt, or 56 uV (see [1] below; see also: S DBW to S Meter Correlation Table). For a good receiver this is an adequate input voltage. But if we impose a desired reliability of 90%, the signal power reaching the receiver is -102 dBW - 25 dB (SIG LW) = -127 dBW. Using the previous logic, then the voltage at the receiver under ideal conditions is only 3 uV. For most receive systems which have antenna efficiency, transmission line and impedance mismatch losses, this signal voltage does not overcome thermal noise even in a good commercial receiver. If you look at S PWR at 17.7 MHz, you will find that the voltage at the input of the receiver has dropped to 0.5 uV which would require a very expensive receiver with good sensitivity and little impedance mismatch loss between the antenna and the receiver.

Conclusions VOACAP makes the assumption that the external RF noise power is controlling. At high frequencies where the signal power and the noise power become very low, this assumption may fail. If we only look at the SNR, we may be fooled into thinking the grade of service will be good when in fact the receiver noise is greater than the signal plus external noise power.

The authors of IONCAP (the parent program for VOACAP) always warned us that we should only believe the predictions when the reliability was approximately 90% or higher. In your example, if I were the frequency planner for that broadcast, I would select 11.9 MHz as the best frequency. But I still would expect that on some days transmissions on 15.4 MHz will come booming in. The chances that transmissions on 17.7 MHz will be heard on any day of the month depends greatly on the receiver and its antenna. So the conclusion is that reception on frequencies which are above the predicted MUF are certainly possible and in some cases reception will be possible on more than 15 days of the month at that frequency.

3.2.3.1

[1] Equations to Calculate The Median Voltage at the Input of the Receiver

Ohm's Law: E = I*R or I = E/R

Power formula: P = EI

48

P is in Watts, E is in Volts and I is in Amps and R is in Ohms. Then: P = E * [E/R] = (E^2)/R

Solve for Voltage: E^2

= [P*R]

Convert to dB: 10 Log E^2 = 20 Log E = 10 Log [P*R]

Express E in of microVolts such that E(V) = E (uV) x 10^6, then: 20 Log E + 20 Log [ 1V / 10^6] E(dBuV) - 120

=

=

10 Log [P*R]

10 Log P + 10 Log R

Assume R = 50 Ohms: E(dBuV) - 120 E(dBuV) =

=

10 Log P

+ 10 Log (50 Ohms) = P(dBW) + 17

P(dBW) + 17 + 120 = P(dBW) + 137

Finally, E in uV is 10^(dBuV/20) or antilog [(dBuV)/20]. Example: 35 dBuV = 10^(35/20) = 56 uV.

Note VOACAP computes the signal power [S DBW] which is equivalent to the P(dBW) in the above equations. DO NOT confuse the predicted field strength in the VOACAP output, DBU (dB relative to 1 microVolt per meter), with the voltage at the receiver as given by dBuV (dB relative to 1 microVolt) in the above equations.

Calculating the MUFdays Let us elaborate the concept of the MUFday by examining how the MUFday factor is being calculated.

3.2.4.1

Running HPF-MUF-FOT graph

First we need to run Method 9, HPF-MUF-FOT graph, for our circuit. We are interested in the frequencies at 01 UT (= GMT). Below are the MUF, FOT and HPF values from Method 9: GMT

MUF

FOT

HPF

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0

13.1 12.2 11.6 12.1 15.1 21.4 29.4 25.2 26.3 36.5 35.0 34.0 33.0 31.4 28.5 24.5

10.5 9.8 9.2 9.6 12.7 18.0 24.7 22.4 23.4 31.7 30.4 29.5 27.8 26.4 23.9 20.6

15.6 14.5 13.8 14.4 17.5 24.8 34.1 28.2 29.4 40.5 38.8 37.7 36.0 34.2 31.1 26.7

49

17.0 18.0 19.0 20.0 21.0 22.0 23.0 24.0

20.4 17.4 15.4 14.1 13.0 12.8 13.1 13.5

17.6 14.9 13.3 12.1 10.8 10.6 10.9 11.2

24.5 20.8 18.5 16.9 15.5 15.2 15.6 16.0

The HPF, FOT and MUF represent the Highest Possible Frequency, Optimum Working Frequency (or Frequency of Optimum Traffic) and Median Maximum Usable Frequency, respectively, for the hourly MOF (median maximum observed frequency) distribution. At the HPF, communication can be ed on 10% of the days (3 days) in the month; at the FOT, 90% of the days (27 days) in the month and, as discussed above, at the MUF, 50% of the days (15 days) in the month.

A Rule of Thumb The practical meaning of FOT and HPF [As obtained from Method 9 in VOACAP] is that they determine the frequency range within which we should find80% of the measured MOFs.

3.2.4.2

Two formulas for calculating the Z value

For calculating the fraction (z) of days where we can expect our operating frequency (FREQ) to be below the MUF we have two formulas: one for cases when the FREQ is equal to or below the predicted MUF (1), and the other for cases when the FREQ is above the predicted MUF (2). (1) z = (MUF - FREQ) / ((MUF - FOT) / 1.28) (2) z = ABS(MUF - FREQ) / (ABS(MUF - HPF) / 1.28)

Let us choose two frequencies 9.7 and 13.7 MHz for our calculations. 9.7 MHz is below the predicted MUF so we choose the formula 1: (1) z = (13.1 - 9.7) / ((13.1 - 10.5) / 1.28) = 3.4 / 2.03125 = 1.674.

3.2.4.3

Converting Z to days

To convert the Z to a percentage value and corresponding number of days, let us look at the Z Tables, Table 1: just over 95% or 28 days. Then for 13.7 MHz, above the predicted MUF, we choose the formula 2: (2) z = ABS(13.1 - 13.7) / (ABS(13.1 - 15.6) / 1.28) = 0.6 / 1.953125 = 0.3072,

corresponding to approximately 38% or 11 days (see Table 2). To confirm these values, below you see that VOACAP has calculated the same values for those two frequencies (0.95 = 95% and 0.38 = 38%): 1.0 13.1 6.1 7.2 9.7 11.9 13.7 15.4 17.7 21.6 25.9 F2F2 F2F2 F2F2 F2F2 F2F2 F2F2 F2F2 F2F2 F2F2 F2F2 0.50 1.00 0.99 0.95 0.73 0.38 0.12 0.01 0.00 0.00

50

0.0 -

0.0 FREQ - MODE - MUFday

Maintaining the Required Grade of Service: Calculating the Circuit Reliability for a Given Hour Let us assume you wish to know on how many days in a month a certain grade of service can be maintained on a given hour between two locations. The grade of service is expressed in VOACAP by the parameter REQ.SNR (the required signal-to-noise ratio in dB-Hz). This is a critical setting that must be considered carefully. The correct value to select is dependent on the transmission mode, and the reception quality we like to maintain. As a rule of thumb, a reasonable listening quality in the AM mode can be maintained by using the REQ.SNR value of 67, for CW the REQ.SNR can be, say, 27 and for SSB, 45. always to set REQ.REL. to 90%.

3.2.5.1

The Basic Formulas

For this exercise, you will need two formulas for calculations. The formula 1 is for cases where your REQ.SNR is lower than the predicted SNR, and the formula 2 for cases where your REQ.SNR is greater than the predicted SNR. The formulas 1 and 2 will calculate the parameter z. As such, the parameter z has no meaning; you will need to use the Z Tables to translate it to a probability (%) value and to the corresponding number of days in a month. Also you need to run VOACAP to get the values of SNR, SNR LW and SNR UP for your circuit. When your required SNR (REQ.SNR) is equal to or less than the predicted SNR, use the following: (1) z = (SNR - REQ.SNR) / (ABS(SNR LW) / 1.28) When your required SNR (REQ.SNR) is greater than the predicted SNR, use the following: (2) z = ABS(SNR - REQ.SNR) / (ABS(SNR UP) / 1.28)

1. Case Scandinavian Weekend Radio Calculate the number of days in December 2001 that Scandinavian Weekend Radio (Virrat, Finland) can be heard in Copenhagen (Denmark) at 1800 UTC at the REQ.SNR level of 67. The frequency is 6170 kHz, and the monthly smoothed sunspot number (SSN) is expected to be 110. SWR uses a 100-watt transmitter with a horizontal half-wave dipole (beamed at 150 degrees) at 8 meters above the ground. The receive antenna in Copenhagen is the default shortwave whip antenna, SWWHIP. This is what we get as a result from VOACAP by running the circuit (Method 20): Dec 2001 SSN = 110. Minimum Angle= 3.000 degrees VIRRAT COPENHAGEN (KOBENHAV AZIMUTHS N. MI. KM 62.38 N 23.62 E - 55.72 N 12.57 E 225.33 35.83 524.2 970.7 XMTR 2-30 IONCAP #23[omat\48-8m.ant ] Az=150.0 OFFaz= 75.3 0.070kW RCVR 2-30 2-D Table [default\SWWHIP.VOA ] Az= 0.0 OFFaz= 35.8 3 MHz NOISE = -145.0 dBW REQ. REL = 90% REQ. SNR = 67.0 dB MULTIPATH POWER TOLERANCE = 10.0 dB MULTIPATH DELAY TOLERANCE = 0.050 ms 18.0

6.8 1F2 35.9 4.2 392 0.50 123 20 -104 -158 54 36

6.2 1F2 29.6 3.9 308 0.76 119 23 -101 -157 56 30

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

51

0.0 -

0.0 -

0.0 -

0.0 -

FREQ MODE TANGLE DELAY V HITE MUFday LOSS DBU S DBW N DBW SNR RPWRG

0.06 0.00 0.11 20.3 9.4 22.2 10.9 -2.5 -0.7 31

0.04 0.00 0.12 17.1 5.4 19.4 7.8 -4.6 -0.3 37

-

-

-

-

-

-

-

-

-

-

REL MPROB S PRB SIG LW SIG UP SNR LW SNR UP TGAIN RGAIN SNRxx

Please note that for the circuit calculation we have assumed some power losses so that only 70% of the transmitting power goes to the antenna. That explains the power of 0.070kW in the above example. The same "70% rule" applies to our second example below. As we can see, the required SNR (67) is greater than the predicted SNR (56) for that hour. The poor performance of this circuit is mainly due to the low transmitting power. Furthermore, the broadcast frequency (6.17 MHz, or 6.2 as given above) is too close to the MUF (6.8 MHz). The MUF is defined as the median maximum usable frequency for a given path, month, SSN and hour. On each day of the month at this hour, there is a maximum observed frequency (MOF) for this mode (1F2). The median of this distribution is called the MUF for that mode. In other words, the MUF is the frequency for which ionospheric is predicted on 50% of the days of the month. The required SNR is greater than the predicted SNR, so we need to use the formula 2: (2) z = ABS(SNR - REQ.SNR) / (ABS(SNR UP) / 1.28) where z = ABS(56 - 67) / (ABS(7.8) / 1.28) = 1.805 Now, look up the z value of 1.805 in Table 2. The percentage value will be around 3.6% which corresponds to just about 1 day. By the way, if the power to the antenna would have been 100 watts instead of 70 watts, we could have got 7% (2 days) as the result. Looking back now to the circuit results, you will see that the value of REL, the Circuit Reliability Factor, is 0.04, ie. 4%. This is the same answer VOACAP gives us without any laborous calculations from our part! This is the SNR distribution as a chart:

The Answer If the required SNR is 67, then the circuit reliability is predicted to be about 3.6% (REL 0.04 ie. 4%). That means you can maintain a reasonable grade of broadcasting service between Virrat and Copenhagen only on one day out of 30 days in December 2001 on the frequency of 6170 kHz at 1800 UTC. 52

2. Case YLE Radio Finland In December 2001, YLE Radio Finland transmits from Pori (Finland) to Africa on 15.520 MHz with a transmitter power of 500 kW between 17-18 UTC. Calculate the number of days in a month to achieve a 67-dB circuit reliability at these hours in Johannesburg (South Africa). This circuit is almost 10,000 kms so we are using Method 30, Short/Long Path Smoothing: Dec 2001 SSN = 110. Minimum Angle= 3.000 degrees YLE PORI JOHANNESBURG AZIMUTHS N. MI. KM 61.47 N 21.58 E - 26.25 S 28.00 E 174.24 356.94 5275.6 9769.6 XMTR 2-30 REC705 #01[hfcc\HFBC_218.P15 ] Az=160.0 OFFaz= 14.2 350.000kW RCVR 2-30 2-D Table [default\SWWHIP.VOA ] Az= 0.0 OFFaz=356.9 3 MHz NOISE = -145.0 dBW REQ. REL = 90% REQ. SNR = 67.0 dB MULTIPATH POWER TOLERANCE = 10.0 dB MULTIPATH DELAY TOLERANCE = 0.050 ms 17.0 20.4 F2F2 7.0 14.0 35.0 462 0.50 143 47 -87 -172 85 9 0.81 0.00 0.40 25.0 20.4 26.7 21.2 21.8 -0.5 58

15.5 F2F2 7.2 7.2 34.1 281 0.87 140 49 -85 -167 83 2 0.88 0.00 0.47 15.1 5.5 17.5 7.2 21.9 -2.4 65

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

FREQ MODE TANGLE RANGLE DELAY V HITE MUFday LOSS DBU S DBW N DBW SNR RPWRG REL MPROB S PRB SIG LW SIG UP SNR LW SNR UP TGAIN RGAIN SNRxx

Now the REQ.SNR is lower than the predicted SNR (83) so we'll apply (1) z = (SNR - REQ.SNR) / (ABS(SNR LW) / 1.28) where z = (83 - 67) / (ABS(17.5) / 1.28) = 1.17 The z value of 1.17 (now from Table 1) translates approximately to 88%, which corresponds to 26 days. Again, we will note that VOACAP has already calculated the same value for us in REL (0.88 = 88%). 18.0 17.4 F2F2 4.0 12.0 34.4 350 0.50 143 45 -87 -170 83 11 0.77

15.5 F2F2 4.0 12.0 34.2 317 0.84 137 51 -81 -168 87 7 0.83

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

0.0 -

53

0.0 -

0.0 -

0.0 -

0.0 -

FREQ MODE TANGLE RANGLE DELAY V HITE MUFday LOSS DBU S DBW N DBW SNR RPWRG REL

0.00 0.37 25.0 20.9 26.7 21.6 19.7 -0.9 56

0.00 0.42 25.0 9.5 26.6 10.8 19.7 -0.9 60

-

-

-

-

-

-

-

-

-

-

MPROB S PRB SIG LW SIG UP SNR LW SNR UP TGAIN RGAIN SNRxx

Here, z = (87 - 67) / (ABS(26.6) / 1.28) = 0.962, which is approximately 83% or 25 days (see Table 1). Note again the REL of 0.83 (83%) given by VOACAP.

The Answer YLE Radio Finland is predicted to maintain a reasonable grade of broadcasting service to Johannesburg (South Africa) on 26 days out of 30 days in December 2001 on the frequency of 15.520 MHz at 1700 UTC, and on 25 days out of 30 days at 1800 UTC.

3.3 Signal Power & Noise Power Summing Signal Power from Multiple Modes Calculating the Received RF Noise Power

Summing Signal Power from Multiple Modes How does VOACAP handle the calculation of the signal power as the signal can arrive in multiple modes? George Lane: It helps to see what is happening when looking at all modes output (Method 25) of VOACAP or ICEPAC. VOACAP is attempting to compute the hourly median signal power values for the 30 days in the month at that hour and SSN. It does this for up to 21 different possible modes [ e.g. 2F2, 3F2, 4F2, 2F1, 3F1, 4F1, 4E, 5E and 6E for the high ray and the low ray modes plus the 4Es, 5Es and 6Es for a total of 21 ]. For each of the possible modes, the program computes the monthly median and the power levels which should be exceeded on 27 days of the month and on 3 days per month (lower and upper decile). Again , these are predictions of the hourly medians at a given hour over the days of the month and not what is happening during a single hour of one day. It is assumed that the presence of multiple modes will increase the available power over the days of the month compared to what any individual mode might contribute by itself. The calculation process is very simple. The signal power in dBW is converted to Watts and the values are added to obtain the combined signal power. The sum is then computed as dBW. This process is done for the median signal power and the upper and lower decile signal powers to give the monthly distribution. Usually, the contribution of secondary modes to the monthly distribution of hourly median signal powers is not much but may be 4 to 6 dB. This happens usually when the antenna patterns a secondary mode better than the primary mode (a bad design situation but very common). In practical , the program is attempting to cover what really happens. I have had the opportunity to be making signal power measurements on paths where there was an oblique ionospheric sounder. Some days the 1F2 mode would be stronger but on other days when the 2F2 MUF would rise sufficiently, that mode would be stronger. When we look at the distribution of the signal powers at that hour over the 30 days of the month, the 2F2 mode occasionally provided a stronger signal than the 1F2. This means that 2F2 mode improved the performance of the circuit than if we only had the 1F2 mode. So the presence of other modes which become stronger than the most reliable mode on some days, will enhance the signal power available than if we had only the single mode by itself. 54

I think people get confused about the prediction process. They think that the mode contributions are being added for a single day in the month which doesn't make much sense. We all know that multiple modes at a given instant can cause harmful multipath which does NOT improve the circuit performance. What the program is doing is saying that on the days when the primary mode is weak, is there another mode which may come into play? If so, then the monthly distribution of signal powers is higher than if no other mode is available. Another problem is that many people think in of field strength measurements where the antenna for field strength meter combines all of the incoming signals into one field strength reading. VOACAP is based on signal power measurements at the receiver and not field strength measurement. VOACAP computes the power of each arriving ray path using the appropriate antenna patterns for that takeoff or arrival angle. The summing process of the individual mode contributions to obtain a combined power distribution for an hour over the days of the month is forced to fit actual measurements by applying the Transmission Loss Table (Table 7) in the IONCAP theory manual. There is no theoretical justification for adding the signal powers of the various modes to obtain the combined signal power distribution. But there is good agreement with measurement which is what this program is all about. If you look at Method 25 output, you will see that the contribution of the other modes is not very much over that of the most reliable mode by itself. But these are the small adjustments in the prediction process that has made the IONCAP family of programs better than the older or simpler models. By the way, the IONCAP family of programs does have a multipath probability calculation which is supposed to give an estimate of the probability that the presence of other modes will cause serious multipath conditions. Sadly, this calculation is in error. However, funding ran out before I could get the corrections into VOACAP.

Calculating the Received RF Noise Power I have a high-gain receive antenna and I am puzzled because it seems that its power gain is simply ignored in the calculation of the noise power! I thought the antenna gain would affect both the received signal power and the noise power equally. George Lane: Yes, the gain of your receive antenna is indeed ignored in the calculation of the noise power. The noise power is computed from the CCIR radio noise model where the noise power is assumed to arrive from all directions equally. The use of the theoretical short lossless whip (1/32nd of a wavelength) was to give slightly higher noise for the lower arrival angles. The main assumption here is that any antenna over ground has an average gain factor of 2 since all power directed into the ground plane is reflected back into the upper half space. Thus if the noise arrives from all angles equally, any antenna will produce approximately as much noise power at the receiver as the short lossless whip. However, if the antenna is loaded and has a resistive loss, then that loss must be removed from the noise power as well as the received signal power. Rhombics and terminated vee antennas are examples where the efficiency factor of the antenna must be subtracted from the CCIR noise power. [Note: the power gain values in the Method 13 and 14 tables include the efficiency loss] Short vertical antennas such as whips and inverted-L antennas also have an efficiency loss which is attributed to resistive losses in the ground plane. You can see these values by running a short fixed length monopole using Method 14. The efficiency values are printed at the bottom of the gain table. Antennas such as horizontal dipoles, yagi, log periodic antennas are assumed to have no efficiency losses. By the way, this is a bad assumption when the dipole element is closer than 1/16th wavelength over the ground. At that point, ground losses begin to show up in the input impedance of the antenna and are a real resistive loss! What about the SWWHIP receive antenna that produces less noise power than an isotrope? In the SWWHIP file we can see that an efficiency factor of -4.8 dB has been applied.

55

George Lane: Basically, you need to integrate the power gain pattern of the antenna in the half space over the ground. This is often called the 'average' gain of the antenna. If the gain factor is 2, then the efficiency is 0 dB. In the case of my shortwave whip model (based on actual measurements of a 15 ft. whip antenna over a ground plane with 15 radials of 15 ft. each at 2 MHz in 1943 at Ohio State University [classified SECRET at the time]), the average gain is 0.331 rather than 2 (10Log(0.331) = -4.8 dB). This value is subtracted from the received noise power, only. The gain pattern of the antenna is applied to the signal power at the appropriate arrival angles.

3.4 Antennas & Radiation Angles Method 15, or Transmitter & Receiver AntennaPatterns VOACAP Angle Predictions Minimum Angle in VOACAP Predicting the Takeoff Angle Parameter TANGLE

Method 15, or Transmitter & Receiver AntennaPatterns I am learning VOACAP and have questions about Method 15. It is said that we should always compute the antenna patterns with Method 15 when we are analyzing a circuit for the first time. George Lane: It is not necessary to run Method 15 in order to obtain valid circuit predictions. However, it is necessary to input the antenna data correctly in order to obtain valid circuit predictions. It is very easy to generate a wrong antenna pattern and it is very difficult to determine that the antenna pattern is wrong when you are just looking at the circuit predictions. Therefore, I recommend that s always run Method 15 when beginning an analysis to make sure the pattern for the transmit and receive antennas look reasonable for the antenna you are trying to model. The pattern is shown as a table of gain values in dB relative to an isotrope in free space for the great circle route azimuth defined by the geographic coordinates you specified for the transmit and receive locations. The pattern is shown by elevation angles with 0 degrees being along the horizon and 90 degrees being straight up (y-axis) and by frequencies from 2 to 30 MHz (x-axis). For example, if you are modeling a horizontal dipole antenna at one quarter wave length above ground, you would expect to see the maximum gain of 5 to 8 dBi at the high elevation angles and negative gain values at the low elevation angles. Also the pattern should be relatively constant from frequency to frequency across the table. I cannot understand the meaning of "off-azimuth". George Lane: When you input the antenna data, you must specify an antenna azimuth or select "at" the transmit or receive site. If you specify an azimuth, then the program will determine the difference between the great circle route azimuth and the one you specified. Then the pattern will be computed for that many degrees from the mainbeam azimuth for that antenna. For some antennas which are omnidirectional, one can ignore the off-azimuth. The isotrope, whip and discone are some examples of omni-directional antennas. The antennas do have a real azimuth and that should be entered into VOACAP. that VOACAP uses azimuths relative to True North. Often the azimuth of the antenna as built is specified in of Magnetic North as obtained from a com reading. You will need to correct magnetic azimuths to true north azimuths using the correct declination angle for that geographic location. It is difficult to visualize the antenna patterns, as Method 15 gives only textual, not graphical, results. George Lane: When you want to generate an antenna pattern for the antenna of interest, you should use HFANT. With HFANT you can see the pattern plotted out on a graph. When you have obtained patterns that you feel represent the antenna in question, be sure to name the antenna and save it in your antenna folder. Then 56

when you run VOACAP, you can pull that antenna design from your antenna file. I still recommend that on the first run for that circuit, you run Method 15 just to make sure the right patterns are being called. I being called by an individual who was getting very poor predictions on a path that should have worked very well with a horizontal dipole antenna. After much work, I noticed the dipole was nearly 90 degrees off-azimuth! It seems he thought the mainbeam azimuth of the dipole was the direction of the wire and not broadside to it. If he had run Method 15, he would have soon discovered that the dipole was not working the way it should. I have calculated MUF, SNR, etc. without calculating the antenna pattern with Method 15. Is this fatal to the results? George Lane: NO. The MUF is dependent on the circuit, time of day, month and sunspot number and is independent of the antenna, transmitter power, etc. But, SNR, REL, RPWRG, Sig PWR, and DBU are dependent on the system parameters which include the antenna patterns.

VOACAP Angle Predictions I feel that the arrival angle predictions made by VOACAP are not so well founded empirically as, for example, the predictions of signal strength. George Lane: You are absolutely correct about the takeoff and arrival angle calculations in VOACAP. They are fixed values for simple ray hops. Exotic modes such as N and M are ignored, too. The reason is that there was no measured data which would provide a statistical representation of the angle distribution. Around 1990, Dr. Leo McNamara invited me to see a demonstration of the SkyLoc system which had been set up at the FCC HFDF site here in Columbia, MD. This system provided full angle of arrival data which was sampled at a very rapid rate. What amazed me was that the data collected over 5 minutes or so was showing strongest signals at arrival angles spanning 10 to 30 degrees and with a azimuthal spread of plus or minus about 2 to 3 degrees. We collected quite a few samples for different stations and then ran VOACAP. It was interesting that the model predicted the arrival angle within a few degrees for the actual angle observed with the highest number of occurrences. But it was very obvious that many angles were being used over a short period of time. I was invited back to the FCC HFDF site in Columbia after I retired from VOA. It seems that they built a home-brew design for a phased array which obtains full angle of arrival data in real time for any signal you want to look at... not only from Columbia MD but all of the 13 other remote FCC DF sites. Yes, takeoff and arrival angle predictions are WOEfully inadequate in VOACAP and all other models that I know of. I suspect that the minute-to-minute fading we observe in signal power is a direct result of ever changing angles. I think the effect is very large too... probably 8 to 16 dB. It was my suspicion that the great range in takeoff and arrival angles is why theory and measurement never agreed. What I saw with the real-time SkyLoc HFDF system is that in a few minutes, an entire envelope of arrival angles were measured. These arrival angles may be clustered around a single median or about several medians for multiple ray hop modes. What would be nice is to have enough worldwide data to develop the statistical window for the takeoff/arrival angles. The current FCC HFDF network might provide that data for a person interested in exploring this issue. When I was a Lt. in the Army, I was tutored in HF system design by Tim Shaw of the old Radio Propagation Agency. I was responsible for the design of the antennas being installed in SE Asia and Tim cautioned me not to use antennas whose beam widths were less than 10 degrees in either the vertical or horizontal plane. He cited cases where they had used antenna with beam widths as narrow as 5 degrees only to find that they experienced deep fading which he attributed to instantaneous variations in the arrival angle. Nearly 30 years later, I watched 57

in real time as the SkyLoc system recorded the distribution of arrival angles. How I wished Tim was still alive to see that! Time after time we would see plus or minus 4 to 8 degrees around the central angle per mode.

Minimum Angle in VOACAP Which Minimum Angle should we use for the antennas? 0.1 degrees or 3 degrees? Something else? George Lane: According to Donald Lucas, using 0.1 degrees gives you a better calculation of the frequency dependence of the ionosphere (i.e. the MUF for the lowest order mode for the circuit). John Lloyd told me the value of 3 degrees was better from a practical standpoint. It depends on the actual horizon clearance at both the transmit and receive site. If you are using a realistic radiation pattern taking into any horizon obstructions, then the low angles below 3 degrees will disappear anyhow. The reason for this is that gain at angles below 3 degrees for antennas over real ground is very low and also because John Lloyd programmed IONCAP (now VOACAP) to favor angles of 3 degrees or higher. So Lucas is right (use 0.1 degrees for minimum angle) when the radiation patterns for the antenna have very low gains at near-horizon angles. But if you don't know the low angle gain and/or are using isotropes, then Lloyd is right (use 3.0 degrees for minimum angle). If you see many cases where TANGLE is below 3 degrees, you should suspect you have used erroneous input somewhere. Is there something inherent to VOACAP to make the model always pick the lower takeoff and arrival angles? George Lane: The simple answer is: Yes, the model likes the lower angles because the path length is less and the transmission losses are less. The more complicated answer: Yes, VOACAP can miss the most reliable mode which is at a higher angle. How can this be? We have to that VOACAP only considers 3 modes for each ionospheric layer. So if VOACAP starts with 2F2 mode, then only the 3F2 mode and the 4F2 mode will be considered for the most reliable mode. But let's say that the antenna patterns have their maximum gain at higher angles, will the 5F2 mode be considered. No, it will not. What can we do to prevent VOACAP from finding the 'best' mode for the antennas we are using? The answer is fairly simple. If both the transmit and receive antenna have positive gain in dBi at angles below 3 degrees and there are no horizon obstructions, then one sets the minimum angle to 0.1 degrees in the input to VOACAP. If the transmit and receive antennas have patterns that combine to give maximum gain at angles above 3 degrees, then set the minimum angle to 3.0 degrees. Let's say I have a site which has an obstruction at the horizon of 9 degrees, should I use a minimum angle of 9 degrees? No! When you specify minimum angles above 3 degrees, you can make the program reduce the MUF. This causes the program to make all kinds of stupid predictions.Many people think that the minimum angle is used to for horizon obstructions and that is not true. The program lets you decide whether you can use angles of less than 3 degrees but should not be used to block higher angles above 3 degrees as that modifies the ionosphere. The best solution is to modify the antenna pattern for horizon obstructions using a program such as NEC.

3.4.3.1

Some examples

This is getting confusing I am sure. Let's take an example of a path from London to Raleigh NC. If I set the minimum angle at 0.1 degrees for antennas having maximum gain at angle well above 3 degrees, then I find that the most reliable mode is the 4F2 mode with takeoff and arrival angles of 15 degrees with a median SNR of 19 dB*Hz. The MUF is 16.4 MHz and the operating frequency is 7 MHz. One would suspect that this circuit should not be very reliable. But actual experience has shown that 7 MHz at 01 UT from EU to NC is very good. 58

So I set the minimum angle to 3.0 degrees in VOACAP. Now for these antennas with higher takeoff angles, I find the program selects the 5F2 mode at 21 degrees as the most reliable mode. Why did this happen? Before the program had found the 2F2 mode at 2.4 degrees as the lowest order mode. Then it applied the 3 hop rule and looked at the 3F2 and the 4F2 modes and stopped. When I used the 3 degree minimum angle, the 2F2 mode was blocked, so VOACAP started with the 3F2 mode at 9.4 degrees and then found the 4F2 mode at 15.2 degrees and the 5F2 mode at 20.7 degrees. The 5F2 mode has a median SNR of 23 dB*Hz. This is getting close to a SNR that can be used for reception of manual CW between trained operators. Also the MUF remained at 16.4 MHz for the 2F2 mode. I then set the minimum angle to 9.4 degrees to notch out the 3F2 mode. This caused VOACAP to reduce the MUF from 16 MHz to 13 MHz. That is not good as we have now modified the ionosphere with an obstruction angle. THAT IS A NO-NO!

Conclusion For most amateur applications, one should use a minimum angle of 3.0 degrees. The default value in VOACAP is 0.1 degrees. The reason for this is that the Voice of America spends a lot of money to build antennas that do produce considerable gain at angles below 3 degrees so we changed the IONCAP default from 3 degrees to 0.1 degrees for that reason. A note for VOA: If you use one of your variable beam arrays in the high angle mode, you should change the minimum angle from 0.1 to 3 degrees! A word of caution about isotropic patterns: Never use an isotrope with the minimum angle set to 0.1 degrees. The reason is that a gain of 0 dBi at 0.1 degrees is almost infinite gain from an antenna over a ground plane. VOACAP will lock on to that impossible gain and make predictions for modes that are really below the horizon. The program will ignore higher angle modes which are above the three hops which the program will consider.

Predicting the Takeoff Angle Parameter TANGLE Are both the TX and RX antennas considered while predicting the takeoff angle (TANGLE) of the transmit antenna? George Lane: For path lengths less than 7000 km, the angle prediction takes into the gain of both the TX and RX antennas. that VOACAP develops a reflectrix table of possible takeoff and arrival angles which will be ed on that path hour and operating frequency. The program finds the most reliable mode and its associated angle based on combining the path loss for the possible angles and the combined gain of the TX and RX antenna at each possible angle. For longer paths (over 7000 km) where the long-path calculation model (Method 21) can become the dominant propagation mechanism, the best takeoff angle and best arrival angle are computed and printed out based on the ionospheric conditions between 1000 and 2000 km of each end of the circuit. So, from a modelling point of view, is it better to use an isotropic RX antenna with +6 dBi gain, for instance, when we actually do not know all RX antennas, or should we just choose an antenna that could be perhaps most likely? George Lane: Good question. There are several factors. First we don't know what type of antenna is being used at the distant station. The directivity pattern is probably similar to a dipole but we do not know how well the antenna performs at the low angles nor do we know if the antenna is pointed at our location. It is the similar problem when you are dealing with ground-to-air HF communications. I have found engineers spend great sums of money to obtain accurate models of the aircraft antenna radiation pattern. But in practice, you don't know the orientation of the aircraft with respect to the ground station. So when in doubt about the distant station radiation pattern, the isotropic pattern is a reasonable first assumption. Any antenna placed over earth produces an average gain of 3 dBi (half of the power is radiated into the hemisphere and the other half is 59

reflected from the ground for a net gain of 3 dB over that of an isotrope in free space). Therefore, I would recommend u to a 3 dBi omni-directional pattern (isotrope +3 dBi). One must be careful with isotropes, however. Zero dBi or +3 dBi at 0.1 degrees elevation angle is a tremendous amount of gain compared to what is possible over real earth (-20 to -30 dBi is more realistic). With such gain at low angles, one will force VOACAP into erroneously predicting low angle modes with a very high signal power. To minimize the effect of this high gain at low angles, one should set the Minimum Angle at 3.0 degrees. Even a gain of 3 dBi at 3 degrees above the horizon requires a very good antenna. The second part of your question is whether or not there is a better antenna assumption for the distant station. If you are only dealing with a point-to-point circuit, one could assume, for example, a half wave dipole at 30 feet in height as a typical antenna. However, if you are using VOAAREA, one must specify a bearing angle for the receive antenna. With the assumed dipole, this bearing will be used at each grid point for the receive dipole. That means the radiation pattern of the assumed receive antenna will vary from one grid point to the next. One could use Inverse VOAAREA which would allow one to point the dipole at the grid points toward your receive location. But then again, one is faced with the problem of what bearing you should use for your antenna. I still prefer VOAAREA using an isotrope with up to 3 dB additional gain and a Minimum Angle set at 3.0 degrees for the general case when you don't know the details of the distant stations.

3.5 Conversions S DBW to S Meter Correlation Table The Z Tables

S DBW to S Meter Correlation Table The following table shows how S DBW (median signal power expected at the receiver input terminals) values can be mapped to S meter readings. There are a few assumptions: the receiver input impedance is 50 Ohms and the transmission lineloss is minimal. Also we assume that the S meter is correctly calibrated. In practice, S meters are mostly imprecise and can only give relative readings. S DBW W (50 Ohm) dBuV microvolts S Meter -43.01 5.00E-05 93.98 50000.000 S9+60 dB -53.01

5.00E-06

83.98

15811.388

S9+50 dB

-63.01

5.00E-07

73.98

5000.000

S9+40 dB

-73.01

5.00E-08

63.98

1581.139

S9+30 dB

-83.01

5.00E-09

53.98

500.000

S9+20 dB

-93.01

5.00E-10

43.98

158.114

S9+10 dB

-103.01

5.00E-11

33.98

50.000

S9

-109.03

1.25E-11

27.96

25.000

S8

-115.05

3.13E-12

21.94

12.500

S7

-121.07

7.81E-13

15.92

6.250

S6

-127.09

1.95E-13

9.90

3.125

S5

-133.11

4.88E-14

3.88

1.563

S4

-139.13

1.22E-14

-2.14

0.781

S3

-145.15

3.05E-15

-8.16

0.391

S2

-151.18

7.63E-16

-14.19 0.195

S1

60

The Z Tables 3.5.2.1

Converting Z values to Percentage Values and Corresponding Number of Days

Use the two tables below to convert the value of z to the probability (%) value and to the corresponding number of days. If you are using these tables...   

for converting a percentage value to days, just find the value. The corresponding number of days is in the right column. for calculating the REL, use Table 1 if the REQ.SNR is lower or equals to the predicted SNR. Use Table 2, if the REQ.SNR is greater than the predicted SNR. for calculating the MUFday, use Table 1 if the FREQ is equal to or below the predicted MUF. Use table 2 if the FREQ is above the predicted MUF.

Table 1. z 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 1.85 1.90 1.95 2.00 2.05

Table 2. %

50.00 51.99 53.98 55.96 57.93 59.87 61.79 63.68 65.54 67.36 69.15 70.88 72.57 74.22 75.80 77.34 78.81 80.23 81.59 82.89 84.13 85.31 86.43 87.49 88.49 89.44 90.32 91.15 91.92 92.65 93.32 93.94 94.52 95.05 95.54 95.99 96.41 96.78 97.13 97.44 97.72 97.98

Days/month 15.00 15.60 16.19 16.79 17.38 17.96 18.54 19.10 19.66 20.21 20.74 21.27 21.77 22.26 22.74 23.20 23.64 24.07 24.48 24.87 25.24 25.59 25.93 26.25 26.55 26.83 27.10 27.34 27.58 27.79 28.00 28.18 28.36 28.52 28.66 28.80 28.92 29.04 29.14 29.23 29.32 29.39

z 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 1.85 1.90 1.95 2.00 2.05

%

Days/month

48.01 46.02 44.04 42.07 40.13 38.21 36.32 34.46 32.64 30.85 29.12 27.43 25.78 24.20 22.66 21.19 19.77 18.41 17.11 15.87 14.69 13.57 12.51 11.51 10.56 9.68 8.85 8.08 7.35 6.68 6.06 5.48 4.95 4.46 4.01 3.59 3.22 2.87 2.56 2.28 2.02

14.40 13.81 13.21 12.62 12.04 11.46 10.90 10.34 9.79 9.26 8.73 8.23 7.74 7.26 6.80 6.36 5.93 5.52 5.13 4.76 4.41 4.07 3.75 3.45 3.17 2.90 2.66 2.42 2.21 2.00 1.82 1.64 1.48 1.34 1.20 1.08 0.96 0.86 0.77 0.68 0.61

61

2.10 2.15 2.20 2.25 2.30 2.35 2.40 2.45 2.50 2.55 2.60 2.65 2.70 2.75 2.80 2.85 2.90 2.95 3.00 3.05 3.10 3.15 3.20 3.25 3.30 3.35 3.40

98.21 98.42 98.61 98.78 98.93 99.06 99.18 99.29 99.38 99.46 99.53 99.60 99.65 99.70 99.74 99.78 99.81 99.84 99.87 99.89 99.90 99.92 99.93 99.94 99.95 99.96 99.97

29.46 29.53 29.58 29.63 29.68 29.72 29.75 29.79 29.81 29.84 29.86 29.88 29.90 29.91 29.92 29.93 29.94 29.95 29.96 29.97 29.97 29.98 29.98 29.98 29.99 29.99 29.99

2.10 2.15 2.20 2.25 2.30 2.35 2.40 2.45 2.50 2.55 2.60 2.65 2.70 2.75 2.80 2.85 2.90 2.95 3.00 3.05 3.10 3.15 3.20 3.25 3.30 3.35 3.40

1.79 1.58 1.39 1.22 1.07 0.94 0.82 0.71 0.62 0.54 0.47 0.40 0.35 0.30 0.26 0.22 0.19 0.16 0.13 0.11 0.10 0.08 0.07 0.06 0.05 0.04 0.03

0.54 0.47 0.42 0.37 0.32 0.28 0.25 0.21 0.19 0.16 0.14 0.12 0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.03 0.02 0.02 0.02 0.01 0.01 0.01

4. VOACAP - Case Studies VOACAP Case: Make your beacon predictions VOAAREA Case: RUV Gufunes

VOACAP Case: Make your beacon predictions The NCDXF (Northern California DX Foundation), in cooperation with the IARU, has constructed and operates a worldwide network of high-frequency radio beacons on 14.100, 18.110, 21.150, 24.930, and 28.200 MHz. These beacons help both amateur and commercial high-frequency radio s assess the current condition of the ionosphere. These automatic beacon stations transmit every three minutes on the given frequency, 24 hours a day. A transmission consists of the callsign sent in Morse code at 22 words per minute followed by four one-second dashes. The callsign and the first dash are sent at 100 watts. The remaining dashes are sent at 10 watts, 1 watt and 0.1 watts. The current NCDXF beacon list is as follows:

1 2 3 4 5 6 7 8 9

DX Entity

Call

Location

Lat

United Nations Canada United States Hawaii New Zealand Australia Japan Russia Hong Kong

4U1UN VE8AT W6WX KH6WO ZL6B VK6RBP JA2IGY RR9O VR2B

New York City Eureka, Nunavut Mt. Umunhum Laie Masterton Rolystone Mt. Asama Novosibirsk Hong Kong

40 79 37 21 41 32 34 54 22

62

45 59 09 38 03 06 27 59 16

Lon N N N N S S N N N

73 85 121 157 175 116 136 82 114

58 57 54 55 36 03 47 54 09

W W W W E E E E E

10 11 12 13 14 15 16 17 18

Sri Lanka South Africa Kenya Israel Finland Madeira Argentina Peru Venezuela

4S7B ZS6DN 5Z4B 4X6TU OH2B CS3B LU4AA OA4B YV5B

Colombo Pretoria Kiambu Tel Aviv Karkkila Santo da Serra Buenos Aires Lima Caracas

6 25 1 32 60 32 34 12 10

54 54 01 03 32 43 37 04 25

N S S N N N S S N

79 28 37 34 24 16 58 76 66

52 16 03 46 06 48 21 57 51

E E E E E W W W W

Each station consists of a 100W transceiver and a vertical antenna.

3.5.3.1

Setting VOACAP input values

Just follow the nine easy steps below to set up your VOACAP correctly (we suppose you have made the default VOACAP installation at C:\itshfbc):    

  

 

ncdxf.zip (containing all input data preset). Unzip ncdxf.zip (unzipped: ncdxf.voa) to the C:\itshfbc\saved\default\ directory. Create a directory called "" under the C:\itshfbc\antennas directory. Unzip the following files to the C:\itshfbc\antennas\ directory:rxgp.zip (unzipped: rxgp.ant) and txgp.zip (unzipped: txgp.ant). These antenna files contain the typical pattern for a vertical antenna and will be used in the calculations. The files are courtesy of Fabio Bonucci, IK0IXI. Launch VOACAP. Open ncdxf.voa from the File menu (File > Open). Set the appropriate month and SSN (Smoothed Sunspot Number) to "Groups". The current SSN numbers can be ed fromNational Geophysical Data Center (Predicted Monthly Sunspot Numbers). Set the "Transmitter" location by choosing the location from a list that comes with the VOACAP package (ncdxf.geo), or by entering the transmitter location and coordinates manually. Set the "Receiver" location, e.g. the coordinates of your location.

3.5.3.2  

Running the predictions

Run the graphical prediction by choosing Graph from the Run menu (Run > Graph). When the calculations are done, you will be prompted to choose the output parameter you are interested in. Choose REL (Time availability, % time SNR exceeds required SNR).

The different colours will indicate the reliability (%) to achieve the required SNR for communication. The best reliability is shown in white and the worst in dark gray. Look at the colour legend for values. Now when you are all set, try running the circuit analyses from various NCDXF beacon locations to your receive location, and you will get a glimpse of best times for openings to all corners of the world.

VOAAREA Case: RUV Gufunes This is a case study that tries to guestimate the coverage area of Icelandic National Broadcasting Service (RUV), based on information provided in Radio Nederland's recent article on the station. It also serves as a practical example of how to use VOAAREA even if some of the critical input parameters are missing; in RUV's case, the exact transmitting antenna setup.

3.5.4.1

Collect all necessary input data

63

Start by reading the RNW (Radio Nederland) article on RUV,http://www.rnw.nl/realradio/features/html/iceland020111.html. Look for the following data:     

transmitter coordinates transmitter power times & frequencies of transmission transmitter antenna antenna beams

3.5.4.2       





 





Enter the input parameters

Launch VOAAREA. Set Parameters to REL (Circuit reliability). It predicts us the percentage of the days in the month that the REQ.SNR will be met. Set Path to Short (Path). Set Coefficients to CCIR (Oslo). Set Method to 20 (Auto Select). Enter the transmitter coordinates: Latitude 64N05, Longitude 21W51, Name GUFUNES. Enter Plot Center. Click "Set to transmitter". Then select appropriate X-range and Y-range values. Test your map by viewing the map only (Run > Map only) until you are happy with it. Our values were: Xmin -2000, Xmax 4500, Ymin -3000 and Ymax 2500. Enter Groups values. The first Europe transmission takes place at 1215-1300 UT on 13865 kHz so enter 13 as the time and 13.865 as the frequency. The second transmission takes place at 1755-1825 UT on 11402 kHz. Enter 18 UT and 11.402. The month is January (1) and the SSN (the monthly smoothed sunspot number) is estimated to be 110. Enter System values. Man-made Noise 145, minimum take-off angle 3 degrees, required reliability 90%, required SNR 67 dB-Hz (a value representing a reasonable grade of service), multipath power tolerance 3 dB, max time delay 0.1 ms. Ensure the Fprob values are 1.0 / 1.0 / 1.0 / 0.0. Set the transmitter antenna (Tx antenna). This is the trickiest part. Launch the HFANT program. Open the Sample.07 file (a sample Rhombic antenna) from the Samples directory. Set the height above ground to 27 meters (as discussed in the article). Run Plot patterns > Vertical to see the take-off angle. Set the frequency to 13.865 (MHz). The best angle is at 8 degrees and the directivity gain is quite high. Still, let us try with this one. Save the new antenna model under a different name. Enter the new name by pressing "File name" button. Then click "<<Save as.." button to really save it. Now press the "Tx Antenna" button on the VOAAREA main screen. Press "Transmitter Antenna" button to select your newly-saved antenna. Set the design frequency to zero. Set the main beam to 125 degrees, and the power to 70% of 10 kW, ie. 7 kW. This is because we assume some line losses. Rx antenna. Accept the default SWWHIP.VOA antenna.

As a result, the VOAAREA main input screen should look like this:

64

3.5.4.3     

Run the prediction

Choose Run > Calculate > Save{temp.VOA}/Calculate. To plot the map after calculations, choose Run > Plot results. Open the first file to be plotted: File > open TEMP.VG1. If you do not wish to change the default colours or values, just choose Plot to > Window. To view the 18 UT map, first Exit the current map, and choose File > Open > temp.vg2.

Voila! This is approximately what you should see (I have changed some of the default colours for my maps): 13 UT - 13865 kHz

18 UT - 11402 kHz

65

Legend