Voice of America Coverage Analysis Program VOACAP


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).

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.

The VOACAP evolution chart (courtesy of George Lane, Lane Consultant).

Main features

  • 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 user interface and, for advanced users, powerful command line options
  • Detailed Point-to-Point graphs and Area Coverage maps for 22 parameters of circuit quality such as
    • SNR (Signal-to-Noise Ratio)
    • Reliability
    • Required Power Gain
    • Signal Power
    • MUF
    • 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 user assigned frequencies, such as
    • Point-to-Point Performance vs Distance at the given hour for the given parameter at one or all user assigned frequencies
    • Point-to-Point Performance vs Time for the given parameter at one or all user assigned frequencies on the 24-hour scale
  • User defined circuit databases for repeated or batch calculations
  • Thirty calculation Methods for
    • ionograms
    • antenna patterns
    • 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
  • Accepts unlimited number of user defined location databases
  • Database of hundreds of transmit and receive antennas, with ability to user adjustments using HFANT, for
    • amateur radio
    • broadcasting
    • SWL, and more
  • Accepts unlimited number of user defined antenna files (HFANT and Type 11 & 13)
  • Comprehensive, user-community supported online VOACAP services available for beginners and advanced users
  • FORTRAN source code freely available for the prediction module of VOACAP [VOACAPW]
  • Not subject to copyright protection in the U.S.
  • VOACAP for Windows available for free downloading from the U.S. Department of Commerce (NTIA/Institute for Telecommunication Sciences; Boulder, Colorado).

VOACAP screenshots

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 user 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.

The Input Screen

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

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.

User-defined Frequencies vs. Time Graphs

This is the 24-hour analysis graph of the given output parameter on user-defined frequencies from the UN to Cape Verde, Africa. The user 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 user can easily understand the behaviour of the lower frequencies and higher frequencies at the different times of the day on the given circuit.

User-defined Frequencies vs. Distance Graphs

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

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 user. 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 (May, SSN 50) at 12 UTC. A total of 23 output parameters can be plotted on the map.