VOACAP Quick Guide

HF Propagation Prediction and Ionospheric Communications Analysis
by Jari Perkiömäki, OH6BG/OG6G

What is VOACAP?

VOACAP (Voice of America Coverage Analysis Program) is free professional high-frequency (HF) propagation prediction software from NTIA/ITS, originally developed for Voice of America (VOA).

This 'work-in-progress' guide should get you well started with the software. A more comprehensive discussion about the finer details of using the software can be found in George Lane's book Signal-to-Noise Predictions Using VOACAP. A User's Guide. The book is now available on CD-ROM.

There is now also "The Official VOACAP Blog" - well, it's not too official.

NOTE: Running automated scripts to access VOACAP services is prohibited unless agreed upon in advance with the VOACAP site owners.


I am happy to announce that VOACAP Online has now an option to offer do-it-yourself HF propagation predictions, suitable for the websites of DXpeditions (and for other needs, too). Just embed a simple snippet of code in your HTML codebase, and you are set to go. It's free. Read more at: http://www.voacap.com/diy-charts.html


A key VOACAP input parameter is the Sun Spot Number (SSN). The National Geophysical Data Center (NGDC) / National Oceanic and Atmospheric Administration (NOAA) has, at the end of 2016, discontinued providing this invaluable predicted data, instead directing users to the SIDC website.

Jim Watson, one of the key figures behind VOACAP Online and a maintainer of his own Proppy website, has conducted a survey, comparing the effects of three SSN data sets: Original NOAA values, SIDC values, and adjusted SIDC values. The results indicate that VOACAP performs best with the original NOAA SSN values. Now, going forward, we will need to use 'adjusted' SIDC SSN values as a substitute.

Read Jim's blog post or the full version (as PDF).

VOACAP Online Prediction Services

Point-to-Point Predictions

11M Point-to-Point Predictions

  Coverage Area Maps

11M Coverage Area Maps

VOACAP Propagation Planner
Visual tool for HF contesters and DXers
  VOACAP DX charts
Predictions for upcoming DXpeditions

Other VOACAP Related Services

VOACAP Greyline

What's New?

1. Downloading VOACAP

2. VOACAP - Backgrounds & Running the Prediction


The calculation engine, VOACAPW

Graphs & Colours

3. VOACAP - Understanding the Prediction



Signal Power & Noise Power

Antennas & Radiation Angles


4. VOACAP - Case Studies

5. VOACAP-related Papers

6. NTIA/ITS HF software HELP Topics

7. HamCAP User's Guide

8. Articles of interest





9. Tools & downloadable files for use with VOACAP

Find coordinates and Maidenhead grid locators just by pointing and clicking



Coordinate files

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

Antenna and configuration files

Special Thanks
I wish to thank Mr George Lane for his friendship, invaluable comments and guidance - and his patience in this project. A special thank-you to Greg Hand who still maintains the code.

Disclaimer: Any software or service on this website is provided "as is". Use at your own risk.

© 2003-2018 Jari Perkiömäki OH6BG/OG6G. SSN source for all VOACAP Online services: WDC-SILSO, Royal Observatory of Belgium, Brussels. Last update: 19 May 2018.