Professional HF Propagation Prediction Code: VOACAP
In the opinion of many, VOACAP (Voice of America Coverage Analysis Program) is simply the best choice around when having to select a HF propagation prediction code. It simply takes so many more factors into account such as the required signal to noise (S/N) factor and the properties of the transmitter and receiver antennas.
The good news is that you can download this marvelous piece of software for free! But before you head off, it is a good idea to read this excellent Propagation Theory and Software primer by Jim Coleman, KA6A. It explains very well how to use VOACAP and for those who have not made up their mind yet, many screenshots of VOACAP are shown.
Part I - Introduction
Part II - VOACAP (IONCAP)
Part III - CAPMAN
Part IV - Contest Planning
Jari Perkiömäki, OH6BG, even made a true VOACAP resource centre available on the web. Check out his VOACAP Quick Guide.
You still need to convincing? Then read also what antenna-modelling guru Brian Beezley, K6STI has to say about VOACAP. Brian is the author of the MININEC and Antenna Optimizer (AO) antenna-modelling software.
Here is the VOACAP software:
Download HFWIN32
(Contains amongst other similar programs, a 32-bit version of VOACAP for Windows-NT/2000/XP/Vista & 95/98/ME.)
Be careful: Unlike above applet, this program requires the current Smoothed Sunspot Number (SSN) as input, not the Solar Flux (SF). The current SSN can be obtained from this page.
Most useful are the Signal-to-Noise Ratio (SNR) area plots. Make sure you understand and apply the fundamental relationship between signal bandwidth and required SNR normalised at 1Hz bandwidth. The latter is greater than the required SNR at signal bandwidth. Alternatively, simply use the RECAREA program instead (also included with this download). In this program you can specify signal bandwidth directly.
Bandwidth, bit rate and SNR at bandwidth are, in turn, related by Shannon's Theorem.
Finally, the gain of sample antennas can be reviewed using the included HFant program. If necessary, modify the antennas or import antenna patterns from the 4nec2 antenna modelling software.
VOACAP User-Interfaces for Amateur Radio Use
As stated in its name, VOACAP was originally designed for analysing the geographical coverage of the Voice of America broadcast station. Now, broadcast stations typically have fixed antenna arrays beaming in a fixed direction. Many amateur radio stations, on the other hand, have rotateble directional antenna systems. VOACAP is cumbersome in dealing with rotable antenna systems. You would need to run an analysis for every antenna bearing. Luckily, there are a few great VOACAP user-interfaces that get around this problem in a very elegant way.
VOAProp
Julian Moss, G4ILO, programmed an excellent easy-to-use VOACAP user-interface. My only criticism is that it lacks the real signal-to-noise analysis of VOACAP and that everything is all a bit relative (no properly defined antenna, power nor bandwidth settings). Nonetheless, it shows you in real-time what is possible in terms of propagation and it might be your entry-ticket to start using VOACAP. Visit G4ILO's Shack and download VOAProp for free!
HamCAP with DX Atlas
Written and distributed for free by Alex Shovkoplyas, VE3NEA, HamCAP combines the full power of real-time DX-spotting and VOACAP HF propagation predictions with DX Atlas, an excellent topographic DXCC atlas. It is the «Nec Plus Ultra» (Latin for "Nothing goes beyond") of HF propagation software and is top-of-the-list in Thierry Lombry, ON4SKY's comparison of 13 shortwave propagation programs for amateur radio use. Read ON4SKY's detailed review, to understand why. Here at ON4AA, I even installed a second video card and computer monitor to have DX Atlas on display at all times when I am in my shack, much like famous low-band DXer John Devoldere, ON4UN, does (see below).
Picture: John, ON4UN, displaying DX Atlas on his middle computer screen