During some discussions with AA7EE regarding a seeming lack of 20 meter propagation between us at any time right now, we both decided to do a bit of research into what was even feasible according to predictive software. Dave went to the VOACAP web service from OH6BG to get some nice plots which showed that indeed it would be nearly impossible for us to make a 20 meter QSO right now.
The web site is nice, but being a Linux nerd, I wanted to see if I could find comparable software for my PC. A small bit of searching led me to VOACAPL from HZ1JW, and the matching package pythonProp, which gives a GUI frontend to the CLI VOACAP interface.
The installation of the VOACAPL software is quite easy if you are using Ubuntu. Just download the .DEB file and install using your favorite package manager. Installing pythonProp is a bit more involved, since there are a fair number of dependencies to install first, but as long as you closely follow the instructions on the website it shouldn't be much of a problem.
If you are like me and the thought of tackling VOACAP through the command line was a little bit daunting, then the voacapgui tool (in the pythonProp package) is just what you are looking for. The GUI has three main tabs for interacting with the program: one for the site information (transmitter and receiver QTH, antenna, and power), one tab to execute point-to-point channel analysis, and one for generating area propagation maps.
As you can see above, the P2P tab can get you a nice plot of the probability of making a QSO over a certain path with the specified antennae and power levels. And since this is a Linux port of the program that Dave used on the web, the data we got back was nearly identical. No 20 meter QSOs for us right now.
Here you can see an area map showing circuit reliability for 7 MHz at 0300 UTC during Oct 2011 using 5 watts. That doesn't look very good! (Sometimes I wonder if the predictions for low power are a bit out-of-whack. This software was originally written for VOA, so I wonder if it's really calculating the reliability for a 5 W AM signal. I am a total novice at this, so I expect some VOACAP expert will probably put me some knowledge on this, as the kids say).
Any way, it's a neat package to play around with if you have a Linux box. Many thanks to HZ1JW for taking the time to port VOACAP over to Linux in a easy-to-use package.
Sure enough, I made a mistake. Had I read the documentation more thoroughly, I would have seen that parameter Required SNR was set to a default suitable for SSB. At least I was onto the right idea a few paragraphs above. Here's the same area plot as before, but with the Required SNR set for a suggested value of 24 for CW operation.