Propagation Forecasting Tools 1: VOACAP

Rainbow Trout, North Carolina, May 2014
Some days everything works right! North Carolina, May 2014

One of the things that fascinates me most about amateur radio is the vagaries of ionospheric propagation. It’s a lot like fly fishing (another of my hobbies): some days you get a lot of action with just about any fly. Other days, you have to be very selective about your fly choice and the depth at which you fish it, and you still may get nothing. Heading to the radio shack is a lot like stepping into a stream. I may find the bands wide open, and land several DX stations in the first 20 minutes, or I may have to search around on the bands to find what’s working. Fortunately, there are a few tools out there to help me figure out where to start.

The one I find the most useful is the Voice of America Coverage Analysis Program, or VOACAP. I like this tool because it is based on mathematical models and ionospheric observations. Some of the other tools that I’ll discuss in future posts, like the Reverse Beacon Network or WSPRNet are also useful, but you only get data from a given location if there’s an operator there participating in those efforts.

Coverage Area Maps

VOACAP has several tools available, and each is useful, depending on what you want to know. I usually start with a coverage area map, to get an idea of where my signals will likely be heard. If I’m working CW, for example, since I am not so confident yet in my ability to copy DX call signs, I usually look for a band that will cover a lot of the US, but not much outside. If I want to work SSB or digital, and am looking for an ATNO, I will instead look for as wide a coverage area as possible, and will not be as concerned about a large skip distance around my QTH. The coverage map gives a form to enter your station details. If you enter your 6 digit grid square in the Name box, and click the Loc Calc button, it will automatically enter the latitude and longitude. Then you can select other relevant parameters. For example, the coverage for my station running 100 watts on 30m CW is shown below.

30m CW propagation forecast, with 100 watts TX power
30m CW propagation forecast, with 100 watts TX power


Point-To-Point Predictions

Another useful tool from VOACAP is the point-to-point prediction. With this tool, you enter your station details as before, but this time you also enter details for a specific receive site. This is useful if you want to make contact with a specific location. The results give you an idea of the best band to use at a particular time of day. For example, if I wanted to reach friends in northern England, the diagram below shows that my best chance will be on 40 m early in the morning or 20 or 17 m later in the day (UTC time). Even then the odds will about 50/50 of making the contact.

Point-to-point prediction from my QTH to northern England
Point-to-point prediction from my QTH to northern England

Propagation Planner

The last item I’ll mention is the propagation planner tool. These results give an broad overview of expected conditions on all bands to other parts of the world. This is useful if you don’t have specific goals at the time, but want to know what to expect. You can display the data in a couple of different ways: for each CQ zone, in which you get a series of charts, one for each geographic region, that displays frequency band vs. time, or by band, in which case you are shown a chart that shows reliability of the selected band by time to each geographic region. These plots are fairly large, so I’ll leave it to you to experiment and look at the results for yourself.

There is another tool similar to the propagation planner, but for any specific DXpedition stations that may be on the air at the time. This will allow you to plan your attempts to break through the pileups with the best probablility of success.

So that’s all for VOACAP. Next time I’ll post about the Reverse Beacon Network and other similar propagation reporting sites.



Scott WZØW

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