Poor Man’s Guide to WSPR Spots
Okay, so I’ve been playing around with generating various kinds of visual signals on the MEPT subband on 30m. That’s the 100hz wide band just above 10.140Mhz, and it’s fun, because there are a number of “grabbers” which have the spectrum displays from their radio receivers available on the web. But there is a minor problem: there aren’t that many of them here in the U.S., and propagation often makes it difficult to find them.
But there is an alternative: WSPR. WSPR is a beaconing mode designed by K1JT, Joe Taylor, a Nobel Prize winning Princeton physicist. He is also the author of the program WSJT, which is used by many EME and weak signal operators to allow them to exchange messages at very low signal levels. WSPR encodes a callsign, grid and power level as a 162 symbol long sequence of FSK tones 1.46 hz apart, lasting for about 110 seconds. Joe’s code is open source, which is awfully cool, but a lot of it is written in FORTRAN and I’ve had difficulty getting it to run on my Macintosh. It’s probably that I’ve got a slightly odd development environment, but it’s been frustrating.
And here’s the other thing: I really don’t need all the heavy lifting to process receive level stuff. Ultimately, I’d like to be able to send this stuff with just a little microcontroller, with a fixed message. That isn’t hard, but it’s hard to get the exact details of the protocol description without digging into the source code.
But I did finally figure out how to generate a compatible message. It turns out that you can get a Windows command-line program from Joe’s website, called WSPR.EXE. If you read really carefully, you will realize that it can be tricked into telling you which tone it sends in each of the 162 slots for a messag that you specify. I specified a message containing my call (KF6KYI) my grid (CM87) and my power (27dBm or 0.5 watt), and it dumped the tones. From then on, all the work I’ve been doing with writing CW and Feld Hell encoders helped, and I generated a little WAV file that had the right tones in it. I imported that into iTunes, and then played it into my FT-817 at the beginning of an even numbered minute. I then went to the automated WSPR logging site, and…
I think another hour’s worth of work, and I could have the entire thing automated, and it would totally work. Very neat.