Hi guys,
Rod asks:
Also decoding telemetry from the birds, is there a "one size fits all" software or does each satellite have specialized software for doing this?
There is no one single program that does everything for every amateur radio satellite.
However, you can do much of the work completely in software. For example, when AO-40 was still active it was common to receive the 400 bps telemetry signal with your radio, then demodulate the signal with a soundcard and AO40Rcv (software) and then display the telemetry with P3T, another piece of software. These days you can accomplish a similar feat for currently active satellites like AO-51, albeit using totally different software packages.
If you're really interested in digital satellite modes you might want to check out the AMSAT Digital CDROM - it comes with several digital program and test signals for everything from 1200 baud to 38k4 baud. (Disclaimer: I had a hand in the making of a couple of the items on the CDROM.)
[email protected] wrote:
Apparently nobody has yet written software that can demodulate 38600 bps (or 38k6).
Actually, it's 38,400 bps (38k4) and, yes, there is software that will demodulate the signal using only a soundcard. I know because I wrote it. :-) For my version, see the paper "A First Look at a New Soundcard DSP Modem for Satellite Telemetry" in the 2005 AMSAT Symposium Proceedings, or just email me with your questions.
The 38,400 bps signal will just fit into the bandwidth of a soundcard running at 48,000 samples per second. (No, this doesn't violate Nyquist.)
And I'm not the only one to write software for 38k4. There's also a 38k4 DSP modem for the DSP56002EVM, if you have one of those. (I don't.) See
http://bips.bi.ehu.es/prj/modem/tossa/index.html
for their 38k4 software modem that runs on a DSP56002EVM. There's probably others too.
The tricky part, in my opinion, is receiving the 38k4 signal and getting it (undistorted) into the soundcard. At RF you need a very wide filter to pass the whole FM signal, and as an audio signal, its spectrum goes from almost zero Hertz up to 19,200 Hertz. Some FM receiver chips, which would work fine at 9600 baud, have a frequency response that cuts off before 19,200 Hertz. With the effects from the RF filter, and the FM receiver chip combined, in some receivers the 38k4 signal will never make it to the soundcard. But I digress...
Anybody know a good drop in replacement for something like an MC13135P that would work up past 20,000 Hertz?
Douglas KA2UPW/5