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There are three parts to my amateur weather satellite station, an antenna to pick up the signals, a receiver, and a PC with a sound card.
I also have a Turnstile antenna mounted outside - and comparing results between the loft-mounted QFH and the outdoor Turnstile, I find that the outdoor antenna wins. I also have an outdoor QFH, but find its better response near the horizon also produces greater interference from pagers necessitating an external filter.... Turnstile antenna links - please let me know of more!The turnstile has a poorer response near the horizon, which doesn't help if you are trying to get the maximum range i.e. near horizon passes, but which may help if you are getting interference from pager transmissions, for example.
QFH antenna links - some still work...
Other antenna linksTo convert the 137MHz FM signals into audio, you can use a scanner, such as the Icom IC-R2, but as the FM deviation of the signal is 17KHz and scanners expect 5KHz, white parts of the signal will be lost or distorted. It's a good way to start, though, if you already have a scanner. Having tasted what was on offer, I bought a more specialised receiver. This receiver scans the satellite channels and beeps when a signal is available. Specially modified scanners are available from the Hoggwild site in the USA, and I can recommend the R2FX and R2ZX receivers available from the GEO Shop.
Between the antenna and the RX2, you can add a pre-amp, which will boost weak signals when the satellite is near the horizon however if, like me, you live in a good VHF location (on a hill or near other transmitters) you may find that a pre-amp simply exacerbates interference from other signals. In the UK we have pagers sharing the same frequencies as satellites (no, I don't understand why, either) so interference from strong transmissions on adjacent frequencies is a real problem. I found that the audio level from the RX2 was higher than that from the scanner, so I attenuated it before feeding to the sound card of the PC, you may not need to do this. On the PC, free private use software is now available called WXSat from Christian H. Bock that will do a software demodulation of the AM subcarrier that comes from the receiver. (The original video signal from the satellite is first used to amplitude modulate a 2400Hz carrier, which then frequency modulates the 137MHz downlink signal). Les Hamilton has some useful Beginner's Notes on WXSat. This software can compensate for sampling rate errors in your sound card, and it is well worth taking some time to set up the software correctly. This involves editing a data file with results from dialog boxes but is quite straight forward. A great feature of this software is the automatic recording mode - if you have a reasonable signal and not just a piece of wire as the aerial - you can leave your PC on and any satellite signals that appear from your RX2 can be saved to disk as wave files, pictures or both. I subsequently ended up writing my own software called SatSignal for off-line decoding of signals with accurate temperature information, and I used Max Hadley's modifications for serial remote control of the RX2, again with my own control software, thus automating weather satellite reception. You might also want to know when satellites are about to appear over your horizon - the program I started with was C. D. Gregory's WinOrbit. I found that as supplied, the program ignores drag terms, which make a substantial difference to the results, so be sure to enable drag terms and use the most accurate orbital model your processor can handle. The Space-Track Web site is an excellent source of up-to-date orbital parameters. Again I have ended up writing my own software for orbit prediction, WXtrack, which allows overlay of a predicted and actual satellite image, thus helping you to judge where you are seeing when the clouds predominate! You can see a small set of results on this Web site. |
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