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Weather Satellites

Posted 04-02-2009 at 10:29 AM by uinseann

A few years ago now, I bought a Bearcat hand held scanner for listening to radio hams etc. While scanning in the 135mhz band, I came across a noise rather like a clock ticking and a faint bell sound.I couldn't work out what it was so I bought a book with all the frequencies in. It turned out I was hearing NOAA sun synchronous Weather satellites.

I only ever heard these signals rarely, just by chance, because they had to be very close before you could pick them up, and at the time there were only about 3 operational, and they alternate them. I am a curious person and had to know more about this subject. Thanks to the power of the internet everything was there for me. First things first I needed to know more about the Satellites. There were (at that time) Satellites from USA, Russia, and China.

I used that other operating system at that time, and I found a few programs to help me calculate when these Satellites would be in range. This software had to be updated every few days, with "Keplarian Elements." Keplarian Elements are just (well not just) a mathmatical way (number crunching), of predicting the position of any satellite's position in space, by using data from when they were launched, rate of decay,where you are,etc. If you can get Elements for the shuttle you can even find out when and where it is, and sometimes go star gazing, hoping to see it! Some clever people can do all this with pen and paper (I don't fit into that category). The problem was although I dabbled with Linux I'm afraid there were very few programs to do the number crunching, and the few that were available had to be compiled from source. So; I used freeware for that other operating system!

I could go on all day about this subject but I would bore everyone! But; so you get the gist of it, I had software to predict the Satellite passes in table form, and/or a nice map with Satellites moving about. I then had software which controlled my sound card. The idea is you plug the scanner into the 16 bit sound card by a normal cable from the headphones jack into the "line in" of the sound card.Some software just recorded the signal and then this had to be run in another program which by magic built up a picture in black and white and line by line of what your location looks like from above, on your monitor. I also found software to record and decode combined, as time went on, and then the ultimate; wxtoimg (wx to image), this software predicted recorded decoded all together. It could also be done by timer. Of course it's not that simple because I needed a better antenna than the rubber duck that came with the scanner. I researched and in the end, again by the power of the internet, built one and stuck it in the loft. Although I built it, and the scanner bandwidth was too narrow I got some excellent pictures.

All in Linux! The software wxtoimg is still available for download (although sun synchronous satellites are few now thanks to geostationary satellites, which needs more expensive hardware).There are packages for that other operating system, deb, rpm and tgz.
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