Satellite tracking: High tech and low budget
Everybody who enjoys the view of the night sky has seen them: more or less bright spots moving with constant speed and direction across the field of view – satellites. Both the technical challenge and the experience to connect with something high up in space make receiving and decoding radio signals from satellites an interesting experience.
My own interest in this subject started when I saw the International Space Station at night and I was able to listen in on the ISS's amateur radio frequencies with my hand-held radio scanner at the same time.
I found it even more fascinating that you do not need expensive radio equipment to start with satellite tracking. Thanks to ‘Software Defined Radio’ (SDR) technology, a computer and a simple USB dongle that costs around £15 can get you going.
The basic idea behind SDR is to replace the usual components of a radio, like filters and demodulators, with a piece of software that does their job. The only hardware that is needed is an analog-to-digital converter that converts the radio signal that comes from the antenna into a stream of bits and bytes that the computer can process.
The good news is that this is nothing special: some radio amateurs discovered that a range of cheap USB dongles that you can buy to watch digital television with your computer work exactly in this way.
It is important that the dongle contains the RTL2832U chip, sometimes called RTL-SDR. You will find plenty of offers on the internet and there is even a dedicated website www.rtl-sdr.com with plenty of information and links to software for all operating systems.
I was able to receive the ISS with a simple telescopic aerial. Directional antennas give much better results, but have to be pointed into the direction of the satellite, which requires constant tracking either by hand or an antenna rotor.
Again no big budget is required: I built a simple Yagi antenna for the 2-metre band out of the elements of an old Venetian blind and it did a fairly good job. It is advisable to place the antenna a few metres away from your laptop, because the computer itself emits a lot of radio noise that can interfere with the signal.
Most amateur radio satellites operate in low earth orbits and use the 2-metre (144-146Mhz) and 70-centimetre (430-440Mhz) bands. This means that the satellite can only be received for a few minutes, when the satellite is above the horizon and ‘visible’ for the receiver.
There are both websites and software that can help with getting information about satellite passes in your location. The site www.satview.org is a good starting-point, and amsat-uk.org provides plenty of information about almost everything around amateur radio satellites
Enjoy pointing your antennas to the sky!
Mark Dammer
