One of the things that has been a “bee in my bonnet” was successfully making a contact via an amateur radio satellite. Years ago, at a Field Day event, I attempted too make such a contact. I had the Arrow antenna mounted on a tripod, used Orbitron to determine the flyover opportunities, and had my Yaesu handheld at the ready to listen in.
It was a total flop. Not a single bit of received audio crackled over the handheld. Manually scanning the path with the Arrow antenna, I was hunting and pecking – nothing. Others at the club attempted, they got what sounded like audio received by the satellite, but no solid audio reception.
So I decided what was needed as a slow approach to this. What I needed to do was build up my experience with receiving satellite signals first, and do it with a fixed antenna. From there, once I had a way of detecting satellites reliably, I could then focus on how to lock onto a satellite with a directional antenna. I decided a good way to start, would be to learn to do weather satellite reception, using an SDR and making use of SDR software waterfall to visually detect satellites once they crossed the AOS point stated by prediction software.
Luckily, the good folks at www.rtl-sdr.com has some nice tutorials on how to receive weather images from NOAA satellites. (link here)
The system consisted of having an appropriate antenna, a capable SDR dongle, SDR software, and the software WXtoImg to do the satellite overpass prediction and process the received audio to a weather image. What really pressed me into action was one cold December night, I was using my Yaesu VR-500 scanner, and I was scanning the airband, and I kept going beyond the airband, and I noticed what sounded like a repeating data signal. Realizing I was past the airband, I checked what other transmissions could be in that frequency range. Once I saw that NOAA satellites transmitted at 137 MHz and higher, I immediate searched for a sound sample via Google. Lo and Behold, the sample matched what I heard. I managed to receive, quite strongly, a NOAA transmission with a regular telescoping antenna.
So, I set to work. After referencing the RTL-SDR website article, I downloaded and installed WXtoIMG on my Mac. Once it was downloaded and installed, I had it go out, download new Keplerian elements for weather satellites and had the satellite generate new predictions. To my joy and amazement, NOAA satellites passed overhead everyday around 8 to 11 times. Using the prediction software, I would fire up my VR-500, and listen to see if the software matched predicted the satellite fly-by correctly, and it did! So now I knew my software could be relied upon. Next step – I ordered a new RTL-SDR dongle with a metal case and temperature stable oscillator. The NOAA transmissions are wider than what is typically passed through a handheld radio – so I ordered the SDR dongle to get full bandwidth reception of the NOAA signal.
I also installed CubicSDR – a straightforward SDR software program that can see the RTL-SDR series of dongles.
The software will control the SDR dongle and extract the audio from the transmission. The trick is to get the audio from the SDR software to the WXtoIMG software. You could record to disk, then have WXtoIMG process the audio file on disk, but I wanted something more “instantaneous”. What I needed was a”virtual audio cable” – to shunt the audio stream from CubicSDR to WXtoIMG. With a bit of searching, I came across the very useful project Soundflower – an open source virtual audio cable for the Mac. I installed Soundflower, rebooted the computer, and now I have another set of audio interfaces – input and output that can bee seen by audio programs across my system! Sweet!
So far, so good – we have software to control the SDR dongle, we have software to route the audio to other programs, and we have WXtoIMG – the software to decode the audio into an image and image processing with information overlay. What was needed now, was an appropriate antenna – and I just happened to have an old television rabbit ears antenna that was telescoping. The antenna leads can be adjusted each to 1/4 wavelength of the NOAA satellite transmissions and angled in such a way to get a maximum pickup on the RF. There are better antennas to use, but many an experimenter had excellent results with an angled dipole. Also, the kit I ordered from Nooelec included an RF balun that would allow me to connect the balanced antenna and feed line to the unbalanced coax cable to connect to the SDR dongle.
So with all of the hardware pieces available, and the software downloaded and installed, it was now time to build up the receive station. In Part 2, I go into detail as to how put the system together and test as I build the system up.
