SSTV from the ISS (February) - MAI75 experiment

Geschrieben von Tysonpower am {{ "2017-02-15T17:00:44+00:00" | date "longDate" }}

Every few months, the ISS transmits pictures to be received from hams around the world. They are transmitted with a 3-minute gab between them on 145.800mhz. These images are like postcards that you can collect. For each event there are 12 different ones, that can be collected, which mostly show historical moments of space flight. The SSTV, that comes from the MAI75 experiment, was last active in December 2016, where i unfortunately had no time to receive something. At an Event before, in August 2016, I received 6 images with a DIY QFH antenna that was connected to an SDR and LNA.

The ISS was scheduled to transmit SSTV for the last two days as the February event. On Monday there was no Signal from the ISS at all, as far as I know, they had problems setting up the transmitter on the ISS. On Tuesday there were some people on twitter that got a SSTV signal from the station, so the transmitter was finally active!

I had two high passes of the ISS (max elv of 75° and 78°) that I could get after work. So I got to the field and got a very strong Signal at the first pass that resulted in two images that were not that great. The audio was quite low, even when the Signal itself was very strong (up to 49db SNR!), what was also reported by a bunch of hams on twitter. It seems that the transmitter on the ISS had a problem with low audio. Another problem for me was, that the first transmission stopped at around 40°. Because of the 3min gab, the second one began shortly before the ISS gets out of range.

Around 90min later I got out again with my SDR (RTL-SDR.com v3), LNA (LNA4ALL in custom metal case incl. a battery) and DIY Yagi Antenna for the second pass. After the ISS was in range, I was wondering why I get no Signal at all. MY first thought was that the transmission was already shutdown, because the pass was right at the end of the scheduled time. I switched my handheld radio (with a whip antenna) on, when the ISS was at max elv. and i heard a Signal! I pointed my Yagi on the ISS again, but i still got no Signal....so something must have failed in my SDR setup :(

After I checked that the LNA was on (green led on the metal box) I packed everything as fast as I can and headed home because I had the recording of a UK Websdr on. I was able to extract a part of the picture, that I would have received perfectly if there wouldn't have been a problem with my setup.

After testing the SDR and Booster, the only thing that could have failed was the Yagi...and I was right. One solder joint in the feeder that connects to the shielding of the cable had broke off. It was fixed in 30s with a soldering iron, but I got no image because of that, what was really annoying. To prevent this from happening again, i now fixed the cable with hot glue to the feeder case (3d printed part), so any pull on the cable doesn't stress the solder joint.

I hope that the next event will be soon and that I get more and better images from space.