MAI-75 SSTV Event
As usual, there was all of 4 days notice for an SSTV event.
This is a pretty short event and optimized for passes over Russia, as all to often it happens. However as usual there were some passes over New Zealand, with three that had a high enough elevation to make it worth capturing. Too low and the signal to noise ratio means that you can just about hear something but nothing is decodable.
I was pleased too as it gave me a chance to try out my new antenna for SSTV capture with an increased gain set as I’d realized from the previous event that a bit more signal would help.
The first pass was a disappointment as I had nothing that would decode, even though I could hear something there in the noise. I checked quite a few things, including that I’d got the gain right, but there was nothing obvious. Then I spotted the LNA (Low Noise Amplifier) which was sat on my desk, not connected to the antenna! No wonder it wasn’t working as it should. At least with a quarter wave antenna the vertical is not electrically connected to the ground plane elements, so I wasn’t seeing a DC short as there was power being sent from the SDR to power the LNA. This can cause damage to the SDR.
So I was down to two passes, hoping I’d not messed up anything else.
Not the best ever images, but still pretty good apart from where I was clearly seeing RF noise (which seems to be a constant problem, especially with Meteor M-2 image captures).
The next pass had really poor signal quality with a lot of noise, so the end result was just a small, partial capture, proving that just building a tuned antenna for SSTV wasn’t a magic bullet.
I also found that when listening to the signal there were obvious noise sources including:
- What sounds like a human voice – is someone transmitting on a nearby frequency?
- Pager like sounds of short duration – 145.8MHz isn’t a normal pager frequency, unless someone is transmitting pager data relatively locally?
So overall, other than an obvious mistake I’d got some better images than using the QFH, but room for improvement.