2015-11-12 Playing with slow scan tv transmitting 4 years ago
Amateur radio is a hobby with many sides, and I stumbled into a new one this evening. When I had time to try some radio propagation on HF bands I have access to was gone (ionospheric propagation on the 10 and 20 meter amateur bands usually drops as the sun goes down, more information at Radio Propagation article on Wikipedia). So, I had to try something else. I had a look at the 2 meter websdr available via repeater PI2NOS. I saw an interesting data mode on 144.500 MHz. Hearing it made me recognize it instantly from earlier experiments: slow-scan tv, which means sending images in small bandwidth (using audio encoding). I started qsstv which can decode these images. I used that software before to receive slow scan tv images from the international space station. Using pulseaudio I routed received audio from the websdr to qsstv. I wanted to play along (encouraged a bit by some fellow Veron A08 club members) so I tried sending images. It took a few tries to understand the template and macro use in qsstv. First the template did not expand so it was a 'CQ SSTV de %m' in the resulting image. Eventually I managed to send out a CQ and I tried to respond to someone. Who did not answer me, so no full QSO yet. The qsstv software uses templates to create an overlay over an image. The idea is to use text with macros in the template and select an image right before you start transmitting. I had a hard time finding some images to use so I ended up with some of my PD4KH images. The nice thing is that there is someone nearby always receiving SSTV images on 144.500 MHz: PD2PW has a website with the latest images. So I grabbed the results from that site to see how I did. Reception is very noisy: My 2 meter antenna is under the roof and I'm only transmitting at 10 watts.