Satellite SSTV Modes

Everyone would like to receive a perfect image without noise and with high definition. But SSTV is a compromise mode, trading off quality for bandwidth and time. On Satellite SSTV, especially with the Low Earth Orbitting Satellites (LEOs), time is in short supply, and since a high definition picture takes longer, the transmission may well exceed the time of satellite visibility. With a typical 10-15 minute LEO pass, 4 S2 pictures (1 minute each), 2 S1 pictures (2 minutes each) , or 1 Scottie DX (4 minutes) can be exchanged + making contact, talking, setup, etc.

Another problem, especially with the LEOs, is Doppler. Most Satellite SSTV operators are familiar with HF SSTV, where the signal can rather easily be tuned to frequency and expected to stay there. Doppler shift creates unexpected effects on the different SSTV modes.

The original W0LMD image picture below was captured from an IBM Net Camera into ChromaPIX software running full duplex. It was the sent up to the LEO satellite FO-20 on 145.920 Mhz. The other pictures were received back on 435.880 by W0LMD.

                       

                         

Off frequency (not tuning in the 1200 Hz pulse at exactly 1200 Hz) can adversely affect the color registration of certain SSTV modes. The Scottie modes will just change intensity with off frequency.

                       

   The Scottie 2 picture below was received near the end of the pass with high doppler.

                

The last moments of a satellite pass are characterized by a weak satellite signal and QRN from power lines & ignition sytems.