More SSTV from the ISS

Like many others around the globe I spent yesterday attempting to receive and decode the SSTV transmissions being broadcast from the International Space Station by the Russian Cosmonauts.

The SSTV activity had been due to last three days starting on Saturday but commencement was delayed by the NASA space walk.

Receiving the signal and decoding is relatively straightforward due to relatively high power used (around 25W) however getting a perfect image is a challenge and dependant on a number of factors.

• The timing of the overhead pass. Due to the time taken to transmit the image and the three minute delay between each image it is possible to only be in reception range for the end of one image and the start of the next. 
• The ISS is moving quickly and so the transmission suffers noticeable Doppler shift. FM is more immune to the effect but for optimal performance adjustment of the tuned frequency is required especially on high elevation passes (more information).
• The ISS moves position, both in direction and elevation as it moves across the sky and will show up the peaks and troughs in a static antennas radiation pattern. This leads to bands of noise when the signal level falls. The use of a rotatable (and if possible tiltable) antenna (or even an handheld one) is the dirigour mode of operating satellites (and the ISS) for serious enthusiasts. 
• Noise and local interference will also obviously affect the image.

Mission Control

I opted a two pronged approach, the Yaesu FT857D connected to my rotatable four element YAGI which is mounted horizontally for SSB and the old TRIO/KENWOOD TR9000 was connected to the X50 dual-band collinear mounted vertically.

I had two copies of the MMSSTV program running on separate laptops The TR9000 was left running largely unattended tuned to 145.800MHz, while the FT857D was tweaked to the optimum frequency while the YAGI antenna was rotated to the correct azimuth during the pass.

All adjustments were done manually and I use the Orbitron program for prediction and under the Rotor/Radio tab the frequency and azimuth are shown and updated during the pass (as can be seen in the screen show below)

I missed the first low elevation at 11:07UTC, but was able to monitor and decode images on all the remaining passes during the day, with some excellent results, the images show the full images decodes on both radio set ups as a comparison.

FT857D - Yagi

TR9000 - Collinear

FT857D - Yagi

TR9000 - Collinear

FT857D - Yagi

TR9000 - Collinear

FT857D - Yagi

TR9000 - Collinear

FT857D - Yagi

TR9000 - Collinear

I was especially pleased when one of my best images was featured on the Amsat-UK and the Southgate Amateur Radio News websites.

What was slightly worrying and it also happened during the last SSTV activities were some operators transmitting on the downlink frequency even during a pass, what sounded like someone keying up was responsible for the single noise line on another perfect image. I even received an unexpected SSTV image, complete with a call sign while the system was waiting for the next pass. I won't publish it here as everyone makes mistakes.

The experiments are continuing today but I am in work so will just leave an automated set up running on the collinear.

Judging by the messages on social media these SSTV activities seem to have captured the imagination of a lot of operators and several members of my local club South Kesteven Amateur Radio Society (SKARS) had their first go with some excellent results and are hooked! The images can seen on the SKARS Facebook page

Long may the activities continue, hopefully started to transmit some live images from space.