Background

As its name suggests, Amateur Radio on the International Space Station (ARISS) is an organisation created to promote interest in communicating with the International Space Station (ISS) via ham radio. To mark the 20th anniversary of its operations on the ISS, ARISS conducted a slow-scan television (SSTV) event in the last week of December. The ISS would transmit SSTV images continously from 2020-12-24T16:40:00 until 2020-12-21T18:15:00 on 145.80 MHz FM.

I heard about this via a Reddit thread and learnt that my Baofeng UV5R was likely capable of receiving transmissions from the ISS using the stock antenna. The video from the Reddit thread is embedded below. I was intrigued and figured this would be a good opportunity as any to get back into ham radio. After doing some research on the subject I identified that I would need a few things before I could get these pictures from the ISS:

• A way to track the ISS so I knew when it would pass overhead.
• A way to decode the SSTV audio into an image.

There are several websites that offer tracking information about the ISS and other satellites. Some of these include the AMSAT pass predictor, and N2YO’s tracking page. However, I wanted something that I could install on my laptop and that I wouldn’t have to rely on an active internet connection to use. I settled on Gpredict which does a good job of providing detailed pass information for virtually any satellite.

The SSTV images are transmitted from the ISS as audio. An SSTV image is made up of a header and the colour data. The header identifies the type of encoding used (e.g. Scottie S1, Martin M1, Robot36, etc) and the colour data does what it says on the tin. The encoding determines the resolution of the image and the format of the colour data. The ISS transmits its images in PD120 mode which has a resolution of 640 pixels wide and 496 pixels high. I decided to use the popular Android app Robot36 to decode the images with my smartphone. If using a computer to decode the audio, one could use RX-SSTV, QSSTV, or a similar program.

Getting the Images

Now that I had everything that I needed I started up Gpredict and found that the next ISS pass was in about an hour. There were only three days left in the event so I was eager to start getting some images as I had heard that it can be many days until the next pass depending on one’s location.

My handheld has a simple rubber-duckie style antenna and I would have expected to have to hold the radio horizontally in order to pick up a decent signal. This proved to be mostly true, however I found that I was still able to get a signal by holding the radio upright. By holding my smartphone near the radio with the Robot36 app running, I was able to received the following image. Note the strip of green static that occurred due to “losing” the satellite in the sky.

I couldn’t believe that it was as easy as that! For the remaining three days of the event I managed to get another five good SSTV images (and some odd looks from my girlfriend’s neighbours). I found that I wouldn’t be able to receive any transmission until about 90 seconds after the acquisition of signal (AOS). This could be explained by the trees and buildings obscuring the line of sight to the ISS. Doppler shift may also have played a part in not getting a signal early on.

Often I would receive the tail end of one image as it came over the horizon and would then need to wait the two minute interval before the next image was transmitted. This allowed me to always get one image per pass.

The Remaining Images

Conclusion

I submitted the fourth image to the gallery as it was the clearest one, however I believe it has too much static to be accepted.

The ARISS SSTV Blog reports on planned radio activity on the ISS and provides a good source of related information. I’ll certainly be keeping an eye on this for upcoming events (there’s an atom feed located here).

Next time there’s an event on I’d like to have a good antenna to use and would consider driving up to the hills instead of standing out on the street.