–legacy post: originally written in high school–

The International Space Station has a 2m rig onboard. Occasionally the ISS crew have voice contacts with the ground using their 2m radio, however, they almost always occur over europe. The rest of the time the 2m rig is set up for digital communication.

First I had to build an interface between my laptop and my radio. Digital communication works by encoding data (text or images) as sound, to broadcast using the radio. Cables go from the earphone and mic jacks on my radio to the earphone and mic jacks on my laptop. Software encodes, decodes and keys the radio automatically. I built a little interface on veroboard and surprisingly it worked!

Next I needed an aerial. Half the fun of the ham radio hobby is building your own aerials, so I found a design for a J-pole made from TV twin lead, and built it.

Finally, time to make contact. The first thing I tried was to digipeat my aprs beacon via the ISS. An aprs beacon is simply two lines of text including your gps coordinates and a short message. The software on my laptop would convert the text into a sound clip, which would then be broadcast by my radio. With any luck the radio on the ISS would hear my message, and rebroadcast it from space. Now bear in mind that my radio has a measly 2W of power, and my aerial was built without an SWR meter.

ham radio3

I threw my jpole into a tree and set up my communication station in the garden.

iss aprs

SUCCESS! UISS is the software used to encode data into sound. The first two lines of text are the ISS’s beacon, which my radio received. Next I sent my beacon, which was repeated by the ISS (red).

Next it was time to try to get into the ISS BBS. This is a sort of answering machine. You can leave a short message on the ISS, which can then be read by the ISS crew (unlikely), or other ham radio operators around the world. Since only one operator can connect to the ISS BBS at any one time, I am fortunate that here in South Africa, I have very little competition from other operators.

You can only communicate with the ISS while it is overhead, and since it is only overhead for a few minutes a day, you have to be quick. Unfortunately packet radio is very slow, and so the process can be tedious. However, after being cut off several times by the ISS going below the horizon, I managed to get my short message onto the ISS message machine. The next day I reconnected to the ISS and downloaded the list of stored messages, just to double check whether mine was indeed there. To my surprise, not only was mine there, but there was a reply! A ham radio operator in Argentina had also downloaded the list of messages from the ISS, had seen mine, and replied via another message on the ISS. Amazing! Unfortunately I never got the chance to download the complete message.



Here you can see a reverse chronological list of the message headers stored on the ISS, as received by an amateur radio organisation in Argentina. My message (which i sent twice) can be seen, followed by a reply from LU8YY.