How to work the APRS digipeater on the International Space Station ISS

Working the APRS digipeater on the ISS is not hard, but it requires some planning and knowledge. It took me a lot of reading, trial and error until I made my first successful contact some years ago. Maybe I can save somebody’s time a bit with this article. Would be great to get some feedback, if it was helpful or if there are any further questions.

1) Find out if the ISS digipeater is switched on and working
There are several sources that show the current status of the APRS digipeater on the ISS. First there is the ariss.org website with a lot of information about amateur radio on the ISS. There is one interesting page about the current station of the systems that can be found here: https://www.ariss.org/current-status-of-iss-stations.html. Unfortunately it’s sometimes a bit outdated and does not always show the current situation.

There are also some Twitter accounts following the ISS activity and it’s also always a good source for news and updates.

But the most reliable source is the website http://ariss.net/. This website shows a list of the last stations who where successfully repeated and received.ariss.net. The screenshot shows a list of July 22nd, 2019 where my message was repeated. The age of my message was 40.5 minutes at the time of this screenshot. If you see a lot of stations that where repeated within the last 1-2 hours, the digipeater seems to be online. If the age is a couple of days old, then it’s probably switched off (or broken).

Once you know that the digipeater is up and running we need to find out, when the ISS will be in range of your QTH the next time.

2) Find out when the ISS will be visible over your city.
There are many different websites that show the next passes of the ISS. The Nasa offers a website where you can see a list of the future passes for your city. Example for Hamburg is here: https://spotthestation.nasa.gov/sightings/view.cfm?country=Germany&region=None&city=Hamburg. If you search for “ISS position” at a search engine of your choice you might find several other sources. If you are the lucky owner of a smartphone (Apple or Anrdoid) you should install the App “ISS Detector” (https://issdetector.com/). This is a very powerful app that you can use to track the ISS and many other satellites. It uses the compass and tilt sensor to show you the exact position of the ISS during a pass. That is very helpful to spot it and to point the antenna in the right direction.

3) Configure your radio
Now you know that the digipeater is and and running and that the ISS will be in range, soon. Now it’s time to configure the radio. I will just give a short summary as I assume that you already know the APRS basics and how to change the config on your TRX. If not, just leave a reply and I will try to help.

Frequency: 145.825 MHz
Path: ARISS
Status-Text: Something nice
TRX-Power: 5 Watts should be enough.
You don’t need to take care of Doppler shift on 2m.
Unmute your radio, so that you can hear the APRS messages

ARISS is an alias which is used by the ISS and some other satellites. The ISS digipeater will replace ARISS with RS0ISS* when your message is repeated. If you receive this, you know that you made contact 🙂

4) Chose the right antenna

The best success rate I have with a LPDA for 2m and 70cm. I have one with a tripoid mount which is very useful as it allows you to have both hands free to control the radio. I always made some successful contacts using a mobile antenna with a magnetic mount on my car. I also tried it a couple of times with the normal handheld antenna, but I was not very lucky there.

5) Make contact!
Allright, everything is set up. Battery is charged, antenna is connected, Settings are double and triple checked and the ISS is coming closer. Sometimes you can see the ISS directly which makes it very easy to point the antenna. Otherwise just use the App to find the current direction. If everything is set up correctly and the digipeater is working, you should hear the first packets and if the signal strength is good enough your radio should be able to decode them. Now it’s time to send a beacon. Shortly after you sent the beacon you should receive your own message back. If you check the path of the packet, you should read RS0ISS* instead of ARISS. Now you know: It worked! You can now check https://ariss.net or https://aprs.fi to see if there was a Sat-Igate that received your message.

6) Fair use:
You are not alone. Like you there are many others who want to work the ISS. So please don’t flood it with messages. If you received your own message you know: It worked. There is no award for the most repeated packets during one pass (at least as far as I know). So please practise fair use and give others the chance to enjoy the contact with space.

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