wythall radio club

having fun with RF

Signals from Space with a Handheld

September 22, 2023 By: Chris G3YHF Category: Club, Fun, News, Training

The ISS (international space station)’s digipeater can be heard with a 2 meter handheld when one of the ISS passes is overhead.
And if you can connect your 2m FM rig to a computer, you can send and receive messages through it – and receive the special ISS QSL card!
Now is a good time to try as the ISS is passing over the UK at a good elevation twice most early evenings.
Find the ISS pass times HERE – remember to add 1 hour as times are UTC.  Ideally, look for 70° or 80° elevation when ISS is passing close to overhead.
The live ISS locator is useful to track its position and digipeater footprint.
Tune to 145.825 FM with squelch OFF and listen for the short bursts of data.  You will only hear these for a couple of minutes during each pass.

The contents of data packages received by the ISS are instantaneously retransmitted by the digipeater and received by one of the SATGATEs where they are automatically uploaded to the ARISS web site HERE along with the list of stations whose transmissions were received and maps of their locations.
Only short messages can be sent, and here are some examples from earlier this evening:
00:00:01:12 : G0GOO]CQ,RS0ISS*,qAR,ED1ZBF-3::G7HCE :QSL and 73 via ISS
00:00:01:32 : G6UQZ-1]APDW17,RS0ISS*,qAU,DO6DD-10:!5204.75N/00034.94EyPHG200073 de Andy in Clare, Suffolk
00:00:01:39 : G3YHF]CQ,RS0ISS*,qAU,DO6DD-10:=5226.15N/00152.30W-IO92BK 73 de Wythall RC {UISS54}
00:00:01:41 : RS0ISS]0P0PS3,APRSAT,qAR,ED1ZBF-3:’v&l SI]ARISS-International Space Station=
00:00:01:42 : G7HCE]APK004,RS0ISS*,qAR,F1ZRP-3::G0GOO :Copy 59{5
The highlighted message is the one I sent this evening that was received and retransmitted by the digipeater after 6 or 7 attempts!
It gives the age of the retransmission, my call, the callsign of the digipeater – RS0ISS* is the Russian ISS call sign, DO6DD is the German SATGATE station that received and uploaded the packet to the ARISS site, and then there is my message: my APRS location in lat and long and Maidenhead square, and a few words of greeting!  The ‘ – ‘  instructs the ARISS site to add my QTH to its map.
Occasionally, the digipeater is temporarily shut-down for spacecraft operational activity like a spacewalk.
To send a message through the digipeater, connect a rig that can transmit 2m FM to a computer.  The rig will need an internal soundcard or if not use an interface like Signalink.  
I use my Yaesu FT7800 mobile rig on 5 watts with Signalink and a collinear. 
I also have an old Kenwood TH-D7 handheld with internal TNC and APRS functionality – this puts out 2.5 watts and I’ve been received by the digipeater again using my collinear.
Then download and configure UISS , which has been designed for communicating with the ISS digipeater.  Configure so it talks to your radio.  Then set ‘path’ to ARISS and add your APRS data and a short text.
There’s lots of on-line advice on how to set up UISS and use it to send a message – e.g.  on the AMSAT site
DON’T USE HIGH POWER!  ISS is line of sight, so 5 watts to a collinear will work very well.  High power will put exessive demand on the ISS rig’s batteries and block other stations from using the digipeater. 
The digipeater is simplex and lots of European stations will be calling so it may take several goes to get through.  On the current west to east trajectory of ISS, it’s best to try early on a pass before it’s in range of continental Europe
When your message is retransmitted by the digipeater, it will often appear as a highlighted message in UISS.
However, you may not receive this retransmit due to fading or other factors causing even one bit of data to be lost, so affecting the checksum.  
So it is always best to search for your call on the ‘Amateur Radio Stations heard via ISS’ page at ariss.net as a ground station operating a SATGATE may have received the retransmission and automatically uploaded it to the ARISS site.
Wythall Radio Club members had a go with conducting a brief QSO using the digipeater a couple of years ago, and two of us used it to score points in our Christmas Contest.  
Have fun!