Accessing the ISS Digipeater

image_product01With a long weekend, and a major project at work behind me, I had a tiny bit of breathing space to play radio this weekend. What I should have been doing is putting in a couple of hours on the AllStarLink for my club (currently at about 30% finished). What prevented this was a new toy scored second-hand from eBay that arrived this week – a Kenwood TH-D72A handheld.


qslI grabbed this off eBay, the main attraction being it’s APRS capability, including: built in GPS, stand alone digipeating, and the ability to plug it into a PC and use it as a TNC. My first big plan for this, since I’m miles from anywhere, was to use it to get my staion on the ARISS map by having it digipeated by the International Space Station

One of the ISS experiments is Amateur Radio on the International Space Station (ARISS). Most of the astronauts are licensed amateurs – mostly because they occasionally use an amateur radio on board to make scheduled radio contacts with schools for PR reasons. This is a good deal for NASA as they can depend on local amateur radio operators to turn up a school and set up the ground station and help the students run it. It’s a good deal for amateur radio because we get some favourable PR from being associated with such a cool deal.


ISS Russian Service Module showing amateur radio location and VHF antenna


Very occasionally there will be an active amateur on board with some free time and they will make some voice contacts, last year a UK guy was thrilled to make a contact from his garden shed. Sometimes to commemorate an event, they will run SSTV from the radio. The rest of the time, one of the radios is left in “digipeater” mode to repeat APRS packets. mapAPRS (Amateur Packet Reporting System) packets sound just like a half-second’s sequence of musical notes when you hear them on the radio. They can contain all sorts of data to do with what’s going on in your local area – which repeaters are available, which hams are driving around, and even data from weather stations.

digipeatingA digipeater takes in an APRS packet of data, inspects it then re-transmits it. The purpose of this is to allow these little packets of information to travel further. Some digipeaters are on tops of towers or mountains, some just at peoples houses.

The digipeater on the ISS is obviously a long way up, so it covers a huge area – probably a couple of thousand kilometres across. Getting a packet up all that way can be more challenging than a local repeater; the ISS can be a long way away, and it can be right overhead – a place most antennas have a large null. In addition to these two factors, the pass can be quiet short – usually less than about seven minutes good working.

I use the website to work out when I’ll have a good pass. When looking at the data for a pass, the first thing I’m interested in is the altitude in degrees. 90º would be right overhead. I usually don’t get excited about a pass unless it’s going to be above 20º – much lower than that and it’s behind obstacles and deep in the terrestrial noise.

stationI had a go at a pass on Saturday – got all set up, watched a live track of the ISS on a website, listened with my squelch open and heard nothing. I knew that Brian VK6TGQ was beaconing from Bunbury, so to hear nothing meant I had a problem with my setup. I carefully looked over everything. Eventually I realised I was on the wrong frequency – 146.850!

IMG_1554There was another good pass on Sunday. I could hear other stations’ packets being repeated from just below 20º, but not clear enough for my radio to decode them. As they got clearer I tried a beacon, but still no luck. Then one the way down again at around 45º I heard some really clear packets – my radio didn’t decode them but I thought this was my best chance. I manually beaconed a packet. less than a second later, my radio chirped and updated the display to say my position had been repeated by RS0ISS – the call-sign of the digipeater radio in the Russian module of the International Space Station.

A few seconds later, Brian saw me on the ARISS map. It’s also possible to extract the raw packet from that site:

00:00:05:21 : VK6MIB-7]DDF9X2,RS0ISS*,SGATE,WIDE,qAR,VK6PII-6:’.80l -/]First try! =

This shows that my packet was ‘gated’ by VK6PII (Chris) at his station in Perth. Brian and I are not sure why Brian’s station didn’t also get a clear copy of my packet, he did gate one of Chris’s.

Anyway, this counts as success, and is probably the shortest purchase-to-successful-use of any of my gear so far. I’m looking forward to getting a handle on everything this radio is capable of.


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