Friday 27 September 2013

APRS IGate - "If you build it they will come"

The 2013 National Hamfest is taking place this weekend, it is held over two days at the nearby Newark Showground. I will be visiting tomorrow (Saturday) as work commitments prevent me attending today, so no doubt all the best second hand bargains will be gone!

Seriously I am looking forward to it now that I am a proper licenced radio amateur. The Hamfest has been held at this venue for several years and always gives me the opportunity to hear the VHF/UHF bands full of local chatter. Normally the chatter consists of operators trying to give each other directions! The showground isn’t very well sign posted from the local approaches.

In previous years they have a had a call-in station operating on the usual channel (S22) 145.550MHz, but today it wasn’t in evidence well not at 10:00am when I listened in, instead there were several local operators chin-wagging with the occasional calls asking for the rally call-in.

This year the Hamfest have enlisted the services of the BritishAmateur Television Club to give live internet television feeds. Go to the live eventspage and there are two streams and currently a third from GX3RCM available.

One thing I hinted at previously was to experiment with APRS and I really wanted to get an APRS IGate set up in time for the weekend as I was expecting a number of the attendees at the Hamfest would be using it.

From the Wikipedia page 
"Automatic Packet Reporting System (APRS) is an amateur-radio based system for real time tactical digital communications of information of immediate value in the local area. In addition, all such data is ingested into the APRS Internet System (APRS-IS) and distributed globally for ubiquitous and immediate access. Along with messages, alerts, announcements and bulletins, the most visible aspect of APRS is its map display. Anyone may place any object or information on his or her map, and it is distributed to all maps of all users in the local RF network or monitoring the area via the Internet. Any station, radio or object that has an attached GPS is automatically tracked. Other prominent map features are weather stations, alerts and objects and other map-related amateur radio volunteer activities including search and rescue and signal direction finding."

There are two short video on youtube which describe the APRS system and the role of IGates, an IGate is basically a receiver station that puts locally received messages into the APRS-IS system.

I have a Baofeng UV-3R handheld transceiver which I have pressed into service. I don’t have a dedicated TNC so am using the compute sound card to receive and send audio to the transceiver via the handset connector and am using the AGWPE as a software modem/TNC that is used by the APRSISCE/32 client to create the station.

It should have been straightforward as I already had an eQSO interface which should have provided an isolated audio interface and control of the PTT on the UV-3R, all I had to do was create a suitable connecting lead.

During the commissioning the station seemed more than capable of transmitting messages but it wasn’t receiving anything, checking the audio coming in to the PC and I was getting virtually nothing! The interface was dismantled and the signal scoped. Oddly it seemed the UV-3R really didn’t like the isolating audio transformer and this seemed to shorting the output from the transceiver, so now at present it is just directly connected.

Sadly while using the scope to see the signal the ageing scope decided to commit suicide in a loud bang and cloud of acrid smoke, oddly despite the pyrotechnics it was still working till I turned if off and now it won’t turn on! I suspect a capacitor in the switch mode supply has died in spectacular fashion.

Anyway I digress, having got the system working properly late last night it is currently running and has indeed received a number of stations this morning as made their way to the Hamfest.

The UV-3R probably isn’t the best choice as a receiver as its audio is pretty dreadful but it seems to work, it is connected to a generic X-50 antenna stuck on the top of a 4 meter pole. The pole is in fact a 5 meter telescopic painting pole costing less than £16 from B&Q.

I haven’t fully extended the sections as the joints could be potentially weak, but it is anchored to a metal fencing pole and then with three guy ropes it seems sturdy and has stood out all week, just lowered down slightly when not in use.

X-50 in the garden
You can see a map of the current APRS stations at my station statistics can be seen here

This was a snapshot of the map earlier showing the cluster of stations at the showground

Quite a few operators are using their smartphones rather than radios to update their position. I have installed APRSdroid on my phone (not free from Google Market, for free version go to developer website see Pete's 2E0SQL comment below, and you need to be a licenced amateur with a valid passcode) but it gives me a warm feeling to know my humble set up has allowed some people to show up at their destination using their 'proper' radios.

The shack - APRS setup on the left hand side


Peter said...

Just a quick note to say you can get APRSDroid free by downloading the APK from the developers website at

Of course buying on the Play store means automatic updates and you help further development but its an option!

Pete, 2E0SQL

Andrew Garratt said...

Thanks Pete, missed that and I should have pointed out it is only £2.95 less than the price of that pint I owe you..