Based on some years-ago testing, I concluded that using 5-watts for APRS position beacons for tracking during public service events was pretty much a waste of time. But I was wrong. Sorta.
The reasons: Low power and congestion on the national APRS channel, 144.390, caused my testing to have more lost packets than good ones. It was possible to drive a number of miles between position fixes captured on APRS sites and apps.
Granted, a very close digipeater or just a receiver at net control might hear packets that don’t get repeated thanks to being close, but I was still unconvinced.
Last years’ testing, using a two digipeaters and an empty channel worked far better, but even two mobiles set to smartbeacon at short intervals got very congested.
These experiences made me not very interested in using APRS, but I keep getting dragged in, mostly because I own a lot of gear.
APRS can work
Several weeks ago, I was part of the APRS team for a bicycle ride in Stockton. This was a 100-mile course with shorter courses embedded within it. The course was long and narrow but very flat. The main “hills” were levees, but they could block signals in some cases.
The course, in the San Joaquin River Delta, was about 40 miles end-to-end but only 15 miles across. Needless to say, the start/finish was at the south end of the course and the turnaround at the north. Here is a link to the course map (PDF).
Several days before the ride, Mike, KJ6KDJ and I drove the course, sending packets about every minute to see where we had coverage and how many packets are missed. I used a Yaesu FT1D and a small cartop antenna for this test. Power out was 5-watts.
It turned out there was only one short stretch that seemed to lack APRS coverage and enough packets got through that I was easily able to follow myself on an iPhone APRS application. Of course, the app could also send my APRS packets, too.
On ride way, we ran five mobiles, each with a 5-watt APRS station. Net control was very happy with the APRS locations provided and my occasional checks of the iPhone app confirmed that the system worked well enough to send the right unit to the right place when needed.
A few caveats
The reasons this worked so well:
- Elongated course spread the mobiles across a wide area.
- Using only five mobiles meant their locations needn’t be super accurate to be useful.
- Super flat course.
- Digipeaters that were close to the course provided needed coverage.
- Mobiles were almost always moving, looking for riders needing assistance, so position reports were helpful.
- Most important: We drove and tested the course in advance. By the start of the ride, I had decent faith that our project would be successful.
- Asking mobiles for their location would have been just as effective (with only 5 mobiles, 15 would have been different) and a lot less work.
- Besides, the mobile were speaking often enough that it was easy enough to keep track of them in control operators’ heads.
- On a smaller course or with more mobiles, radio congestion could become an issue.
A Party Game for Hams?
I was impressed because the APRS system worked and net control felt it contributed positively to their conduct of the event. I am still of the opinion that APRS is essentially a party game for hams, but it is a came we can win, at least occasionally.