Archive for August 14th, 2010
I was running my GPS-to-APRS tracker while on a bicycling vacation along rail-trail paths around southeast PA. I expected good coverage in urban areas and not much in the woods, which is pretty much how it worked out.
Here’s a plot of my track (from aprs.fi), with superimposed half-size PHG (Power-Height-Gain) “circles” for the digipeaters that caught my signal. Clicky for many more dots.
The first part of the ride, from BB62 in Camden NJ to Pottstown PA, had good coverage.
A bus jaunt from Pottstown to White Haven, just north of I80 along the Lehigh River gorge, accounts for the abrupt jump. I dropped off the face of the earth at White Haven, riding south along the Lehigh River to Jim Thorpe, then along some undeveloped trails to resurface just north of Allentown.
Strangely, there are no points east from Allentown to the Delaware, then south along the river & canal to Trenton. We stayed overnight on Bull’s Head Island where, as nearly as I could tell, there were no other APRS signals at all.
A plot of all the APRS activity (and, thus, all the active digis) for a different 24 hours shows the gaps in coverage match up fairly well with where I wasn’t heard. These are also half-size circles, but don’t take topography into account. Notice that the trails along the Delaware run right through the no-coverage zone!
I’m not sure why the digis caught me going into Allentown and not going out, but the vagaries of RF propagation remain inscrutable. Even if the digipeater could receive a clear signal, a collision between two transmitters can kill both packets stone cold dead. In addition, I’m using 100 Hz tone squelch and some receivers may not decode packets with tones.
Another possibility is a path (WIDE1-1, WIDE2-2) that allows only two hops to an Internet gateway. In those remote regions, it may well be that I should have had a path allowing three or four hops. However, I wasn’t hauling along all the programming gear to tweak the TinyTrak3+ on my bike. If I lived around there, I’d have a better appreciation of what’s needed to get out of the valleys.
In any event, it was an interesting exercise…