[aprssig] Train tracks across the northern U.S.
Stephen H. Smith
wa8lmf2 at aol.com
Wed Aug 28 22:41:36 CDT 2013
On 8/28/2013 10:20 PM, Andrew P. wrote:
> Greetings, all.
> 1. There are huge spans with no digipeater/I-gate coverage at all along the
> route. In the screenshot, note the places where I was able to report position
> over Internet connectivity but not by 2m radio (obvious because of no nearby
> 2. The coverage for AT&T cellular service was better than for 2m APRS (I could
> maintain an APRS-IS connection over a wireless hotspot in places where I
> couldn't hit a digi), but still had holes.
Not too surprising considering that there are over 270,000 cell sites in the
US, compared to a few hundred to a few thousand APRS digis in the whole US &
Canada. [Many of these cell sites have 2, 3 or even all 4 of the major cell
carriers (Verizon, ATT, Sprint & T-Mobile) co-located.]
Not to mention that the route from Chicago to WA passes largely through some of
the least populated areas of the US, contributing to even few digis per square
mile than average. Ham density (and therefore digi density) tends to follow
population density in general.
Further, digi coverage tends to favor highways, especially the Interstate
System. I have noticed this for years, especially driving around the western
US. The Interstate system has almost continuous coverage, but veer off the
Interstates in the interior west, onto secondary roads behind a mountain range,
and you "drive off the edge of the earth" APRS-wise.
Note that the rail route tends to hug the Canadian border along most of it's
route through western Minnesota, North Dakota, Montana, and Idaho, while the
nearest Interstate corridor along I-94 and I-90 is 100 to 200 miles south of
the rail line.
For over two decades, I have been driving the route between Chicago and Los
Angeles (I-80 to I-76 to I-70 to I-15). The eastern part of the Midwest
(Illinois, Iowa and eastern Nebraska Omaha-to-Lincoln) have excellent coverage.
Once you hit the Rockies west of Denver, you have pretty much continuous
coverage to Los Angeles, thanks to a handful of monster "super-wide" digis on
7-8-10,000 foot mountain tops throughout Colorado, Utah, Nevada and California.
But there is about a 250-300 mile APRS "black hole" in the middle. Once you get
west of Grand Island, Nebraska there is NOTHING until you start hitting digis
in the Front Range of the Rockies, beginning about 60-70 miles east of Denver.
(This is when I switch to 30 meters HF APRS that can get out anywhere!)
In the flatlands of the Midwest and High Plains, the coverage quite precisely
follows population density. In the west beyond the Rockies, super-wide digis
offset the lack of population. The low population density between Denver and
the West Coast ensures that these super-wide digis with 100-150-mile coverage
radius aren't completely overloaded with hundreds of dumb trackers
smart-beaconing their every turn on the way to the local 7-11!
Stephen H. Smith wa8lmf (at) aol.com
EchoLink: 14400 [Think bottom of the 2-meter band]
Home Page: http://wa8lmf.net
Long-Range APRS on 30 Meters HF
High Performance Sound Systems for Soundcard Apps
"APRS 101" Explanation of APRS Path Selection & Digipeating
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