[aprssig] Train tracks across the northern U.S.

Stephen H. Smith wa8lmf2 at aol.com
Wed Aug 28 23:41:36 EDT 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
> digi's).
> 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
Skype:        WA8LMF
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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