[aprssig] APRS on HF
Stephen H. Smith
wa8lmf2 at aol.com
Sun Feb 20 16:13:32 EST 2011
On 2/20/2011 7:00 AM, David Dobbins wrote:
> I don't believe the picture Stephen has painted of VHF infrastructure in the
> west is as bleak as he indicates. I concur there are still some secondary
> areas (off the primary lines of communication) where there is "less"
> infrastructure, but for the most part I would say there is generally good
> coverage for our half of the USA and Canada.
> My primary summer mode of transportation is motorcycle, and my little TH-D7A
> in the saddle bag seems to do just fine on the roads my motorcycle likes best
> of all, anything that is NOT a freeway. If I'm really in our lovely
> wilderness and not getting any signals into the system for another 30-45
> minutes, who cares? But for the most part I can ride around most places in
> the west and manage a regular flow of burps into the system. The Snake River
> in Idaho is pretty well covered giving the immensity of the nearby mountains,
> and the expanse of central Nevada is extremely well covered by a few remote
> mountaintop digis. If you've traveled the "Loneliest Road in America" across
> Nevada you'll know what I mean.
The VHF APRS coverage in the interior west is almost exclusively due to a
handful of "super-wide" digipeaters located on extremely high mountain-tops
towering 6 to 8 thousand feet (2,000-2500 meters) or more above the areas they
cover. As long as you have a true line-of-sight path to these peaks, you can
hit them easily from 100-150 miles (160-250 KM) away.
The placement and coverage of these digis favors the Interstate highway system
(I- numbered routes) and the major secondary (US-numbered routes) roads.
BTW, the "Loneliest Road" is US-50 running east-west across central Nevada.
The moment you add ANY kind of additional path loss (forests, entering a town
with buildings blocking the view of the distant mountain tops, getting off the
beaten path where smaller mountain ranges block the view of the farther-away
major ones, heading into canyons, etc, the coverage disappears very quickly.
For example, I-15 from San Diego in far southern California to beyond Salt Lake
City, Utah has continuous VHF coverage spanning a distance of over 600 miles
(1000 KM). Drive US-89 in Utah which more-or-less parallels I-80 about 50-80
miles to the east, and you have no coverage at all for long stretches (it's
behind a smaller mountain range hidden from the digis covering a lot of I-15.)
Surprisingly, one of the biggest coverage holes in the US isn't in the western
mountains at all. Heading east, you descend out of the Front Range of the
Rocky Mountains in Denver or Colorado Springs onto the endless empty flat
grasslands of the High Plains. Once you get about 60-70 miles east of Denver,
there is no coverage at all on Interstate 70, 76 and 80 for 300-400 miles,
until you get to eastern Nebraska or central Kansas. I.e. once there are no
mountains to support "super-wide" digis with monster coverage, you are
dependent on a digi every 20 miles or so. But you just don't get digis every
20-30 miles in places with such low population density.
Another place with surprisingly poor coverage is the rural parts of the US
south-east (a.k.a. "the old South"). The coastal south from New Orleans
through Mississippi and Alabama to Florida have fairly good coverage, due to
the steady scattering of cities. Florida itself has almost continuous
coverage due to the development and population along nearly all of it's coastline.
However, get more than about 50-100 miles inland from the Gulf Coast in most of
the south, and coverage almost completely disappears due to a combination of
relatively low population density, continuous thick forests, and flat terrain
with no mountains to elevate digipeaters significantly above the surrounding
terrain. Again, you get islands of coverage in the mid-size and large cities
like Atlanta, Mongomery, Birmingham, Jackson, etc with many many miles of
nothing in between.
In these types of places, trying to "bludgeon" the lack of coverage with long
digi path settings accomplishes absolutely nothing, since if there isn't even
a first hop to be had, the additional hops will also do nothing. Then when
you DO get a clean path to a mountain top "super-wide", a path like WIDE3-3 or
WIDE1-1,WIDE2-2 spams nearly the entire west, because the super-wide at 6,000+
feet is within effortless range of other "super-wides" hundreds of miles away.
Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: WA8LMF or 14400 [Think bottom of the 2M band]
Home Page: http://wa8lmf.net
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