[aprssig] unusual Terrestrial APRS propagation

Robert Bruninga bruninga at usna.edu
Tue Sep 1 10:07:06 CDT 2015


I agree, there is no better tropo indicator (or meteorscatter) detection
system than APRS.  With 20,000 transmitters all over the country running
continuously, even a few seconds of enhanced propogation will appear on the
APRS network while the Voice Operators may be waiting72 hours for the
weekend.



Of course, someone in a rural area that can only hear one local digi will
hear a LOT more tropo than someone in a busy APRS area where the channel is
always busy…



In fact, people is remote APRS areas my feel lonely with the lack of
activity, but any activity they DO see can be very exciting with enhanced
propogation…  And now is the season for tropo.  I hear it every day in
Maryalnd in the mornings when I hear the FM radio stations all jumbled
coming to work…   bob



*From:* aprssig [mailto:aprssig-bounces at tapr.org] *On Behalf Of *Ev Tupis
via aprssig
*Sent:* Tuesday, September 01, 2015 9:20 AM
*To:* TAPR APRS Mailing List
*Subject:* [aprssig] unusual Terrestrial APRS propagation



*Sent:* Monday, August 31, 2015 8:47 PM
*Subject:* Re: [aprssig] unusual Terrestrial APRS propagation





On Mon, Aug 31, 2015 at 6:38 PM, Paul Bramscher via aprssig <
aprssig at tapr.org> wrote:

No errors in reasoning.  I indeed heard 2m "DX" (Kansas and elsewhere to
Minnesota) -- but ONLY on 144.390 Mhz.  If 2m was genuinely open to
tropo ducting, etc. it wouldn't manifest solely on that freq.  This was
in the daytime over the weekend.  If I truly had a 300-400 mile range on
2m, broadly speaking, there would have been many distant phone
conversations elsewhere on 2m.  Instead, there were none at all.

Likely someone was just re-TX'ing internet traffic locally.



Hi Paul

It is common for people to trust only their own observation.  In this case,
the lack of distant phone conversations on other frequencies is likely
because there were no phone conversations taking place at the instant that
you scanned for them.



What is being observed here is a classic tropospheric anomaly that occurs
when a high pressure system sets up on the East Coast USA.  The phenomenon
has been documented and observed for decades.  In fact, when it occurs over
the Western Atlantic, it is referred to as a "Bermuda High" and hams that
are East of the Appalachian Mountains benefit from it nicely.



The use of RF that is "always on" (APRS, WX Radar, etc) allows for easier
visualization of the event.



I've attached three graphics to illustrate.  They were just captured a
moment ago and are...



Untitled00 = 144-MHz APRS-based propagation maps

Untitled01 = 9-GHz NWS Radar propagation maps

Untitled03 = NWS surface maps



The "geometry" of the inversion layer determines what frequencies it will
affect.



By the way...see that "green patch" in the NWS map?  That indicates a
MASSIVE inversion in progress.  If you were to scan for 10 GHz ham signals,
you'd hear "ssssssssssssss" only because I doubt there are any QSO's taking
place. :-)



'hope this is helpful.



Kind regards,

Ev, W2EV
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