[aprssig] unusual Terrestrial APRS propagation

Ev Tupis w2ev at yahoo.com
Tue Sep 1 08:19:55 CDT 2015


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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