[aprssig] unusual Terrestrial APRS propagation

Stephen H. Smith wa8lmf2 at aol.com
Mon Aug 31 14:49:47 CDT 2015

On 8/31/2015 7:39 AM, Nagi Punyamurthula via aprssig wrote:
> I have been monitoring the VHF APRS propagation
> <http://aprs.mountainlake.k12.mn.us/> map the last few days and have been
> noticing an unusually long range propagation.  Very rarely does my APRS sysop
> station hear others beyond the MN, IA, SD, ND, KS, WI, IL states – even w/ some
> previously experienced solar flares/storms. Anyone has any hints on what might
> be causing this out of norm propagation.
> I was monitoring http://SolarHam.com/ for some info and found this from 2 days ago.
> Thanks

It's nearly impossible to say, since there is no explanation of how this map 
was generated or what it is supposed to mean.   The URL you cited produces a 
Google Maps mashup with absolutely no explanation.   Is this:

- Off-the-air RX in MN?

- Internet feed looking at original station location and igate location?

- Or what????

What is the color-coded legend coding large blob areas in miles supposed to 
mean? Presumably a number of stations at varying distances were heard

It is extraordinarily unlikely that solar conditions would affect propagation 
on VHF, outside of possible auroral effects during a solar storm.     In turn, 
auroral propagation would be very unlikely to do anything for APRS, since it 
normally yields very distorted rapidly-changing and fading signals that would 
be fatal to packet data bursts.  Auroral propagation is normally only usable on 
CW or sometimes SSB.

Most likely it's tropospheric propagation and ducting which happens during 
rapid day-->night-->day temperature and humidity changes in the lower 
atmosphere.  These two-meter "band openings" happen most commonly during the 
spring and fall "shoulder seasons" in the upper midwest when the day vs night 
temp swings are the greatest.

Note that the last week or so, the usual late summer heat and muggyness was 
abruptly replaced by a more autumnal weather system for several days before 
returning to the usual weather for this time of year.



Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

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