[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.
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
EchoLink: Node # 14400 [Think bottom of the 2-meter band]
Home Page: http://wa8lmf.net
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