[600MRG] Em Con with 630m - Mountain "propagation"

Mon Jan 6 12:14:44 CST 2014

Gents: You might consider the phenomenon of what is sometimes called, 
"knife edging" of propagation. 

I remember reading a study on this wherein the signal levels at certain 
distances from the tops of mountains or ridges were very significantly 
stronger than both closer-to and further-from those "edges", and that there 
were "zones" wherein this phenomenon was repeated.

As I remember it, the signals were refracted downward at various angles 
due to the edge of the obstruction, somewhat the way light is refracted by a 
sharp edge.

This may explain otherwise difficult-to-explain results.

Further testing is necessary.

Ken W7EKB

On 6 Jan 2014 at 9:06, Edward R Cole wrote:

> Mike,
> 
> That is interesting to know.  The front range is very high reaching
> 14K peaks so would not expect good signal levels the other side.  The
> Kenai Peninsula is rolling hills and lakes similar to parts of
> Minnesota with about 15mi over water to Anchorage then a basin in the
> mountains so not too much obstruction on the path we tested.  About
> 12mi beyond Wasilla are the Talkeetna Mountains which are in the 4-6K
> range.  The Eastern half of the Kenai Peninsula is covered with 4K
> mountains which block VHF path to Seward where one hospital is
> located.  Homer hospital is on the south side of a 1.1K ridge so
> similarly has no VHF path though a 2m repeater is located on the ridge
> which is in range of me at 90mi.  South of Homer is a bay and then
> high mountains.  The Soldotna Hospital and KPB 911 call center are
> 22mi south of me, so closer to the other two sites.
> 
> I would expect fair coverage for 600m to Homer but wonder how it would
> reach to Seward about 120mi thru mountains and valleys.  Occasionally
> we hear the Seward 2m repeater, but this is VHF prop which would be
> totally different.
> 
> Normally I get night-time 80m coverage out 400 to 800 mi. which 
> covers a lot of Alaska.  SE AK is hardest to reach at 800+ miles,
> though very easy on 6m meteor scatter.
> 
> For emcomm the officials want comms on the Peninsula and then links to
> Anchorage 80mi north of the 911call center (which is co-location of
> the Kenai Bureau Emergency Response Center).  Our local ham club holds
> meetings and its annual hamfest in that building.  It would take a
> world-class earthquake to affect all of Alaska infrastructure.  But
> the communications industry now have mobile earth stations to support
> long-distance phone/internet.  250 villages in AK are provided routine
> phone/internet/TV via satellite link using local earth stations.  That
> makes the AK communications system much more endurable to what mother
> nature dishes out.  I believe two undersea phone lines connect us to
> lower-48 plus satellite links.  Those lines were disrupted in the 1964
> event.  The AK RR tracks out of Anchorage to Seward were destroyed and
> took months to restore train traffic.  Seward was nearly destroyed as
> a town since it was hit by Tsunami.  it is the southern RR terminus
> and ice-free port of much shipping.  Tracks go thru Anchorage which
> was created by the RR in 1915 to serve Fairbanks 750mi further north. 
> This is the only RR in state with no connection out of state.  Most
> freight is brought by barge from Seattle.
> 
> Major volcanic eruption, extreme wind storms, and wildfire are other
> potential disasters.  I have seen three eruptions since living up here
> 35 years and many earthquakes.  Fortunately no nearby fires as we are
> in the forest.  Have seen lots of wind over 65mph.  Anchorage hillside
> is subject to 50-100 mph winds several times per year.  So emcomm
> prepareness is important up here.
> 
> OK enough of this, thanks for reading.
> 
> 73, Ed - KL7UW
> 
> At 04:39 AM 1/6/2014, Michael Mussler wrote:
> >My son and I did some 600m tests a few years ago running about 1 w
> >ERP using PSK31 and a mobile 600m receiver. We found that in very
> >rugged terrain (i.e. steep, narrow valleys and canyons here in the
> >Front Range foothills of Colorado) we got solid copy out to 10 miles
> >from the transmitter site. The receive set up consisted of a ferrite
> >rod loop antenna with preamp driving the 630m receiver and laptop
> >computer. We even copied the PSK31 signals with the loop antenna
> >resting on the dashboard inside the vehicle.
> >
> >Consider the utility of a one way communication system during an
> >emergency such as a forest fire or other natural disasters:
> >transmissions of low data rate information (localized WX info, road
> >closures, situation status) could be made to field teams that would
> >not be possible with VHF/UHF repeaters and cell sites that were down.
> >
> >Due to the improved S/N with the WSPR modes, even better coverage
> >should be possible for this application.
> >
> >-Mike Mussler
> >WD2XSH/12
> >AI8Z
> >
> >
> >
> 
> 73, Ed - KL7UW
> http://www.kl7uw.com
>      "Kits made by KL7UW"
> Dubus Mag business:
>      dubususa at gmail.com
> 
> 
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Kenneth G. Gordon W7EKB

"Courage is being scared to death but saddling up anyway."--- John   
Wayne