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

Mon Jan 6 18:25:14 CST 2014

Ken,

I normally see the term in use as a form of VHF to microwave 
propagation, but I suppose it may exist at longer wavelength though 
maybe will less pronounced effect.  Early in radio history the 4/3 
earth phenomena was discovered which is a slight bending over the 
horizon due to slowing of the wave at the air/ground interface.  I 
would guess this is still operative over mountains, but probably 
leaves a significant "shadow" on the far side.  Comments that the 
signal is again copyable out in following valleys or plains would support that.

I am not an expert on MW propagation but I assume 600m is at the 
point where there is some sky wave under certain circumstances.  That 
is easily seen in BC signals at night.  But is good for our use.

But ham radio has a very different goal than commercial 
communications.  For commercial use what it wanted is predictable and 
reliable radio paths.  Thus the prevalent ground-wave is very useful 
in that application.  Why AM BC are where they are (partly...probably 
historical use and technology played a part).  FM BC is at a 
frequency that has little ionospheric effects but does conform well 
to mountainous terrain for better coverage - same application for VHF 
TV.  Channel-2 is the most desired frequency for range and coverage.

73, Ed

At 09:14 AM 1/6/2014, Kenneth G. Gordon wrote:
>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
>
>
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73, Ed - KL7UW
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