[AK-VHF] ak-vhf Digest, Vol 77, Issue 6

[Edward R Cole]

Brandon,

At 07:05 PM 3/16/2018, Brandon Clark wrote:
>Ed and Shannon,
>
>Thus is an interesting thread, and echoes a lot of what I've learned in my
>few years of VHF/UHF radio work. With this kind of work factors you
>wouldn't notice at HF become very significant, such as adding a few more
>elements, getting ten feet hiher up, or adding a few more watts.

VHF and higher propagation modes are very different from operating HF 
where one uses ionospheric prop.  6m is half-way between HF and VHF 
so you get a mix of prop types, including many not used lower on 
HF.  Sporatic-E, Auroral-E, Aurora, meteor scatter.  Troposcatter, 
Knife-edge scattering over mountain ridges are a few.  Airplane 
scatter and Moon bounce, even rain scatter.


>An interesting project would be to get everyone on the Tuesday and Saturday
>nets to log all the contact they can hear, and then list their antenna,
>location, and power on the log sheet. That could then be fed into a Google
>earth map showing station locations as pins on the maps, lines as good
>signal paths, and the color of the lines representing the combined "oomph"
>of the stations (combined antenna gain and Tx power f9rnthe stations in
>contact). After a month or two, and with a few mobile stations to try out
>less used locations, you would have a map of the VHF/UHF signal paths for
>south centrsl alaska. Coukd be handy for emcom and contest planning.

Better yet use new digital modes to test propagation as your 
observations can be sent to internet sites that log all activity and 
give you a display on a map of the paths.  Callsigns, time/date, and 
signal levels are displayed.  WSPR and FT8 have been doing this.  You 
can run automatic beaconing.


>It's also interesting that the subject of propagation keeps coming up. I've
>noticed recurring temperature inversions and low cloud activity since I
>moved here in Dec. I wonder if there may be some waveguide action going on
>in the area. In CA guys would wait for the right weather, drive up to the
>right elevation duringnan inversion, and then been out to Hawaii on VHF
>through the GHz bands, using these specific weather patterns as waveguides.
>Might be happening here too.

There is a persistent inversion layer over Cook Inlet and adjacent 
land areas.  Normally when cold-clear calm wx is present.  Cold air 
is trapped under warmer air which is opposite of normal air temp 
gradients.  Easily noted if you are in an area with wood heating as 
smoked lays over horizontal after rising a ways.  More evident during 
winter months.  Windy wx usually stirs up the atmosphere dispersing 
such layering.

On occasion I have had problems working KL6M or KL4E who are on 
hillsides and apparently on high side of an inversion, whereas I am 
below.  On microwaves actual tunnels will form snaking around which 
can enhance communication if two stations happen to be inside.  Guys 
above 2-GHz see this often.  Also prop may be great at a seashore and 
not on a nearby mountain (or vice versa).

Propagation by bouncing off mountain side is often better than direct 
path (2m and higher bands).  Shot from Anchorage to Fairbanks is nt a 
straight line.  Many use Mt. Denali as a backscatter reflector which 
allows a 120-degree bank shot.  Mountain scatter paths are greatly 
varying and especially affected by snow cover.

With a good directional antenna in the clear one can take advantage 
of many of these phenomena.  But sometimes a good gain vertical will 
work as well or better.  VHF prop is strange and interesting.

73, Ed

>Brandon
>
>PS: Anchorage to Fairbanks at VHF? What bands, how much power, and from
>where? Definitely need to incorporate that possibility into my roving plans.
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73, Ed - KL7UW
   http://www.kl7uw.com
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