Hi Guys,

On Thu, 1 Jul 2004 14:30:28 +0200, "Helmut"
wrote:

Bernhard,

Please keep in mind, that VHF and UHF do verry much reflect from your
surrounding "masks", and you would not believe what is possible to reach
without line of sight.

Although my situation may not be "Alpine," I do live between two
mountain ranges in hilly country (terrain varies 200M through many
river valleys). To the East are the Cascade Range with more than the
average density of Volcanos (think Mt. St. Helens or Mt. Ranier, or
Mt. Hood, or ,,,) which stand in the 4000M area. However, they are
exceptions to the general rule, because the surrounding Cascades are
rather smaller at maybe half to 2/3rds those big guns.

To the west we have the Olympic Mountain Range which are on par with
the Cascades for height. Living between them, my friend often find
they can get better contacts by aiming their beams 180° to their
target because there is a small hill in the way and the reflections
off the mountains behind give more than enough signal.

There is also the phenomenon of knife edge diffraction that occurs at
these hill's peaks or ridges. Myself, I live behind a hill that
interferes with my buddy's repeater. I live at 100M above sea level
(Puget Sound), the hill rises to 150M and masks the repeater antenna.
I use RadioMobile software to map the geographic distribution of RF:
http://www.qsl.net/aa7uj/
or
http://www.qsl.net/aa7uj/coverage/10m-1uv.jpg
which is one of several footprints, this one being the 1 µV
sensitivity service area (shown in orange) for the 10M repeater.

Now, if the concern is with HF bands, then that is probably more a
concern of DX coverage (not suited to RadioMobile as it is principally
line of sight oriented). There I use VOAWIN which is a gargantuan and
very busy propagation modeler. An example of this is found at:
http://www.qsl.net/kb7qhc/propagation/index.htm

The first pass analysis of how much terrain impacts your signal can be
evaluated by simply looking at the peaks. How many degrees above the
horizontal do they rise? If less than 10° then no big deal. If more
than 50° then you must be living in a cave (most slopes are rarely
steeper than 20-30°). I must say there are exceptions like deep
valleys. Last week I was in the Royal Gorge that is 400M deep and
maybe 100M wide.

73's
Richard Clark, KB7QHC