On Wed, 18 Mar 2009 13:34:36 -0500, K4SAV wrote:
>Take off angle from irregular terrain has even less meaning than it does
>from flat ground. The only thing of significance is the gain at a
>particular angle.
Count me among those who find HFTA to be quite useful in predicting the
relative advantage/disadvantage of various mounting heights for horizontal
antennas based on terrain data AND propagation data. It MUST be remembered
that the propagation data is an average over long periods over a lot of
specific paths, and that there are variations from hour to hour, day to
day, and year to year. It must also be remembered that the prediction will
be only as good as the terrain data you plug into it.
When I moved here (the Santa Cruz Mountains near San Francisco), I took a
visual look at my situation (a ridge to the north and east) and a LOT of
tall trees) and said to myself "higher is better, and you can't get them
too high." The serious hams around here (contesters and DXers) are all
quite hot on HFTA, and the author (N6BV) is a member of our ham club. His
advice, based on my highly irregular terrain, was to use the most detailed
terrain data on line, and carry it out for the greatest practical
distance. I did that, and HFTA pretty well confirmed all of my 54 year old
ham's seat of the pants observations ("higher is better, and I can't get
them too high.")
Over the next year or so, I started with low antennas just to get on the
air, then gradually found ways to get them higher in increments of 10-20
ft at a time. Each time I got them higher, they worked better. Exactly
what HFTA told me. Now all my HF antennas are at 100-110 ft, and they work
very well.
I'm looking forward to seeing Steve Hunt's work, and I'll apply it to my
situation as soon as I have time to do so.
73,
Jim Brown K9YC
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