[TowerTalk] HFTA question
jim at audiosystemsgroup.com
Thu Jan 21 08:42:45 PST 2010
On Thu, 21 Jan 2010 11:12:52 EST, cqtestk4xs at aol.com wrote:
>One additional piece of info. The further away the terrain the less of an
>effect it will have. N6BV was kind enough to run some numbers for me and
>the numbers for the terrain were computed up to around 14000 ft. He told
>me there was no reason to go to any further than that.
Yes. N6BV is a member of our contest club, and he's advised many of us
individually about this. I live in rather mountainous terrain, and he advised
me to use the most detailed maps and go out to that 14,000 ft distance.
K6XX is my neighbor, and both of us have used HFTA extensively in planning our
antenna farms. Bob is near the top of a 2,700 ft ridge, I'm at 2,000 ft on the
west side. For both of us, terrain near the limits of that 14,000 ft data set
has significant effect on our propagation.
As to stacks -- as I understand it, HFTA is NOT designed to predict stacking
gain, but rather to evaluate the effects of antennas at multiple heights in a
stack. It is designed ONLY to predict the interaction of a horizontally
polarized wavefront with terrain. Nothing more. Antenna directivity is NOT in
the program. When you select a dipole or one of the Yagis, you simply raising
the signal level by the forward gain of a typical antenna of that generic
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