I'm not an engineer, or antenna designer...just a contester and kind of an
"appliance op".
Back in Florida, I used antenna stacking programs and did not concern myself
with HFTA since most of Florida is pretty much like a table. When I moved
to KH6, it was a different world. On my three acres there is a drop of almost
150 feet, the vertical drop over the next 3500 feet to the ocean is over 800
feet. There are big gulches that drop 500 feet within 300 feet of the
antenna. In another direction it is almost flat for 1000 feet. You get the
idea....HFTA was a must.
I modeled the current set up using the HFTA program by N6BV which is in the
ARRL Antenna Handbook. The set up is on a 150 foot tower and has a stack of
3 tribanders at 92, 56, 29 and two 4 el 40 meter Yagis at 150/80...all
heights modeled from Dean's program. I could have put the tribanders at
greater
heights if I wanted, but I didn't. In the 18 months I've used the stack
designed from that HFTA, I've won lots of contests and even set some records.
The
program works. Just using your intuition may or may not result in a killer
antenna set up. This program gives you a better chance in accomplishing that
killer system.
I'm weak where the program said I was weak...to the south looking up 13500
foot Mauna Kea volcano and to VK/ZL which also goes up hill.. And, I'm a
beacon into EU, which is just what the program predicted if I used the graphs
correctly.
If you're on flat ground don't waste your time with the program, but if you
are on a hilly terrain it's priceless. I don't intend to move my antennas to
different heights to check my results. They might work better at different
heights, but I don't really want to invest the time to find out.
Something to note though...As Dean states, the gain from stacking antennas
tends to get a little sticky when the antennas in the stack start to get below
1/2 wavelength in spacing, giving higher than normally expected gain. Aside
from this caveat, which is just common sense, this program is 10 out of 10.
Once you have your terrain tables the program is easy to use. Be sure to
look at the arrival angles when using the program and focus on the fig. of
merit. No height will be perfect but you'll be able to pick the best one for
overall use.
73 Bill KH7XS/K4XS
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