[TowerTalk] Not just what antenna, but how high and the QTH
w9ac at arrl.net
Sun Apr 12 23:40:20 EDT 2015
> "Mike brings up an interesting point. Yes, the antenna is important, but
so is how high you put it up and the surrounding terrain. I can't stress
strongly enough how important it is to do HFTA, especially if you live on
anything other than flat Florida terrain."
Even Florida has some siting opportunities that make HFTA worthwhile. As
K4XS, mentioned, using HFTA over long periods of time will make easier
siting decisions. The sites I have researched are either on geographic
"knobs," like the W3CRA site in Canonsburg, PA, or sites along a river that
meander in an arc toward the most desired directions. Those sites often
provide a moderate drop over a large azimuth arc, and that's what creates
low, controlled take-off angles below 5 degrees.
The site we're finishing this month is located to the east and south of the
St. Mary's River near Hilliard, FL. By the HFTA computations, there's no
viable height that can take the place of the sloping geography. For
example, into Oceana and JA on 40m, we would need to be more than 220 ft.
above ground to equal 1-3 degree TOA performance at 140 ft over sloping
terrain, looking to the west and north. Sounds easy, but it isn’t. It
takes a lot of patience to find the right geography that works for a
neighborhood installation or even an internet remote location. Last year, I
spent countless hours looking for remote sites with these geographic
features that had access to AC power and high speed internet. The list
gets whittled down very fast.
One of the most interesting areas I've researched is Charleston, WV. There
are many locations in residential neighborhoods that offer superb geography
for low TOA from antennas that need only be up 40 ft or less and at very low
angles, will be competitive with tall stacks over flat terrain. One example
of this is the former site of Al Hix, W8AH. One motorized tower to optimize
height per band, and you're done -- at least if long-haul DX is your thing.
There is one piece of property on a city lot at the end of a high cul-de-sac
that according to HFTA, would produce extraordinary low TOA all the way down
to 80m with low antenna heights in about a 300 degree arc - and do it with a
smooth vertical profile.
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