Date: Thu, 01 Dec 2011 19:16:14 +0000
From: Steve Hunt <email@example.com>
Subject: Re: [TowerTalk] Cost effectivel Tower height
I think we sometimes concentrate too much on looking at antenna heights
that will maximize gain at certain take-off angles, and forget about the
nulls. Those deep elevation nulls can be "killers" if arrival angles
over a wanted path happen to fall in them.
So, before going firm on a height I'd encourage you to look at the ARRL
Angle-of-Arrival statistics for various bands and paths, and make sure
your selected height is not going to put a deep null at a high
probability arrival angle for the bands/paths you are most interested
in. It might be a better trade to be 1dB weak for 80% of the time rather
than 20dB weak for 20% of the time, if you get my point.
## I'd agree on this. For a single height, I'd opt for 70-85' range.
70' is a winner every time for a single height, for a multiband 40-10m
yagi that you propose. Back in the late 1970's here in town, we had one
fellow with his tribander at 50'..... and another fellow with 20 m monobander
at 100'...[ and with a 10/15 m interlaced array, 10' above the 20m yagi].
## The fellow with the 100' tall yagi would win out 85% of the time for dx to
but not asia, or south pacific. A lot of times the station with the 50'
would clean the other fellow's clock. That happened quite often. I came
my 20m yagi at 72'..and the 15m yagi 8' higher. 95% of the time I was as loud
100' tall yagi....and at no time did the 50' tall tribander beat me out. I
50' tall array, hands down, any direction, any time of the day.
## after 2 years of this back and forth testing, my conclusion was most of the
angles were aprx 15 deg.... and that 10 degs was too low...and 20 deg was
To make matter's worse.... the fellow with the 100' high ant [10 deg angle]
had a perfect
NULL at 20 degs ! And of course the fellow with the 50' high tribander
had max gain at
## Higher is better..up to a point, then you get too high, and then u have
diminishing returns, PLUS
you now have a big null at 20 degs. Of course if you have a motorized crank
up, you can have
your cake and eat it too. Since your proposed array is a 40-10m affair, I'd
A T-400 trylon would fit the bill, [ or the AN wireless 80', which is a lot
Don't go cheap on the rotor, it's a one shot deal, PST-61, OR-2800, something
big, with loads
of TQ. Use anything smaller, and you will trash it, then you will have to
replace with a big rotor
anyway, so you saved...nothing.
## OK, you have neg 5 deg slope in all directions. I'd opt for 70' then.
Like a T-500 trylon,
or the 70' an wireless. Don't go cheap on the tower either..u want the WIDE
base. If using the
trylon, make it 6' deep, instead of 5 1/2'..and use a grid of re-bar across
the top, so u have re-bar on
5 x sides..and use 30 mpa concrete [ 4350 psi..or at least 4000 psi]. The
tower and the base is
another one shot deal. In a 70+ mph wind + ice, then you can sleep at night.
are a lot easier to deal with when installing any yagi..and no guys to mess
with. By the time you
buy the megabuck phillystran and the rohn 45, guy brackets, turnbuckles, loos
then install 3 x concrete guy anchor's, you will have saved nothing...or very
later... Jim VE7RF
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