[TowerTalk] Cost effective Tower height

[K1TTT]

That's what stacks are for!

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net

-----Original Message-----
From: Jim Thomson [mailto:jim.thom at telus.net] 
Sent: Friday, December 02, 2011 14:12
To: towertalk at contesting.com
Subject: [TowerTalk] Cost effective Tower height

Date: Thu, 01 Dec 2011 19:16:14 +0000
From: Steve Hunt <steve at karinya.net>
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.

73,
Steve G3TXQ

##  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 eu,
but not asia, or south pacific.    A lot of times the station with the 50'
high  tribander
would clean the other fellow's clock.   That happened quite often.   I came
along, with
my 20m yagi at 72'..and the 15m yagi 8' higher.  95% of the time I was as
loud as the 100' tall yagi....and  at no time did the 50' tall  tribander
beat me out.  I trounced the
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 time, the angles  were aprx 15 deg.... and that  10 degs  was too
low...and  20 deg was too high. 
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 
20 degs. 

## 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 suggest 80'.
A T-400  trylon  would fit the bill, [ or the AN wireless 80', which is a
lot stronger tower].
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.
Freestanding tower's 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 gauge, etc,
then install 3 x concrete  guy anchor's, you will have saved nothing...or
very little.  

later... Jim  VE7RF

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