[TowerTalk] Cost effective Tower height

[Jim Thomson]

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