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[TowerTalk] Tower height question

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Subject: [TowerTalk] Tower height question
From: (Bill Coleman)
Date: Mon, 8 Oct 2001 19:32:34 -0400
On 9/17/01 12:43 PM, Lawrence, Kirk at wrote:

>Not sure if I have seen this before, but can't seem to find it
>so here goes.  I am planning on putting up a tower, approx. 10-15 feet
>away from my shack (the base is anyway) with a 4 element tri-bander on
>it [Mosley].  My question is, how high must I go to avoid RF from
>overloading inside? I had a tower at a different location that was
>approx. 25 feet high with the same antenna and had quite a bit of RF
>staying in..could have been something else entirely....but I felt it
>may be because I was not high enough. 

It's not clear that the problem you had originally was due to antenna 
proximity. It could be that currents were being carried into the shack on 
the feed or rotator lines, or perhaps from the wiring in the house. You 
don't indicate if you were running any power or not. That could make a 
big difference.

One issue today is that Amatuer stations have to meet standards for RF 
exposure. If you run less than 50 watts on HF, or less than 100 watts 
below 20 MHz, you don't have to worry. But if you run more power than 
this, then you need to do RF exposure calculations. Those calculations 
along might suggest to you how high you need to get the antenna.

> So the question is, what might
>be the minimum I can get away with.  I am considering a 50 ft.

A couple of other things to consider. Were you planning to obtain the 
proper building permits, variances, etc required in your county or city 
of residence. Here in Gwinnett County, GA, building a tower less than 50 
feet is a lot less of a hassle than one greater than 50 feet. That's why 
mine is 49.5 feet tall.

Also, the tribander itself will perform "better" the higher you get it. 
50 feet is a great height for 10m, good for 15m and adequate for 20m. In 
any case, it would be much better than the original 25 feet. So, higher 
is better, so tend to err on the higher side, if you can.

Bill Coleman, AA4LR, PP-ASEL        Mail:
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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