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Re: [TowerTalk] phasing antennas

To: towertalk@contesting.com
Subject: Re: [TowerTalk] phasing antennas
From: K4SB <k4sb@bellsouth.net>
Date: Tue, 15 Mar 2005 05:10:50 +0000
List-post: <mailto:towertalk@contesting.com>
Jim Lux wrote:
> If one has a good antenna analyzer that reads both R and X, and you collect
> enough frequency points, you can calculate what a TDR would have given you.
> The Fourier transform is used to convert back and forth between time domain
> and frequency domain.
> 
> Looking  for dips in frequency domain is essentially a special case of this
> duality.  You're looking for places where the time delay for an impulse to
> propagate from one end to the other happens to be an exact multiple of one
> RF period.
----------

Good advice. Just a little addition. If you use an analyzer, use as
high a multiple of the frequency you want as possible. For example,
the MFJ is good to 170 mHz. For 50.1 or so, you'll get a much sharper
dip around 150 +.

And for heavens sake, always use a length of coax which is long enough
for both phasing lines. Velocity Factors vary widely, but rarely are
not the same in any one run of coax.

73
Ed
_______________________________________________

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Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
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