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[TowerTalk] feeding a Rohn45 rotating tower.

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Subject: [TowerTalk] feeding a Rohn45 rotating tower.
From: (Tom Rauch)
Date: Fri, 6 Aug 1999 21:04:45 -0400

> but nothing seems to make any difference.  I have connected to the shunt
> wire direct and through an 800pf cap.. Most likely I just don't know what
> I'm looking for!! Any hints rather than "GIVE IT UP".


The resistance meter of the 259 is somewhat misleading. It is 
resistance only at resonance, and you probably can't get there with 
a tower that tall. the reason is the tower is already low in 
frequency, and the beam makes it lower. The series inductance of 
the gamma wire makes it lower yet, especially if the gamma wire is 
thin compared to the tower.

If it was my tower, I'd borrow a 259B or some other analyzer that 
reads true R. If you are close to any BC stations, it might screw 
that reading up so I'd use the tunable filter MFJ sells or make one 
of my own out of a parallel L/C network with very high C and small 

>From that point, you'll be able to see what is going on.

My bet is with the tower height and antenna you have, the gamma 
wire will be pretty long and 500 pF will be way too much C with a 
gamma wire and not a cage. You could use an omega match, but 
it will have less bandwidth than the proper tap point and a single 
capacitor. It would be easier to adjust.

I think ON4UN's book has some good starting points.

73, Tom W8JI

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