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Re: Topband: Beverage Feed Line Choke Installation

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Subject: Re: Topband: Beverage Feed Line Choke Installation
From: "Guy Olinger, K2AV" <>
Date: Mon, 1 Jun 2009 21:39:05 -0400
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Many 160m receiving antennas have to assign the ground at the antenna feed 
to the antenna to supply the current sink for the received signal on the 
antenna.  Certainly a beverage or BOG fits this description, as do others. 
The common placement of the transformer I have seen for these types is at 
the signal acceptance end of the antenna.

 If the shack side feedline is also grounded "sufficiently" near the antenna 
feed, then the natural resistance of ground becomes a common path to 
transfer feedline common mode to the antenna on the far side of the 

For these kind of RX antennas, the antenna end of the shackside feedline 
shield needs to be isolated from *both* ground *and* the antenna side of the 
transformer. Several devices for this isolation have already been posted in 
this thread. A common mode choke on the shackside feedline 1/4 wave from the 
transformer toward the shack will attenuate the tendency of a high Z 
isolation at the transformer to form a common mode current node at that 1/4 
wave point and make the shield less liable to accumulate noise current at 
the operating frequency, further restricting common mode signal pickup.

This amounts to *two* common mode chokes though they may be implemented 
quite differently.

Ground on the shackside shield should be somewhere on the shack side of 
*both* chokes.

73, Guy. 

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