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Re: [TowerTalk] CMC-230-5K

To: towertalk@contesting.com
Subject: Re: [TowerTalk] CMC-230-5K
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Thu, 21 Apr 2016 11:31:33 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On Thu,4/21/2016 11:12 AM, Tod wrote:
As a matter of curiosity:

You have a (CMC) Common Mode Choke in a feed line.  You add another, identical, 
choke in line.

If the first choke attenuates the common mode current by 20 dB, the what is the 
total attenuation after you add the second Choke?

That depends on how the two chokes affect common mode voltage and current as a result of their placement, and there is no short answer. First, the attenuation of a single choke depends entirely on the common mode circuit into which it is inserted, and that circuit varies widely with frequency for any given system. The variables include the imbalance of the antenna, the electrical length of the feedline, the termination of the feedline at the transmitter, the routing of the feedline from the antenna, etc. A really good choke could provide as little as a few dB or as much as 20 dB, depending on those variables. 20dB is a LOT of attenuation, and a very good choke would provide that only if the common mode voltage was quite high. In that situation, a second identical choke in series would increase attenuation by no more than 6 dB.

73, Jim K9YC
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