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Re: [TowerTalk] Beverage Layout Problem

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Beverage Layout Problem
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Fri, 16 May 2014 22:28:17 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 5/13/2014 9:18 AM, David Gilbert wrote:
Can you come up with a scientific explanation for why lossy coax picks up more noise than does a lower loss coax?

Coax with a poor shield can convert common mode shield current to differential voltage between center and shield. The standard measure of this is the Transfer Impedance of the shield, and the lower limit on the transfer impedance is the resistance of the shield at the frequency of interest. Many so-called RG6 and RG8-X cables have thin, poorly manufactured shields, so their transfer impedance is high. The higher the transfer impedance, the greater the transfer of noise. Another factor increasing transfer impedance is poor uniformity of the shield.

That's why a good RG58 with a copper braid shield makes a reasonably good coax for Beverages. It's also why it's a good idea to add a common mode choke to that coax.

73, Jim K9YC



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