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Re: [TowerTalk] To get a truly balanced antenna feed

To: towertalk@contesting.com
Subject: Re: [TowerTalk] To get a truly balanced antenna feed
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Tue, 28 Jun 2016 09:36:32 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On Fri,6/24/2016 8:16 AM, jimlux wrote:
or that matter, that's why cat 5 has twisted pairs with different twist rates.

Actually, the reason is to minimize crosstalk between pairs by the mechanism that Neil Muncy (W3WJE, SK) called "shield-current-induced noise." He was describing it on shielded twisted pair where the shield was foil plus drain, with the drain twisted at the same rate (lay) as the signal pair, but much closer to one of the pair conductors than the other. That caused shield current to inductively couple more strongly to that conductor than the other, creating a differential voltage in the signal pair. The different twist rates of CAT5 eliminates that by randomizing the coupling.

His paper documenting both this mechanism and The Pin One Problem were presented in Oct 1994, and published in the Journal of the Audio Engineering Society in June 1995. That same issue also includes Bill Whitlock's definitive work on the balanced interface, which caused IEC to later rewrite its Standard on measuring balance in circuits. JAES is in most engineering libraries, and articles can be downloaded from aes.org (but not for free).

73, Jim K9YC

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