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Re: [TowerTalk] Balun question shield leakage

To: Tom Rauch <>,"Jim Brown" <>,"Tower Talk List" <>
Subject: Re: [TowerTalk] Balun question shield leakage
From: Jim Lux <>
Date: Thu, 14 Jun 2007 16:27:38 -0700
List-post: <>
At 01:53 PM 6/14/2007, Tom Rauch wrote:
> > Anything is possible, of course, but coax would have to be
> > pretty awful for
> > enough field from the differential signal to cause
> > significant heating.
>"Unlikely" isn't strong enough, it would be impossible.
>I can buy the cheapest radio shack coax, the type that you
>can see through the shield to the center dielectric, and it
>is nearly impossible to measure the leakage through that
>shield unless I use special equipment.

>Let's not obsess about things that don't mean anything. Let
>the Audio-phools and CBers worry about those shields.

I suspect that a crummy shield would have a larger effect on IR 
losses than on anything else.  But, since the surface area of the 
shield is so much larger than the center conductor, I would think 
that the center conductor dominates. For foamed dielectric, I think 
75 ohm cable is around 5:1 diameter ratio, so the shield only 
contributes 15-20% of the loss.  For 50 ohm cable, the ratio is 
smaller, so the shield loss would be more important. 


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