Topband: twisted pair cable

[Bruce]

Wondered why this cable was working well. Of the cables this company is 
selling it appears the only one that has its impedance (55 ohms) posted. I 
decided to cut a section lengthwise to find out if the drain wire was in 
fact was next to the twisted pair and it is not. It runs in a straight line 
on the outside of the foil.
http://www.markertek.com/Cables/Bulk-Wire-Cable/Bulk-Audio-Cable/West-Penn-Wire-Corp/WP-D25291-P.xhtml?WP-D25291-1000

73 Bruce-K1FZ



> It is working well, and possibly because it is buried except a short 
> distance at both ends.  I was avoiding burying a non shielded, twisted 
> pair with possible varying losses due to
> changing ground conditions.
>
> 73
> Bruce-K1FZ
>
>
>
> On 8/12/2013 1:42 PM, Bruce wrote:
> I am using a twisted  pair, with shield,  that is near  55 ohm
> impedance for
> my receiving delta loop. The cable is designed for audio,
>
> Depending on the nature of that cable, you're probably better off
> without the shield if both ends are transformer-isolated as I described.
> There are two potential problems. First, the shield provides a lovely
> path for common mode current, which can couple noise via Pin One
> Problems to a rig. Second, if the cable shield is foil plus drain wire
> ("rack wire" like Belden 8451), shield current will be STRONGLY coupled
> to the twisted pair by a mechanism that Neil Muncy named
> "shield-current-induced noise" (SCIN). The mechanism is that the drain
> wire has the same lay as the signal pair, and is manufactured so that it
> is much closer to one conductor the pair than the other. This results in
> more inductive coupling to the closer conductor, converting the common
> mode current to a differential voltage.
>
> 73, Jim K9YC
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