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 tochanging 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_________________ Topband Reflector
_________________ Topband Reflector
