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Re: [TenTec] 75 Ohm twin velocity factor ?

To: tentec@contesting.com
Subject: Re: [TenTec] 75 Ohm twin velocity factor ?
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Reply-to: geraldj@storm.weather.net,Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sat, 27 Jan 2007 11:07:37 -0600
List-post: <mailto:tentec@contesting.com>
On Sat, 2007-01-27 at 07:39 -0600, GARY HUBER wrote:
> Common "lamp cord" (parallel conductors), has been used as twin lead and has 
> an impedance of "about" 72 Ohms depending on the exact conductor diameter / 
> spacing / dielectric rating of the insulation.
> 
> Best regards,
> Gary - AB9M
> CSM(r) G.L.Huber
> 9679 Heron Bay Road
> Bloomington, Illinois 61704
> (309)662-0604

Generally the dielectric material in lamp cord is significantly more
lossy at RF than real transmission lines. In the early days of ham use
of transmission lines I've read that twisted rubber and cloth insulated
line cord was used for some feed lines, but it was noticeably lossy at
80 meters. The modern plastics are better but not really great yet.
There was an article in QST about using zip cord a couple years ago.

73, Jerry, K0CQ

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