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Old 6th Oct 2018, 5:56 pm   #13
TonyDuell
Dekatron
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,190
Default Re: Determining Zo for coax cable

I have a very simple TDR (actually a telephone line tester, 'Tester 301B'). I found it quite interesting that if I connected 1000 feet of twisted pair (a full reel of ethernet cable) to it I got the expected reflection. Shorting the free end turned the reflection over (if you see what I mean). And when I connected a resistance box to the free end, the reflection disappeared at 100 ohms or so. Said resistance box was not designed for high frequency work either (but I suspect the resistance coils are non-inductively wound).

Nothing like seeing it in practice (on the little CRT of the Tester 301B) to get it to stick in your mind.
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