Quote:
Originally Posted by TonyDuell
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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I was up a ladder at the front of the house, and found I could demonstrate the mechanical equivalent of this to my kids by giving our phone line a big thump and watching the out-of-phase reflection come back from the pole. Well, that dealt with the high-Z termination case. I'll have to creep out at night to the pole and think about how to characteristically terminate it. And the low-Z case will annoy the missus when she wants to use the internet
