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Subject: Re: How to check for a 50 or 75 ohm connector
Summary: What do you think of these ping times eh?
Reply-To: You can't see me, and I pass right through planets...
X-Newsreader: Forte Agent 1.91/32.564
Date: Mon, 23 Dec 2002 04:30:39 GMT
NNTP-Posting-Date: Sun, 22 Dec 2002 23:30:39 EST
On Sun, 22 Dec 2002 22:22:29 -0500, Boris Mohar
> Little do you know. You are pulling this out of your but without any
>direct knowledge or experience. My first intro to the TDR was about
>thirty five years ago when the instructor hooked up one up to a peace of
>cabling that consisted of various lengths that were interconnected with
>various connectors. He proceeded to demonstrate the importance of good
>impedance match between the cable and the connector as each of the splices
>showed up on the TDR. He than pinched a cable slightly and that slight
>deformation showed up also. Every connector represents a impedance
>discontinuity. The whole point is to minimize that. Often you work with
>signals of low enough frequency and cables that are short enough so that
>these things are not obvious but believe me they are there and they
>sometimes matter. I work on ground penetrating radar where we send a 1kV
>2ns rise time pulse to antenna. Any little discontinuity on the line
>shows up as false echo and really messes up the return signal.
>You can make a reasonable TDS out of a fast pulse generator and a decent
>scope. Go convince yourself.
I have an HP spectrum analyzer at work. I'll fashion some cables up
with improper parts, and see what frequency it starts to matter at.
I'd bet it to be quite small, all the way up until GHz levels.
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