From: John Woodgate
Subject: Re: How to check for a 50 or 75 ohm connector
Date: Sun, 22 Dec 2002 08:02:06 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Sun, 22 Dec 2002 10:31:55 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Chris Carlen
wrote (in ) about 'How to check for a 50 or 75 ohm connector',
on Sun, 22 Dec 2002:
>I find it very difficult to accept the suggestions that 50R vs. 75R
>connectors have different diameter pins, as that would imply that the
>"BNC" connector has different mechanical standards for different
>impedances. If this is truly the case, then I will be eager to learn
>that it is so.
It IS so. It's basically the ratio of pin diameter to sleeve diameter
that determines the characteristic impedance. The required ratio is
affected by the presence of insulating material.
>But until I'm convinced, I would hesitate to make any certain judgements
>about the connector impedances.
Well, it can be proved mathematically that what I say above is true, but
I can't reproduce the proof here. Try a textbook.
> Also, the appearance or presence of an
>insulating material is of little value in determining the impedance as well.
By increasing the capacitance between inner and outer, insulating
material tends to lower the characteristic impedance.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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