From: Alun Palmer
Subject: Re: How to check for a 50 or 75 ohm connector
Date: 22 Dec 2002 21:05:18 GMT
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Don Pearce wrote in
> On Sun, 22 Dec 2002 15:58:24 +0000, John Woodgate
>>I read in sci.electronics.design that Don Pearce
>>wrote (in <firstname.lastname@example.org>) about 'How to
>>check for a 50 or 75 ohm connector', on Sun, 22 Dec 2002:
>>>OK, I have just looked up the technical spec for BNC plugs, and the
>>>pin diameter for BOTH 50 and 75 ohm devices is given as 1.32 to 1.37
>>What 'technical specs'?
> I looked here - grab the pfd's for 50 and 75, compare and contrast.
> Telecommunications consultant
The centre pins on 75 Ohm BNC plugs are very slightly larger, so that
inserting them in a 50 Ohm BNC socket causes damage by enlarging the hole.
I used to work in a lab where we had both.
I'm not sure how F connectors got into this thread, but they are nasty
rubbish, worse even than Belling-Lee connectors. Only use F connectors if
you absolutely have to. They make UHF connectors look like an engineering
masterpiece by comparison, which they're not.
F connectors leak RF in and out like a sieve. One of my old colleagues did
extensive tests of 'transfer impedance' (this has nothing to do with
characteristic impedance, but is a measure of screening) and could find
nothing under the sun that had worse screening than an F connector.