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From: Ian Walker
Subject: Re: How to check for a 50 or 75 ohm connector
Date: Sun, 22 Dec 2002 08:22:24 +0000
NNTP-Posting-Date: Sun, 22 Dec 2002 09:00:52 +0000 (UTC)
User-Agent: Turnpike/6.02-U ()
In article <3E053579.AFE0BFDF@sympatico.ca>, Dave Holford
>Chris Carlen wrote:
>> George Shaw wrote:
>> > I have a large box of mixed BNC connectors/tees etc.
>> > Using the simplest equipment possible (multimeter?) HOW do I check if
>> > the connector is for 50 Ohm or 75 Ohm coax connection. There are no
>> > external markings.
>> 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.
>Although I have never noticed any obvious difference in the dimension of
>BNC connectors, other than the cable size, I have always understood that
>the difference between the 50 and 75 Ohm "N" connectors was the pin size
>and that attempting to interconnect them could result in damage to the
>connector if attempting to insert a large pin, I forget which was which,
>into a small diameter socket.
It is an urban myth that the centre pins of 50 and75 ohm BNC connectors
are different diameters, probably brought about by an optical illusion
caused by the taper of the pin along with the knowledge that the inner
to outer ratio must be greater for higher impedances. This overlooks
that using a different dielectric will change the impedance, i.e. more
air as in the case of 75 ohm BNC connectors.
>If the connectors are made to either standard I would certainly expect
>them to have a code stamped on somewhere which would identify which one
>they are. If they are not identified then I would doubt that they meet
They do not have to be stamped, although reputable manufactures will
generally want to put their name and part number on them (OEM not
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