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...
References: <3E053579.AFE0BFDF@sympatico.ca> <3keudKjAZXB+Ewcs@newbrain.demon.co.uk>
X-Newsreader: Forte Agent 1.91/32.564
Date: Sun, 22 Dec 2002 11:27:50 GMT
NNTP-Posting-Date: Sun, 22 Dec 2002 06:27:50 EST
On Sun, 22 Dec 2002 08:22:24 +0000, Ian Walker Gave
>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.
Well, it isn't "air". Coaxial cabling usually incorporates a
polyvinyl foam or teflon or other insulator as the dielectric sheath
over the center wire. ALL BNC pin diameters are the same. The
difference is that connectors are made to fit their rear ends into
different cable shapes. THAT is where they differ. The plug side is
always the same.
>>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
Some show the cable type they are meant to have attached to them. I
believe all should, but the world is not perfect... yet.
>If they are not identified then I would doubt that they meet
You can buy movies right after they hit the theaters in China as
>They do not have to be stamped, although reputable manufactures will
>generally want to put their name and part number on them (OEM not
Most folks that work with them on a daily basis can tell by
examination of the rear, cable insertion end of the device in
question. RG-58, RG-59, RG-62, RG-6, RG-174... etc. ALL have BNC
iterations, and all are different sizes. Hell, RG-174 is like an
eighth inch in diameter.