From: Ian Walker
Subject: Re: How to check for a 50 or 75 ohm connector
Date: Sun, 22 Dec 2002 10:57:58 +0000
NNTP-Posting-Date: Sun, 22 Dec 2002 11:00:45 +0000 (UTC)
User-Agent: Turnpike/6.02-U ()
In article , harrogate
>"Ian Walker" wrote in message
>> In article , Don Pearce
>> >On Sat, 21 Dec 2002 22:13:43 +0000, George Shaw
>> >>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.
>> >Look inside the end of the connector. The 75 ohm will have the pin,
>> >surrounded by just the slotted metal sleeve. On the 50 ohm connector,
>> >the metal sleeve will have a layer of plastic insulation just inside
>> >it, forming a second sleeve.
>> That is almost correct for BNC; except there are two styles of 75 ohm
>> BNC, one as you describe and the other has no insulating sleeve around
>> the female receptacle and thin sleeve around the inside of the outer
>> conductor of the male compared to 50 ohm connector. Both types of 75 ohm
>> and the 50 ohm BNC can be mated non-destructively but the impedance
>> discontinuity could cause problems. The difference with N type is much
>> simpler, the 50 ohm has the same diameters as a BNC, the 75 ohm has a
>> smaller centre pin. The two types can not be mated, a 50 ohm plug
>> inserted into a 75 ohm socket will damage the socket, a 75 ohm plug
>> inserted into a 50 ohm socket will fail to provide a reliable centre
>> connection. The observant will have noticed that you can push a 50 ohm
>> N onto either impedance BNC without harm, although this is not
>> recommended for power or where you need to measure amplitude.
>> Ian G8ILZ
>Also look at the hole in the pin - 75R is significantly smaller that 50R as
>the core is thinner.
With N type that is correct; but for BNC you are wrong, Wrong, WRONG!
How many times must I state the B******g fact!!