John Passaneau wrote:
On 6/5/2010 5:49 PM, Geoffrey S. Mendelson wrote:

1. Can I connect a 75ohm BNC plug (which is a different size) to a
50oHm BNC socket?

No the size of the center conductor pin is different between 75 and 50
ohm connectors and will either make bad contact or damage the socket.

That's not necessarily true. I have some RG-59 cables with male 75 ohm
BNC connectors that mate fine with 50 ohm connectors. The diameter of
the 75 ohm connector center pin is the same diameter as 50 ohm
connectors. The difference is that the dielectric surrounding the center
pin of the 75 ohm connector is much thinner. And at the point where the
pin enters the solid dielectric at the bottom, the 75 ohm pin doesn't
step up in diameter.

Others have said that there are some 75 ohm BNC connectors which won't
interconnect without damage. But I do know there are some that mate with
no problem. 50 ohm BNC connectors and adapters are very common. I
suggest you get one and compare the center pin diameter with that of
your 75 ohm connector. If it's the same, the two can interconnect
without damage.

I also have a lot of RG-59 cables with 50 ohm BNC connectors. That's
probably more common, since 50 ohm connectors are much more common, and
the connector choice won't make any practical difference in the vast
majority of applications.

Roy Lewallen, W7EL