The center pin for 50 Ohm and 75 Ohm BNC are the same. The difference in impedance is determine by the dielectric. If you look at a 50 Ohm BNC connector you see dielectric around the center pin for the female and around the inside perimeter for the male. The 75 Ohm BNC is missing this dielectric.

It is very easy to see the difference if you know what to look for.

The Type N connector impedance is determined by the diameter of the center pin. The 75 Ohm connector had a smaller diameter center pin than does the 50 Ohm connector. To insert a 50 Ohm male Type N connector into a 75 Ohm female will destroy the female center pin. To insert a 75 Ohm male type N connector into a 50 Ohm male may not do any damage, but the connection will be very unreliable.

73 Glenn WB4UIV Retired TV Chief Engineer

On 7/25/2020 6:15 PM, GEO Badger via AMSAT-BB wrote:

Same with the 75??? BNC/M connector.

Ciao baby, catch you on the flip side 73 de W3AB/GEO

http://www.w3ab.org

You can say "over", you can say "out", you just can't say "over and out".

 On Saturday, July 25, 2020, 11:52:48 AM PDT, Zach Metzinger via AMSAT-BB <amsat-bb@amsat.org> wrote:

I just ran across this tidbit[1]:

...

Q: How can I tell the difference between a 50 and 75 Ohm N connector? A: You can tell the difference by the center pin. A 50 Ohm connector has a pointed pin. A 75 Ohm has a rounded pin.

I've always looked at the center conductor to shield (not ferrule) distance to make sure I had a 50-ohm version. I don't have any 75-ohm versions lying about the shack. Can anyone else confirm this?

I recall, back in my RF engineer days, that we had a whole box of 75-ohm N connectors which were marked with bright red paint. Woe to the junior engineer who coupled the 50-ohm and 75-ohm version, which would bend the center spring fingers on the female connector apart permanently.

One can also kill a female N connector by mating it with a male PL-259. I have not done this myself, but I knew someone who did this twice on his fancy new antenna analyzer and wondering why everything was such a poor match. :-)

[1] https://www.showmecables.com/n-male-crimp-connector-lmr-400-belden-9913

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Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb