BNC connectors - 50 or 75 Ohm ?

[fmunson]

If one thing, I now know I still have soooo much to learn about cables and connectors.

Thanks everyone for the replies (so far - but please keep 'em coming!:)

If it can be of any use, here are the pics of the connectors on the Decklink card and on the HDLink monitoring converter. Cable attached is the one with the connectors shown in the last three pictures in my first post. Everything works fine, all types of video up to and including 2K are shown without glitches on the monitor. The other cable also works fine. That's not to say there isn't a 50/75 mismatch on one or both cables...

Cheers

[Quarlo Klobrigney]

In my too long of experience, video or digital video is always 75 . The connectors make a difference in HDSDI or SDI, as well does the coax.

[edpalmer42]

Oh, for fudge sake!  Those female connectors aren't standard either!

In the picture that fmunson posted above look at the thickness of the center insulator on the female connector.  Now look at the following picture from Wikipedia.  Fmunson's connectors don't match either one.



Maybe they're 62 1/2 ohm connectors.     My head hurts.  

[fmunson]

Now this is interesting...

https://www.eevblog.com/forum/chat/how-to-tell-the-difference-visually-on-bnc-connectors/msg1020633/#msg1020633

This even more (copied from http://www.satcure.co.uk/reviews/satcure_blog_170.htm)

In this month's newsletter (169) you say:

"What always puzzles me about CCTV is that it uses 75 Ohm cable but BNC connectors are 50 Ohm."
- 'fraid not! :-)
BNC connectors are made in 50, 75, and rarely 93 ohm impedances.
I have 50 and 75 ohm examples, and I was going to send a photo showing the difference, but as this is a form rather than an actual email I can't, but you can see it here:

http://www.hibernaculum.org.uk/Secret/Radio/bnc_50-75ohm.jpg

The 50 ohm plug and socket are on the left, the 75 ohm on the right.
The differences are subtle - the 75 ohm version has a slightly wider centre pin and a slightly narrower centre insulator, by about a quarter of a millimetre as far as I can measure them.
Some 75 ohm sockets I have omit the teflon insulator surrounding the "socket pin" and it stands up from the back of the mating chamber on its own - I have no idea why they'd do that.
Just thought you'd like to know - (...)

[edpalmer42]

This just shows how much confusion there is on this topic.  The Wikipedia pictures agree with most of the connectors I've seen, both on cables and equipment, so, until somebody shows me proof to the contrary, that's what I use.

Until someone puts these things on a VNA, we're all just throwing up more confusion.  I suspect that the VNA tests will show that most of the differences are trivial, but a few are significant if you're running very high frequencies and/or very sensitive measurements.  Remember that BNC connectors aren't really suited to either of those situations.  SMA, N, or maybe even TNC are better.

[Martin.M]

to be extendet:

BNC plugs for RG62 = 93 Ohms 

greetings
Martin