BNC Connectors

It is the inner ring which provides the continuous 50 ohm impedance; the outer ring is merely for mechanical locking.

BNC = Bayonet Neill Concelman.

Also, the thread in TNC is als only for mechanical locking - Threaded Neill-Concelman.

The only 'butt' connection connectors I've see were the APC [about the size of type N] out of HP [those solid 'swing arms on their Network Analyzer] The connector were 'sexless' and center pin was butted against the oposite connector's center pin. Tony Badger designed it at HP and the connector was good up to a whopping 22GHz at the time.

Thanks for the exact name reference for BNC. Back in the day there were BNC terminated RG-58, 50 ohm cabling and there were BNC terminated RG-59,

75 ohm cabling. The 75 ohm, being higher impedance had a smaler center pin so if you intermixed your cabling you tended to ruin all your video cables by spreading the center pin connection, making it loose later. Especially happened when using barrels willy-nilly. I heard the problem since has been fixed in some way and adapters of the 75 and 50 system can be intermixed with impunity.

Has it been fixed?

I'll rephrase the question, it wasn't very clear.

The male screen connection is a tube which slides inside another tube on the female. Is the contact supposed to be made between the male outer and female inner tube surfaces, or between the male tube end surface and the female end surface?

Like this?

FFFFFFFFFF MMMMMMMMMM F

MMMMMMMMMM F FFFFFFFFFF

Or like this?

FFFFFFFFFF F MMMMMMMMMMF

MMMMMMMMMMF F FFFFFFFFFF

(not to scale)

If the former, it's not very good as they're often quite a loose fit. If the latter, then some of my plugs must be slightly short.

Is there a standard?

Cheers

--
Syd

On the female BNC connecter there is the center pin, surrounded by a gap and then insulation, and then this is surrounded by "spring fingers", then there is the gap that the male cylinder fits into. My understanding is that it is these spring fingers engaging the inner surface of the male cylinder that makes the connection.

I'll rephrase the question, it wasn't very clear.

The male screen connection is a tube which slides inside another tube on the female. Is the contact supposed to be made between the male outer and female inner tube surfaces, or between the male tube end surface and the female end surface?

Like this?

FFFFFFFFFF MMMMMMMMMM F

MMMMMMMMMM F FFFFFFFFFF

Or like this?

FFFFFFFFFF F MMMMMMMMMMF

MMMMMMMMMMF F FFFFFFFFFF

(not to scale)

If the former, it's not very good as they're often quite a loose fit. If the latter, then some of my plugs must be slightly short.

Is there a standard?

Cheers

--
Syd

On a sunny day (Fri, 14 Nov 2014 13:15:02 +0000) it happened Syd Rumpo wrote in :

Is it possible you have a mixed set of 75 Ohm and 50 Ohm connectors, or even 95 Ohm?

See the picture next to 'Types'.

I think we have our sexes mixed up, but on my males (your females?) the 'spring fingers' aren't sprung outwards at all.

The ID of the female is about 8.25mm and the OD of a male (across the fingers) is about 7.75mm, although I can't get the calipers in to be very accurate. This seems about universal for the half dozen or so I've looked at.

Seems that proper mating involves a degree of good luck.[1]

[1] I said _quiet_ at the back!

Cheers

--
Syd

They're all 50 ohm, but nowadays they should be compatible anyway.

Cheers

--
Syd

Yes.

The idea is constant impedance, which means the same diameter ratios and sizes all the way through.

The inner tube of the male is a spring fit inside the female tube, but it is important that the end of the male tube butts up against the back of the female tube to ensure that constancy of diameter, but I had to pick up one of each here to confirm that.

It's not a spring fit on any of mine, it's consistently loose. However, what you say makes sense, that in order to maintain a constant diameter, the end face butts up against the back of the female.

Cheers

--
Syd

Sorry, was in a hurry and fubared the m/f. I believe that the fingers are tapered (conical) so as you push the two together the fingers engage the inner surface tighter and tighter. I could be wrong, it's been a while since I accidentally ripped a bnc apart :-), but that's how it was explained to me when I first started using them. The top should be a little small to easily enter the cylinder, but down at the bottom they should be tight.

I think we have our sexes mixed up, but on my males (your females?) the 'spring fingers' aren't sprung outwards at all.

The ID of the female is about 8.25mm and the OD of a male (across the fingers) is about 7.75mm, although I can't get the calipers in to be very accurate. This seems about universal for the half dozen or so I've looked at.

Seems that proper mating involves a degree of good luck.[1]

[1] I said _quiet_ at the back!

Cheers

--
Syd

Then it is almost certain that you are mixing up 50 and 75 ohm variants. (Someone else mentioned 93 ohm; not come across those)

Back to the history lesson, Neill invented the N connector, and Concelman the C connector before they joined forces for the BNC & TNC.

Otherwise the N connector is so-called because in mathematical terms, there are N different ways to put it together, and all of them wrong!

:-)

At the bandwidth of BNCs, there's no reason to change the center pin size. A fraction of an inch of a small mismatch won't matter.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

[snip]

I've used 93 ohm BNC for ARCnet. It was a 2.5Mb/s token passing network, popular in the '80s. It disappeared when Ethernet became the predominant LAN technology.

Allan