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The BNC Connector and How It Got That Way (hackaday.com)
71 points by sohkamyung 23 days ago | hide | past | web | favorite | 40 comments

I too felt the author’s snobbery towards lesser connectors. I felt the same way towards equipment that did not have SDI as well. As cool as HDMI is, the connector is just not a secure attachment. It is today’s equivalent of the yellow/red/white video/audio jacks of older equipment. It is too easy for it to be pulled out accidentally. The twist lock secured connection of BNC is just reassuring.

Just about any connector can be converted into a locking and secure connector, such as the following CAT6 locking connector that is used significantly in live broadcast applications:


As for HDMI, it has incredibly few uses into terms of professional production (outside of connecting monitors) setups, but still can be made secure, as seen here: http://www.hallresearch.com/img/products/C-HDMI-L_connected....

Interesting. For live audio work I've usually encountered Ethercon (basically XLR with a CAT6 connector in the middle):


Ethercon really is a fantastic connector. I had a client who were working on industrial systems that lived in harsh environments, and recommended it to them. They ignored me on their first model, and used the connector quite successfully on rev 2 after they had a ridiculous number of field failures using normal Ethernet jacks.

My wife does AV production work and loves them too. Plus, in a pinch, you can just use a regular old Walmart Ethernet cable. Really handy to have a fallback (unlike e.g. XLR, where you're trying to find a pro audio shop)

I saw one of these for the first time just last week. Patching a laptop into a DMX light controller.

SCART is another disgusting connector that European readers will be familiar with. I like the idea of combining multiple video formats with sound as a predecessor to HDMI, but the least they could have done was put a decent D-sub or the Amphenol-style ribbon connector.

I recently got pretty heavily into SCART connectors because of retro video game stuff (the most common rgb connector you can use with older consoles is scart) and after a few months I've thrown it all away in exchange for special component cables instead because scart is just terribad in terms of staying connected.

Can't count the number of times I've had colour production go wonky just because of a tiny bump of the scart cable.

Connected a SCART TV and STB when I first moved to France. The cable was stiff, heavy, and unwieldy and it neve quite fit once everything was pushed back into the cabinet.

I was in college in the mid-90's, and scrimped and saved at one point to buy myself a 17" monitor [1]. (A big deal at a time when 14" and 15" were typical.)

I remember being pretty impressed that that the cable connected to the monitor with five BNC connectors rather than the usual VGA port or termination inside the monitor case. (Of course I doubt it did me any good at all b/c I just connected it to an ordinary VGA port on the other end.)

1] A Sony GDM-17SE1 if anybody remembers those. (Couldn't quite swing the slightly nicer Nanao FlexScan that could do native 1600x1200.... but the Sony was an excellent display anyway.)

Boy do I remember these. Analog component inputs. Essentially RGB+Hsync+Vsync. Or more correctly, YPbPr,H,V if I got the abbreviations correct.

I used to crimp/solder BNCs to cables, and I was so happy when we could switch to SDI instead of analog video cables. Each cable for the analog component video cables had to be the same length (within a very small tolerance) or the signals would be out of sync causing the color to not be reproduced correctly. Some devices had timing that you could adjust to compensate, but cable length was important. If you screwed up one of the cables and needed to cut off a bit to redo the end, you had to do the same "correction" to all of the other cables to match.

Oh how I miss the Trinitron. I too had one early on, a 19" model circa 1999/2000ish. It was stellar--mine had the 5 BNC and VGA input, of course I used the VGA too :D

> I too had one early on, a 19"

I bought my 17 in around 94-95 and used it for at least five or six years. It started out attached to a 486/33 and wound up attached to a P5/100 and then a custom K6/233 I bought when I got my first job, had for about a month, and then sold to buy a Thinkpad 560. (The same job that paid for the fancy desktop also kept me away from it, so I never really used it.)

It was probably around the same time you had yours, but I briefly did buy another desktop machine with a Dell branded 19" Trinitron. It was also very nice, but weighed a ton. (It was also the last CRT I bought.... everything since has been various LCDs, and aside from some crappy TN laptop displays, it's generally been a big improvement.)

Edit: I should add about these Trinitron displays... there are people that complained about the stabilization wires on Trinitron CRT's. I was able to see them, but they weren't an issue and the rest of the display quality was so good it didn't matter anyway. (At least to me.)

DisplayPort has an (optional) locking connector

I can kind of understand why it is options. We have them in our conference rooms and I have seen too many locking display port cables just ripped out of laptops. Makes me cringe every time.

It's still rather fragile and a pain to terminate, which disqualifies it as a serious connector in my book.

Hope it's OK to go off topic a bit and vent my gripe about connectors: You bump the connector and destroy the printed circuit board that it lives on.

Well, at least I got an oscilloscope for free that way. The inputs were flakey, and it was rejected by the calibration service. I opened it up, and re-soldered the printed circuit mounted input connectors. Lovely scope.

I think it's very on topic - connector mounting and robustness is important.

BNC connectors hit a great sweet-spot of being cheap and easily available for bulkhead mounting. I've used them for power in data loggers before, since they're positive locking. Felt a bit dirty, but just pretended I was in a research lab where BNC for DC power is very common.

The interesting thing about BNC is that the strain relief is with the device chassis, not the boards themselves. This makes them enormously more robust than, say, a PCB mount HDMI or anything like that.

Reliability isn't really off topic when talking about connector design. Apparently there are possible tradeoffs between damaging the socket and the cable; IIRC micro-USB is designed to sacrifice the cable to reduce damage to the device.

Funny enough, I had a $1200 software-defined radio that was destroyed when the micro-USB3 connector ripped off the board, taking a bunch of traces with it. When I ordered the replacement, it came with a full-sized connector on it instead, with mechanical through-hole structural support. Some micro-USB connectors have the through-hole support, but many are pure SMT devices that will happily destroy your board with a sneeze.

I always thought that these were called British Naval Connectors and were developed for submarines. Not sure if I dreamt that or someone was having a laugh with me.

"Bayonet Neil-Conselman"! Huh, who knew?

Speaking of connectors, once upon a time there was the IBM PC RT, whose mouse and keyboard connected with these:


Those are the only connectors I've ever been able to plug into the back of a box, from the front, without looking. They were wonderful (he says, tha remembering at the time he was the guy who got to crawl around under peoples' desks).

I was eventually told that, because the actual connectors were the same, they had to add the keyed moldings to prevent the hardware from being destroyed by being plugged into the wrong spot.

>"Bayonet Neil-Conselman"! Huh, who knew?

Indeed, it has been "bayonet network connector" in my mind. Must have been some folk etymology that got stuck.

They forgot to mention the alternative TNC, "Threaded Neil-Conselman". Same connector dimensions but the barrel is threaded and the cable connector screws on.

I mostly see them used on smaller RF gear like WiFi antennas, and whip antennas on hand held radios. The threaded design provides a more secure mechanical attachment. The classic blue Linksys routers and AP's use a reverse TNC connector for the antennas.

They're actually still fairly common regarding aircraft radios. I see them daily working with avionics, though BNC is more common.

SDI is probably the main remaining prevalent signal being used with BNC connectors, and 12G-SDI is going to be its last hurrah. 25G/100G Ethernet and is rapidly displacing it.

The main thing SDI & coax has going for it is its robustness, especially for 3G-SDI signals, so I guess it will live on there. But BNC & SDI is on the way out, certainly for broadcast. Its so much cheaper to use Mellanox, 25G/100G Ethernet instead.

I'd assume it will be decades until BNC/TNC die off completely. I replaced one today on a Bell 205A1 helicopter, for the ELT. Given the standards for reliability (both in how well it must perform and how long it must last) aircraft OEMs aim for, I expect to work with them for the remainder of my career.

> Like all coaxial connectors, it was designed to present as little change in the characteristic impedance of the feedline as possible by keeping the spacing between the center conductor connection and the outer shell as close to the feedline dimensions as possible.

The above supposedly explains why coax is better for high frequency, but the sentence isn't parsing for me. Can anyone explain it a bit more?

The characteristic impedance of a cable is distributed and depends on things like the spatial relation of the connector to the shielding, other internal conductors, and what the cable insulator is made of. Changes in these parameters result in local impedance changes, when electrical signals propagate down and reach changes in impedance, it cause reflections which show up as noise and loss. The more abrupt and large the impedance change is, the more extreme the reflections will be. Connectors are basically a hotspot for changes in the physical dimensions of the cable as it connects to a receptacle. Higher frequencies are more sensitive to changes in the physical geometry because of their smaller wavelength. Most decent BNC connectors will work up until a few GHz, most SMA up between 10 and 20 GHz. N connectors work up to almost 30 GHz.

Also, it's better shielded than twisted pair.

It's funny, keeping everything else constant, the center conductor can move quite a bit away from the exact axial center of the shield before the impedance changes very much.

PS. Neill, not Neil

RF guy here: N connectors are widely used in all RF equipment and are vastly superior to BNC connectors. Good luck using a BNC connector above several GHz. The second best connector used in RF is the SMA. The third most common is the 7/16 which is horrible in my opinion to work with but necessary for large power transfer.

N connectors are robust, so they get used heavily in military applications and that scale of production makes them relatively cheap and the mil-spec they are produced to ensures that you don't get moding until 20 GHz. They are also huge and a pain to put on. BNC is great for what it was designed for. Fast, reliable, repeatable, connections in the 100's of MHz range.

HP/Agilent/Keysight uses a "Precision BNC" connector on their scopes that easily outperforms N-type connectors in frequency response but is rather expensive to produce.

SMA connectors are actually pretty crappy but are cheap, small, and ubiquitous. Their size and forgiving PTFE dielectric makes them very forgiving up to 10 GHz or so from a frequency response view point.

Really good high frequency connectors are going to be the precision connectors, 3.5mm 2.92mm etc. down to 1.0mm which can go up and over 100 GHz where you should really be using wave guides anyways. These types of connectors are very expensive so you rarely see them in production electronics unless absolutely required.

Always wondered about these. Fascinating read, thanks for submitting.

BTW is it time yet to improve on RJ-45? Esp as ethernet typically uses 4 wires - its ridiculously large.

Gig E uses all eight. Just learned this recently when some of the Wi-Fi access points in the office kept falling back to 100mbit

Not really, you can get about 20-30M with 10GBaseT, maybe more, which is far enough, beyond which fibre optic is a superior solution anyway.

the RJ-45 is 8 wires, 4 pairs, and is designed to be easy to connect up by field personnel, and be cheap.

This^ I actually quite like the design because it's so easy to create connectors in the field with a couple simple tools. Don't have to strip the conductors or solder anything, just cut the sheath off, align the wires and shove it into the crimper.

Edit: and all this with connectors that are dirt cheap.

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