Comment on What happened to cylindrical plugs?
litchralee@sh.itjust.works 2 days ago
A cylindrical connector would be fine for connecting one or two conductors. But more than that and it starts to become a nightmare to design, and even worse to build and use reliably. Classic examples include the venerable RCA connector, the BNC connector for radio signals, and IMO the worst connector to ever exist, the F-type connector used for TV coaxial cable.
With just two conductors, a cylinder can have have a concentric shape, where the inside is a pin and the outside is a shell. But you’ll notice that although all these connectors are circular, they’re hardly designed to rotate while attached. You generally have to remove or at least loosen them before trying to turn them. Or you still try it and the TV picture might flicker a bit. The problem is one of electrical contact.
The engineers that make connectors go through painstaking efforts to get the conductive surfaces to align – or “mate” as they say – because if they don’t, the signal quality drops like a rock. It’s already hard enough to get cheap connectors to reliably align, but now you want them to move relative to each other? That’s tough to build, and moving surfaces will eventually wear down.
Even worse is that circular shapes tend to have poorer mating, because manufacturing tolerances for curves is wider than tolerances for flat surfaces. We actually don’t want to make round contacts, if a rectangular shape would suffice. Flat contacts are simpler to produce and generally more reliable [citation needed].
But even more intractable is the matter of matching the pinouts. Here is the pinout when looking at the connector of a USB C cord:
USB C pinout when looking straight at a USB C cord
Even without understanding what each pin does, it’s noticeable that certain pins are the same whether you flip the connector over. In fact, they even label them that way: pin A12 on the top-right is also B12 on the bottom-left. The most damaging scenario is if USB 5v power was sent down the wrong pin, but it’s very clear that the VBUS pins – which are the 5v power – will always be in the same place no matter the cord orientation.
The only pins which are different upon inversion are the data lines – anything with a + or - in the name – or certain control signals which are intentionally paired with their opposite signal (eg CC1 and CC2). The USB C designers could have packed way more data pins if they didn’t have to duplicate half the pins to allow flipping the connector over. But that design choice has made USB C easier to use. A fair tradeoff.
And that’s the crux of it: in engineering, we are always dealing with tradeoffs, either for performance, cost to produce, ease of use, future compatibility, and a host of other concerns. Wanting a cylindrical connector could certainly be a design goal. But once it starts causing problems with alignment or manufacturing, there will inevitably be pushback. And it’s clear that of all the popular connectors used today, few are cylindrical.
Heck, even for DC power, the barrel connector has given way to more popular designs, like the Anderson PowerPole or the XT family of connectors, because the market needed high-current connectors for drones and Li-po batteries. Granted, the XT connectors are basically two cylindrical connectors side-by-side haha.
What’s your beef with the F-type connector? The centre pin is the coax core, compression tool to terminate the coax, solid connection, rated to some absurd frequencies, all round easy connector, no soldering or extra pin required.
Source: I installed two-way satellite dishes for a time and still use those connectors on my HF antennas as a radio amateur - yes, I know, 75 Ohm - can’t say it’s ever stopped my 10 mW beacon from being heard 13,945 km away.
In not the person you replied to, and I can’t speak about the engineering merits; but as a user I hate F-type connectors. They’re bad enough when you have to only install them once in the lifetime of the connected device - it’s the threaded screw that’s the worst, I think, for which no non-technical user owns a tool beyond their fingers, from which the bevel invariably strips the flesh; although I’ve also bent enough of those pins trying to get something connected in an awkward place, or because I was tired, or being sloppy. It’s not a connector that’s convenient for amateurs, and most of its users were and are amateurs.
As a connector for multiple, frequent dis- and re-connection, it’s an utter disaster. Sure, that’s not what it’s designed for. It was designed to be a semi-permanent extension of permanent wiring, and I’m sure it’s great at that.
The context of the whole thread, though, was end-user, repeated, frequent connections for people who have to be reminded by a manual that the thing needs to be plugged in. Coax is horrible for that.
The context of the whole thread, though, was end-user, repeated, frequent connections for people who have to be reminded by a manual that the thing needs to be plugged in. Coax is horrible for that.
so you want BNC
BNC is better, but I’ve only encountered it, like, twice.
Honestly, I’ve never been happier since USB-C took over. I compare today to the early 90s and having 8-12 different connectors - two of which looked identical but were incompatible - to hook up a single Sun workstation. I clearly remember dreaming of a day when there would be a single connector for everything, and we’re really close. Higher wattage demands and video connectors (HDMI, DP, DVI) are the only hold-outs - and I’m not sure why USB-C hasn’t conquered video yet, unless it’s a cost thing, because it’s certainly capable.
My primary complaint with the F-type connector is that it only does half the job: a proper connector should make a reliable and consistent mechanical and electrical coupling. For the latter, the F-type fails miserably, on account of having no protruding pin of its own: reusing the center conductor as a “pin” is at best slapdash, and at worst fails to account for inconsistent conductor cross-sections.
When affixing an F-type connector onto a new segment of coax, unless great care has been taken to slice the cable cleanly, the center conductor often ends up with a arrow-shaped tip which also flattens the round cross-section into an oval. This tip is now a minor danger to people, in addition to no longer being assumed as round. This certainly doesn’t help with reliable mating later.
Furthermore, a solid copper tip is not ideal for a connector, unless the opposite coupler that grasps the tip is made of copper as well. But copper can’t be used to make springy receivers, so inevitably another metal must be used. But the prevailing composition of contacts for connectors are either solid brass or are plated (eg gold). But a sharp copper tip will end up scratching the mating surfaces over time.
And this is just the start of the F-type’s follies. The user experience of turning a 7/16" fine thread in narrow spaces is exhausting. With no consistent specs for the F-type, some cheaper connectors have the thinnest possible hex head to fit a wrench on. Compression F-type is better, but then we have to compare to other connectors.
In the broadcast and laboratory spaces, BNC is the go-to connector, with easy mating and quarter-turn engagement. It also comes in 50 and 75 Ohm variants (albeit confusingly). In telecoms, the SMA connector is used for its small size, and larger coax might use the beefy N connector. Some of these variants are even waterproof. Solderless is an option. All these connectors are rated by their manufacturers for a minimum number of mating events.
In all circumstances, according to this chart, the RF performance of BNC, SMA, and N are superior to F-type, which has only ever been used for TV, CCTV, and certain low-frequency clocking systems. I’m not sure what you mean by “rated to absurd frequencies”, but surely SMA’s (up to) 25 GHz rating would be tremendously and wildly insane by comparison to 1-2 GHz for F-type.
So that’s my beef. It’s just a bad connector, used only because it’s cheap.
I saw that chart too. When you click on the F-type link you learn it’s rated up to 4 GHz. The summary table is off for several connectors.
You cannot argue that the mating is poor if it’s rated to 4 GHz.
There is nothing wrong with using the centre pin of the coax, it’s one less join in the chain and it’s rated at over 500 matings. It’s not for lab equipment, but if you want to connect something and leave it there for the next decade, there’s nothing better.
i keep hearing that F stands for Flimsy. no idea where that came from, unless something is seriously wrong with crimping technique. i guess there’s a tradeoff between CCS or copper cable with durability of pin/center conductor vs bending radius, and some people don’t like how it turns out, while ignoring that it’s cheap and not really designed for multiple disconnections
but yeah, as long as everything is matched good-enough then it’s a cheap way to connect low loss, cheap cable
For my shack where I move stuff around, testing gear, radios, switches, etc. I’ve standardized on SMA, on my feed line which hasn’t changed or been disconnected for a decade, F-type.
scheep@lemmy.world 2 days ago
woah that’s a very in-depth answer. yeah makes sense that cylindrical connectors aren’t actually designed to rotate a bunch. I assume it would be something similar to weird crackling sound when you turn an 3.5mm jack cable too hard?
litchralee@sh.itjust.works 2 days ago
I’m not sure how hard you’re rotating a 3.5 mm cable, but yes, that sound is the sudden making and breaking of the contacts, which it’s not meant to do. It will wear down the surfaces, even if the 3.5 mm tip is gold plated, since the gold is for anti-corrosion not for anti-friction.
But, the notion of cylinder housings for connectors has not died. After all, large cylinders are easy to grasp. Here is one very beefy example, often called the California Standard connector due to its use for Hollywood movie productions. This is a waterproof, twist-lock connector that also suppresses arcs if you unplug it while it’s still in. It heavy enough to probably also double as a blackjack for self-defense lol
Hubbel California standard connectors CS6365 and CS6364