SMA edge launch

Or

SMA connectors been around since the late 1980's to my certain knowledge, and probably quite a bit longer. What's your point?

Am 28.06.21 um 03:44 schrieb Bill Sloman:

That they are > 10 dB cheaper nowadays than they used to be?

Gerhard

Not a point that he made explicitly. SMA - with it's turned screw attachment - is never going to be all that cheap. Presumably the market is a lot bigger now than it was in the late 1980's when GHz semiconductors were thinner on the ground, and also rather more expensive.

The price ratio is 1800:1.

I don't think you could tell the difference up to 5 GHz or so. Those cheap Amazon edge-launch SMAs seem to be pretty good.

The center pin tends to be fat, but if you handle the layout right it's almost invisible on a 20 GHz TDR.

I think the Chinese gold-colored SMA connectors are stamped, not turned. Sure the quality is bad, but for many applications it does not matter.

SMB and SMC were intended to be the cheaper, lower performance variations of the SMA-sized connector. If you want cheap, it probably isn't a good idea to go for stamped parts that are intended to look like higher-quality parts without delivering the essential dimensional accuracy

I bought some fairly nice fat binding posts in China- the metal part appears to be cast rather than a screw-machined part. It's good enough for the purpose.

thicknesses. I bought mine from Ebay.

Precision casting can presumably be made more precise if you throw enough technology at it. It's certainly a lot quicker than machining. Once you get up to GHz frequencies, the critical dimensions of the insides of your connectors are going to have to be pretty precise.

My management makes engineers send a request email to have someone pull a part from stock for us, which can take 10 minutes, in theory. So we have a private stock of parts kits and hardware and stuff. I buy these types of SMA connectors from Amazon, and cables and adapters too, random brands, and they have always been fine. I TDR them for high-speed behavior and they are always good. Something that small almost has to be.

The attenuators can be mediocre.

The hazard with edge-launches is that if the board is a bit too thick, some connector ground prongs won't fit over the board. 65 mils thick max on the board, metal-to-metal, seems to be right.

Vbites are great but won't snap on if the board is thick. We remove the solder mask in the connector area, to save a few mils.

Somebody a bit more careful might not be quite as happy. "Always good" isn't a quantitative assessment.

Impedance discontinuities can be quantified, if you know what you are doing

At a low enough frequency.

When compared with what?

I suspect the items in question were zinc-cast, and it only takes two operations to precision bore and thread them; if you can get robots to fit the castings onto carriers, the machining is kinda cheap. Then it's off to nickel-plate and gold-flash. For cheap BNC, they didn't gold-flash.

Precision machining is required for every ballpoint pen, but... in quantity, that's not a high cost.

The Fairview has a SWR spec of 1.25:1 up to 27 GHz. The uncertainty is bounded for this portion of mismatch. (Granted, I am presuming that is a max number.) The SWR spec for the "QMseller" is... oh, there is no spec. No bound on the uncertainty. Probably no bound on anything. Maybe a few flakes strip off as you screw the cable on... lol.

I wouldn't say this is apples2apples if comparison is your point.