What type of connector is this?

[greenstar]

I have bought a cheap Chinese frequency meter off eBay. The seller doesn't know the type of rf connector, describing it as 'sma' and 'standard', but it's a smaller size than my standard. Standard what? I'd like to find an adaptor, male sma type to plug into the thing to BNC so I can check my signal generators etc. I ordered a standard sma to BNC, no use at all as far too large. The female sma is about 5mm od on the board. Can see various adaptors but don't want to flounder about too much.
Or should I just unsolder the existing female outlet and replace with BNC, as will need to put in a box anyway? Are there any rf implications of doing that?

[Herald1360]

Certainly looks like SMA. Though that has a 1/4" 36TPI thread.

Just a thought- your standard connector wasn't F type perhaps- as used on satellite TV etc?

Removing it and adding a short miniature coax flylead to a BNC should be fine operationally.

[Alistair D]

Check out SMB and SMC connectors. They all look very similar.

Al

[emeritus]

Possibly a SSMA, a smaller version of the SMA, having a 10-36 UNS coupling thread. Unified No. 10 threads have a nominal diameter of 0.19", which is about 4.83mm. Extract from a current Radiall SSMA catalogue attached, showing dimensions.

[Radio Wrangler]

No, that's not SMB or SMC. I've used rather a lot of them over the years in both 50 and 75 Ohm flavours so I'm pretty sure.

The other connector that looks like an SMA is an APC3.5, but as it's got the same thread as an SMA and will mate with one it wouldn't matter too much, Also APC3.5s are a bit too expensive for the application.

Does it have the usual 5-pin throughhole board fitting so you could fit a real proper SMA?

David

[Diabolical Artificer]

I have a couple of these you can have, they're off satellite TV receivers. They're about 8" long. Drop me a PM if interested.

Andy.

[greenstar]

Thanks folks, David, it does have five pins, four corners of a square with one in the middle. I take it then i could just drop a regular sma pcb female into the holes.
SSMA sounds likely - just checking, would those have the same holes?
Andy, if it's not an unanswerable question, what do you have that's 8 inches long? I can't imagine how it relates to the unit!
The other way, thanks Herald, is to obtain a BNC socket I can screw to the box I will need to make to put it in.

[Techman]

These are good little units at the price (how do they do it?). They, and their special socket, have already been covered on the forum a few months back if you have a look.

You’ll need to calibrate it against a ‘known’ accurate frequency source if you want the last two numbers on the display to mean anything.

[Techman]

I managed to find the previous thread, as usual it was a little longer ago than I thought!

Reading quickly through it, I’m not sure that there was ever a definitive conclusion as regards the socket. I bought one and I have to admit that I just use it with a wire bodged into the existing socket and have still to mount it into a small case with proper connections where I’ll probably do away with that socket. I was running mine from old re-chargeable PP3 batteries, but found that it really did need the full 9 volts and not much below to work reliably. Looking at the little regulator on the board, it’s actually good for working on higher voltages and I mostly run mine on 12 – 14 volts and it works well. It certainly did need calibrating to take accurate measurements, well that’s what I found with the one I got.

Link to previous thread:-

https://www.vintage-radio.net/forum/...d.php?t=112170

[emeritus]

Here's a link to the Radiall SSMA catalogue. It has drawings of their connectors and adaptors, but they do not appear to do a PCB right angle connector of the type shown in your photo.

http://www.radiall.com/media/files/SSMA%20D1121CE.pdf

[greenstar]

I must admit that I got it as I thought a modern thing would be as accurate as i need - I have various antique scopes and generators and using one to check another thought to get something as a more recent guide. I don't think it needs to be really accurate, whatever that means. Yes, thanks for the thread, I had not found it. I guess the other thing I will need is a probe sos I can use it on valve gear. Or something I can put in the box between it and the BNC connector I will get. This has been mentioned, but what i really need is a circuit. Many thanks.

[Techman]

I doubt there will be any circuit available for it, but you never know.

It shows I've not been keeping up lately, as while looking round the forum I've just seen yet another (very recent) thread on the same thing:-

https://www.vintage-radio.net/forum/...d.php?t=120187

[Radio Wrangler]

That's a common hole pattern for SMA, SMC, SMB, QMA and similat connectors, assuming it's the usual dimensions. It's handy because you can change things to whatever you prefer.

Some scopes (not many, though) have a signal output on their Y amp... a great front-end for counters.

David

[turretslug]

If you do a bit of searching on eBay, it's possible to find a good selection of suppliers offering the various small co-ax types to bulkhead BNC (sometimes others) with varying lengths of good-integrity miniature GHz-type coax cable already fitted for encouragingly low outlay. I've used these and been impressed by the quality and value- with the proviso of unpredictable, though generally not bad, delivery times from across the seas.

As regards the SMB connector (push-on and click, not the screw-on of SMA, and frequently found on DAB and GPS modules, amongst others) beware that there at least four different sizes of this type of connector ranging from impossibly tiny to near "Belling-Lee" size, SMB being (possibly!) the second or third smallest in the range. Suppliers aren't always certain of the correct designation for size themselves and even a good-res picture comparison to BNC isn't always conclusive. Been there....

A ready-made flying lead adapter also removes the possibility of blasphemy associated with making up tiny, intricate coax connectors

[greenstar]

I think, given the difficulty of defining the connector on this counter, what I will do is have it off and wire up a BNC on the outside of the box, as Herald suggests in '2'. This still leaves the problem of not frying it when connecting to valve circuits. It's not much use to me soley for transistor kit as I don't have any. This has been discussed before in a general sense, but suggestions would be most helpful.

[dseymo1]

A pair of inverse-parallel diodes across the input?

[Radio Wrangler]

Use a scope probe AND the diodes

David

[greenstar]

Sorry to be thick ... that is .... as below?

1n4007's?

[Silicon]

You need to reverse one of the diodes.

They will then provide a degree of protection if the signal goes above 0.5V in a positive or negative direction.

[Radio Wrangler]

1N4007 are power rectifiers. They seem to have become the de-facto standard for some reason, but they are rather slow diodes and fairly high capacitance. They won't leave much high frequency content for your counter to count. Think in terms of fast switching diodes.

David