Don't buy SMA cable assemblies from CentricRF

[joeqsmith]

...
There are very high-end SMA connectors, some of which have a screw clamping system designed such that I believe won't allow the pin to move at all (unless not screwed down properly). Example is SV Microwave example: SMA male connector for RG178 and the assembly instructions do not mention having to set pin depth (unless I missed it). But I'm sure they will be exceedingly expensive.
...

I used similar connectors to make the cables for my first VNA.  The nut locks the braid in-place.   I've used this same style with BNCs.   

[shabaz]

Those are very decent plugs.. from the photo it looks they even have holes on the end presumably for aircraft style wire insertion to prevent accidental unscrewing!

[joeqsmith]

...
 I've done some digging but not exhaustive.

I really don't know.  This is why I am asking.  The MIL-STD that was previously linked is A, dating back to 1988.  I would need to start with current specs.   It is a bit hard to believe they would not allow for any hardline.  This type of coax is used in a lot of equipment.  The coax center conductor is formed into the male pin.  Steps cause reflections.  Maybe back in 1988, it wasn't much of a problem.   

Does MIL-STD-348 not allow for hardline? Can you point me to that? I was under the impression it only covered the interfaces, not the cables attached to the connectors. I took another look and couldn't find any sort of restrictions on cables. But I do have the latest -348 standard and have referenced that.

For what it's worth, based on MIL-STD-348 I still think a stepped center contact is the only "standard" configuration, so I don't see how someone could claim adherence to that standard and use an alternative.

I haven't read this standard nor am I the one who referenced it.  It's not anything I've used for work.  My only knowledge about it was skimming for SMA, and glancing at the couple of drawings.   I assumed you were an expert with it, or at least were required to meet it, and understood the content but is seems we are in the land of opinions and feelings.  If its for home hobby use, who cares....

I assumed with them being bad, you would pull them apart and post a side profile of the pin.   If they are bad, there's not much reason not to dissect them. 

I did go to their site and look up the PNs but they don't supply any details on the connectors used.   Looking at several part prints, I have not found any that show the dimensions of their pins.   Nor could I find a dimensional drawing for your gage.  Worse, it appears the distance from the start of the step to the tip of the pin varies.

So I really have no way to know if the gage would work with all the countless stepped pins out there.  My first step would be to call Maury and ask about compatibility with all these new pins that are out there.

Ah ok I see what you want. I haven't pulled one apart yet, but I did look at it (intact) under a microscope and it really appears to be a flat step. Maybe I'll pull one apart. If I do, I'll post pictures.

Wiki SMA shows a cutaway someone made.   Crazy these things work at all.   Then again, the Maury paper I uploaded sums it up

A basic fact remains: the SMA was designed as an economical, miniaturized, easy-to-use connector for system application — it was never intended to be a precision connector for the laboratory.

Why can't the stepless gage be used across the board?  If it is from the outer contact to the tip, this is really all you want to know?

Not entirely. There are a number of ways an out-of-spec connector could damage another connector. Confining the discussion to pin protrusion specifically, it's my understanding that there are two possible mechanisms of damage here. One, as I believe you're pointing out is the tip of the pin protruding beyond the tip/valley of the mating socket. This would place pressure on the socket at its base. The other (and what I believe is typically referred to for pin protrusion) is what I'm referring to and is the step extending beyond the mating plane. This would exert pressure on the socket at the tip of the female fingers. This could cause the fingers to splay or otherwise be pushed out of normal alignment. I believe this is a greater risk too. It's probably not too difficult to bend fingers, but if you're just pushing into the base of the socket, I think that would be less likely to do damage. If you look at the interface dimensions too, the socket is specified to be longer than the max length of the pin. The total pin excursion from the reference plane, including the chamfer can be no longer than 0.1in. The socket, excluding the chamfer, must be at least 5mil longer. So there's at least 5 mil of leeway there (more if you account for the female socket chamfer). By contrast, the pin step can be up to the reference plane on both the male and female connector. So, if the male step goes past the reference plane and the female connector is at the reference plane or behind but by less than the male step, they will bump up against each other before the reference planes mate and damage can occur.

In any event, that's a long-winded way of saying ensuring the tip of the pin does not protrude too far does not guarantee that the step does not protrude excessively.

Isn't the tip to the stepped flat controlled?  From there wouldn't we know the step to the outer conductor?   Maybe it is not controlled. 

That document was just the basics and covered a lot of facets.   I am not suggesting temperature is the cause of what you are seeing.  Actually, I would think the main sources of error would be poor cleaning, handling, wear. 

Yep I hear you. Cleaning/handling/wear can't account for issues with the cable assemblies because I got the same results on brand new assemblies. These had quite literally never been mated before I gaged them (unless the manufacturer mated them). Now this could explain results with the gage, but I have a microscope to inspect the gage surfaces and ensure they're clean and a dental air compressor to clean them along with fine-tip q-tips. Moreover, as mentioned I got expected results with other connectors so I think the gage is fine.

It's just a basic how to guide.  It does not suggest you have a problem with your measurement.  Not being present at the time you measured them,  I have no idea what was done.  I am merely asking questions to paint a clearer picture.  Again, don't take it to suggest you did anything wrong or that I am some fan boy of the brands you have looked at and believe that everything is fine in the world.   

I am also not apposed to pointing out problems and calling out specific companies.   This is often the case when reviewing various brands of handheld multi-meters.  I tried to be unbiased, transparent, and present only the data.   

[matthuszagh]

I haven't read this standard nor am I the one who referenced it.  It's not anything I've used for work.  My only knowledge about it was skimming for SMA, and glancing at the couple of drawings.   I assumed you were an expert with it, or at least were required to meet it, and understood the content but is seems we are in the land of opinions and feelings.  If its for home hobby use, who cares....

You said "It is a bit hard to believe they would not allow for any hardline" when discussing MIL-STD-348. Where does this statement come from? It kind of sounds like you're pulling this out of thin air. I'm not an expert in -348 but I am familiar with it. When you make statements like that I try to accommodate the fact that maybe there's something I missed. But let me be clear, the standard only covers the dimensions of mating surfaces. There is very little discussion of cables (apart from a reference to documents that do discuss cables). Nor is there a discussion of non-standard center pin features such as stepless or angled steps. However, the diameter of the "stepped" part of the center pin is not dimensioned, so perhaps it's possible to take some creative liberties there as long as no part of the step (if it exists) extend beyond the reference plane.

Also, instead of asking me about it and then criticizing my understanding of it, how about you just read it too? The section covering SMA connectors is only several pages and simply consists of mechanical drawings.

Isn't the tip to the stepped flat controlled?  From there wouldn't we know the step to the outer conductor?   Maybe it is not controlled. 

No it isn't. But this doesn't even make sense. It's a mechanical drawing. In precise mechanical drawings you give ranges, not exact values. An exact value would be a bit ludicrous. In any event, in this case, the pin length is constrained by a min length of the cylinder and a max length of the pin including chamfer (from the reference plane). The chamfer angle and diameter of the tip are also constrained. But just read the document.

It's just a basic how to guide.  It does not suggest you have a problem with your measurement.  Not being present at the time you measured them,  I have no idea what was done.  I am merely asking questions to paint a clearer picture.  Again, don't take it to suggest you did anything wrong or that I am some fan boy of the brands you have looked at and believe that everything is fine in the world.   

I am also not apposed to pointing out problems and calling out specific companies.   This is often the case when reviewing various brands of handheld multi-meters.  I tried to be unbiased, transparent, and present only the data.

You've misinterpreted my tone. I accepted your previous explanation that these are merely questions. And, in turn, I am simply answering them. I'm not sure why my last message made you so annoyed.

[KE5FX]

That same group wrote a paper on proper care in the lab that is also pretty good.  Guessing a paper like this helped curb the damage caused by the students.

That's a great document, except for the superstitious just-so story about how the torque wrench should be held.  The breakover point is independent of leverage, which is the whole idea behind a torque wrench.  If anything, it's easier to apply forces in undesired directions if you hold it at the very end of the moment arm. 

It would be better to advise students to cultivate a sense of the force magnitudes and directions that are being applied to the connector, and to simply stop turning the wrench at the moment of breakover, regardless of how/where they're holding it.  Hard enough to teach 'mechanical sympathy' without telling people to use only the last 10mm of the wrench handle.

Another nice presentation surfaced on the WA1MBA list the other day: Signal Microwave connector basics (10 MB .PDF).  It's not new but that's the first time I'd run into it.

[joeqsmith]

I haven't read this standard nor am I the one who referenced it.  It's not anything I've used for work.  My only knowledge about it was skimming for SMA, and glancing at the couple of drawings.   I assumed you were an expert with it, or at least were required to meet it, and understood the content but is seems we are in the land of opinions and feelings.  If its for home hobby use, who cares....

You said "It is a bit hard to believe they would not allow for any hardline" when discussing MIL-STD-348. Where does this statement come from? It kind of sounds like you're pulling this out of thin air.

Finding something hard to believe, doesn't suggest fact.   It was followed with:

This type of coax is used in a lot of equipment.  The coax center conductor is formed into the male pin.  Steps cause reflections.   Maybe back in 1988, it wasn't much of a problem.   

I'm not an expert in -348 but I am familiar with it. When you make statements like that I try to accommodate the fact that maybe there's something I missed. But let me be clear, the standard only covers the dimensions of mating surfaces. There is very little discussion of cables (apart from a reference to documents that do discuss cables). Nor is there a discussion of non-standard center pin features such as stepless or angled steps. However, the diameter of the "stepped" part of the center pin is not dimensioned, so perhaps it's possible to take some creative liberties there as long as no part of the step (if it exists) extend beyond the reference plane.

Again, I wasn't sure if the drawings referenced in the standard were showing what the parts need to mate to or if this was the requirements for the parts themselves. 

Also, instead of asking me about it and then criticizing my understanding of it, how about you just read it too? The section covering SMA connectors is only several pages and simply consists of mechanical drawings.

It wasn't my rabbit hole to chase down.  I assumed you had and would know the basics.   

Isn't the tip to the stepped flat controlled?  From there wouldn't we know the step to the outer conductor?   Maybe it is not controlled. 

No it isn't. But this doesn't even make sense. It's a mechanical drawing. In precise mechanical drawings you give ranges, not exact values. An exact value would be a bit ludicrous. In any event, in this case, the pin length is constrained by a min length of the cylinder and a max length of the pin including chamfer (from the reference plane). The chamfer angle and diameter of the tip are also constrained. But just read the document.

I wonder why Maury supports measuring the contact pin location.

It's just a basic how to guide.  It does not suggest you have a problem with your measurement.  Not being present at the time you measured them,  I have no idea what was done.  I am merely asking questions to paint a clearer picture.  Again, don't take it to suggest you did anything wrong or that I am some fan boy of the brands you have looked at and believe that everything is fine in the world.   

I am also not apposed to pointing out problems and calling out specific companies.   This is often the case when reviewing various brands of handheld multi-meters.  I tried to be unbiased, transparent, and present only the data.

You've misinterpreted my tone. I accepted your previous explanation that these are merely questions. And, in turn, I am simply answering them. I'm not sure why my last message made you so annoyed.

It wasn't annoyed.   I was only stating that I have called out companies in the past as well and am not apposed to it.  In doing so, I show every painful step along the way.   

[joeqsmith]

That's a great document, except for the superstitious just-so story about how the torque wrench should be held.  The breakover point is independent of leverage, which is the whole idea behind a torque wrench. 

I think that came right out of the Keysight manual.  You think the location where you apply the force to the torque wrench's handle has no effect on the applied torque and this is superstition? 

***
Video from Maury doing a repeatability test.  I've never seen anyone line their wrenches with Kapton tape before, even when working with metrology grade parts.  He mentions proper hand placement on the wrench.   

[KE5FX]

I think that came right out of the Keysight manual.  You think the location where you apply the force to the torque wrench's handle has no effect on the applied torque and this is superstition? 

Yes, it's superstition.  That's not how a torque wrench works.  If you disagree, enlighten us.

Video from Maury doing a repeatability test.  I've never seen anyone line their wrenches with Kapton tape before, even when working with metrology grade parts.  He mentions proper hand placement on the wrench.   

Yes, you can use a torque wrench incorrectly.  Where you hold the handle has very little to do with that, though.  (I mean, look at your own video thumbnail, for Pete's sake.)

Look, it's a good document.  I don't disagree with 99% of it.  But it's 60 pages long.  They are damned lucky if a student makes it past page 6.  Leave out the part about using epoxy and wire to make cables, and clean up the part about how to hold a torque wrench, and... the students still won't make it that far.  BT, DT.

[joeqsmith]

I think that came right out of the Keysight manual.  You think the location where you apply the force to the torque wrench's handle has no effect on the applied torque and this is superstition? 

Yes, it's superstition.  That's not how a torque wrench works.  If you disagree, enlighten us.

Video from Maury doing a repeatability test.  I've never seen anyone line their wrenches with Kapton tape before, even when working with metrology grade parts.  He mentions proper hand placement on the wrench.   

Yes, you can use a torque wrench incorrectly.  Where you hold the handle has very little to do with that, though.  (I mean, look at your own video thumbnail, for Pete's sake.)

Look, it's a good document.  I don't disagree with 99% of it.  But it's 60 pages long.  They are damned lucky if a student makes it past page 6.  Leave out the part about using epoxy and wire to make cables, and clean up the part about how to hold a torque wrench, and... the students still won't make it that far.  BT, DT.

Youtube randomly creates thumbnails for you.   It will be difficult to over torque the connector when you are loosening it.   (notice how he flips the wrench when loosening)     

We had this discussion back in 2019.

https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg2666421/#msg2666421

Five years later, I continue to disagree with you, and as before:

Again, you can lead the horse to water....  But I can't help you. 

This also came up during the search:
https://www.eevblog.com/forum/rf-microwave/experiment-testing-the-effects-of-releaving-ground-plane-beneth-a-component/msg3609102/#msg3609102

[KE5FX]

Yep, that's why I baited you when the subject came up again.     Answer with math rather than homilies, and we can avoid revisiting the issue in 2030.

[joeqsmith]

Yep, that's why I baited you when the subject came up again.     Answer with math rather than homilies, and we can avoid revisiting the issue in 2030.

You had posted a link to a torque wrench which is similar to the one I had used in that demonstration where I showed the effect of different hand placements.  Hardly homilies.   Of course, you could show me the same wrench you linked without having any effect. 
https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg2666592/#msg2666592

https://www.fairviewmicrowave.com/product/rf-connector-accessories/rf-connector-torque-wrenches/sma-connector-torque-wrenches/sma-fixed-torque-wrench-click-st-sma3.html

***

[Smoky]

Another series of Amphenol SMA cables that I bought on sale from Arrow are these .085 semi-rigid Anti-Torque versions. Very nice cables:



They have a 1/4" hex molded into the stainless steel body of the connector to keep it from spinning.



These cables are tested to 18GHz and have other design requirements too. I bought 51 cables of various sizes between 3"and 10" long.



I payed less for these cables than items you'd find on a McDonald's Happy Meal menu

[KE5FX]

You had posted a link to a torque wrench which is similar to the one I had used in that demonstration where I showed the effect of different hand placements.  Hardly homilies.   Of course, you could show me the same wrench you linked without having any effect. 

Sure, when installing lugnuts with an automotive torque wrench, you might want to keep the math described in the video in mind.  (Not the first time this week I've wished for a 4x speed setting...)

Now, take another look at the SMA torque wrench from Fairview Microwave.  Where is the pivot point on that one?  Hold it anywhere on the red plastic handle, and it will work just fine.

[joeqsmith]

You had posted a link to a torque wrench which is similar to the one I had used in that demonstration where I showed the effect of different hand placements.  Hardly homilies.   Of course, you could show me the same wrench you linked without having any effect. 

Sure, when installing lugnuts with an automotive torque wrench, you might want to keep the math described in the video in mind.  (Not the first time this week I've wished for a 4x speed setting...)

Now, take another look at the SMA torque wrench from Fairview Microwave.  Where is the pivot point on that one?  Hold it anywhere on the red plastic handle, and it will work just fine.

Then prove it to us.

[KE5FX]

Honestly?  Can't be arsed.

[Smoky]

Now that I've looked at this cross-section of a "typical" SMA connection:



IMHO, as long as there is no debris interfering with the leading "ring" edge surrounding the plug's dielectric and the shoulder of the receptacle, finger-tight is all that should be needed to seat this connection.

I think a compact tool similar to a bicycle spoke wrench but with ears like you'd find on a water hose bib made with Delrin that slips over the hex of the SMA connector like a flare nut wrench just to give a better sense of "feel" of the slight leverage/torque that's applied is all that's needed to do the job of seating the fitting 99.999% of the time in a typical office/testing environment

I see no reason to put a scratch on the finish of that beautiful shiny nut with a torque wrench.

No two fittings will ever be the same, nor will any two connections.

The weakest possible link I see in that picture would be if you scored a ring around the copper/gold plating that's around the center conductor of the cable when the dielectric is stripped off.

I'd just make sure the shoulder of the center contact in the plug is flush or slightly under the surface of the dielectric.

If a better connection would need to be made, do away with the fitting and solder the cable directly to the board where it needs to go.

People are spending hundreds of $'s on torque wrenches for this

[KE5FX]

The important thing with regard to connector torque (besides avoiding damage) is to ensure that it doesn't come loose at an inopportune time.  A finger-tight connection can be loosened with the same fingers, or by otherwise applying roughly the same amount of torque (say, by inadvertently twisting the cable slightly when you move it.) 

What you find when you use an SMA torque wrench is that the connectors are not much more than finger-tight -- just tight enough to keep you from loosening them with your fingers.  Over time you grow to appreciate the added connection reliability.  Good habits really pay off here.

It's a statistical thing -- you can catch one loose SMA connector easily enough yourself, but when you have 100 connections that you're not confident in, you have a real problem.  Ask the CERN folks about that...

[nctnico]

Yep, that's why I baited you when the subject came up again.     Answer with math rather than homilies, and we can avoid revisiting the issue in 2030.

You had posted a link to a torque wrench which is similar to the one I had used in that demonstration where I showed the effect of different hand placements.  Hardly homilies.   Of course, you could show me the same wrench you linked without having any effect. 

That is interesting indeed. As I understand it, the cause of the difference in force is because the pivot point of the force on the clutch is different from the pivot point formed by the socket (which extends out a bit further). Then again, the 'click' style torque wrenches are regarded as amateur tools by professionals. Probably for this very reason.

[tautech]

People are spending hundreds of $'s on torque wrenches for this

You certainly can but don't really need to. 
https://www.ebay.com/itm/353942090527?

Spanner head is a little rough and could be finished much better but luckily I have another to check its torque calibration from a $$ Cal kit.

The arrival surprize was the nice case it arrived in, well not a case as such but a 2 piece slide together tube like big drill bits, threading taps and lathe tools come in.
This bit dearer one shows the case:
https://www.ebay.com/itm/315751197899?

[KE5FX]

That is interesting indeed. As I understand it, the cause of the difference in force is because the pivot point of the force on the clutch is different from the pivot point formed by the socket (which extends out a bit further). Then again, the 'click' style torque wrenches are regarded as amateur tools by professionals. Probably for this very reason.

The difference between holding the wrench at the very end and holding it like a normal person would hold it amounts to the square root of jack squat. 

Although I'm curious, what other kinds of torque wrenches for small coax connectors are there, besides the click/breakover variety and the axial key variety?  Do the real pros use something else entirely?   

[joeqsmith]

That is interesting indeed. As I understand it, the cause of the difference in force is because the pivot point of the force on the clutch is different from the pivot point formed by the socket (which extends out a bit further). Then again, the 'click' style torque wrenches are regarded as amateur tools by professionals. Probably for this very reason.

The difference between holding the wrench at the very end and holding it like a normal person would hold it amounts to the square root of jack squat. 

Although I'm curious, what other kinds of torque wrenches for small coax connectors are there, besides the click/breakover variety and the axial key variety?  Do the real pros use something else entirely?   

Rather than wasting your time posting your political dribble, which admins have to delete, do something useful and prove it.   

[joeqsmith]

People are spending hundreds of $'s on torque wrenches for this

You certainly can but don't really need to. 
https://www.ebay.com/itm/353942090527?

Spanner head is a little rough and could be finished much better but luckily I have another to check its torque calibration from a $$ Cal kit.

The arrival surprize was the nice case it arrived in, well not a case as such but a 2 piece slide together tube like big drill bits, threading taps and lathe tools come in.
This bit dearer one shows the case:
https://www.ebay.com/itm/315751197899?

I bought one of their wrenches.   For the price, it's decent quality. 

[KE5FX]

Rather than wasting your time posting your political dribble, which admins have to delete, do something useful and prove it.

Let's try to stay on topic; feel free to take personal insults to PMs where I'm the only one who has to ignore them. 

Bear in mind that I didn't assert that torque wrenches need to be held this way:



... and I'm also not the one who leaps to the defense of such an absurd notion every time it comes up. 

Like I said, math or GTFO.  Preferably math not involving wrenches sold at Harbor Freight.

[joeqsmith]

Calling out the thumbnail used for that video as evidence was pretty stupid on your part, but expected.   I suspect it was obvious he was removing the connector.   The math was fairly straight forward and so was the pivot point but again,  you appear more interested in pointing out your political views than discussing anything technical.   You're wasting your time.   

[joeqsmith]

...
I think a compact tool similar to a bicycle spoke wrench but with ears like you'd find on a water hose bib made with Delrin that slips over the hex of the SMA connector like a flare nut wrench just to give a better sense of "feel" of the slight leverage/torque that's applied is all that's needed to do the job of seating the fitting 99.999% of the time in a typical office/testing environment
...

We tried a few printed wrenches.  The biggest problem I see with these is they will wear fast, changing the torque.  You would be much better served going the route tautech shows.  Those wrenches can be adjusted.  You can always apply a little Kapton tape like that video I linked shows if the concern is with the surface finish.