Don't buy SMA cable assemblies from CentricRF

[matthuszagh]

TLDR: Gage the connectors of all SMA cable assemblies upon receipt, even from reputable manufacturers. Don't mate unverified cable assemblies with anything that is expensive or difficult to replace. "Reputable" manufacturers are selling SMA cable assemblies with pin protrusion. This practice seems to be quite common in my admittedly limited sample. I'm directly calling out CentricRF (Centric RF) in the title since I had some discouraging communication with them (more on this below), but I've also experienced the same problem with Mini-Circuits and Crystek.

Recently, I got around to using my Maury A027 kit to gage pin depth on a number of SMA cable assemblies I have. The results were discouraging. I have a number of C589-086 SMA cable assemblies from CentricRF, as well as FL141-12SM+ assemblies from Mini-Circuits, and 1 crystek ccsma18-mm-086f-24. I never bought cheap SMA cable assemblies from Amazon or alibaba believing that pin protrusion was confined to cheap cables. But, this issue seems to be similarly prevalent in $20-$60 cables from brand names. The Crystek and 3/4 minicircuits cables showed pin protrusion on at least one connector (up to about 4 mil). 6/8 centricrf cables showed pin protrusion on at least one connector. Below are all measurements for the CentricRF cables. I verified that my A027 gage was giving correct results by comparing several measurements against a much more accurate 3.5mm gage from an HP 85052B calibration kit. A negative reading indicates protrusion. All units in mil.

C589-086-48: -0.5, +2.0
C589-086-12: -1.5, +2.0
C589-086-36B: -1.0, +2.0
C589-086-36B: -3.0, 0.0
C589-086-60: -2.0, -2.0
C589-086-72: -1.0, -1.0

All of these cables are pretty lightly used. Some were mated just once or twice (like the crystek) and others just in the 10s of mating cycles (minicircuits and some of the centricrf cables). I've also measured the same pin protrusion on new cables from centricrf (more on that below), so I don't think wear explains these results.

I also gaged some very high quality cables I have like Gore phaseflex and H+S sucoflex, and unsurprisingly they're all spot on what they should be. These were all bought used and probably experienced many more mating cycles than the SMA cable assemblies mentioned above.

I think that manufacturers don't care about pin depth of their cheaper cable assemblies. That doesn't stop them from claiming conformance to MIL-STD-348. In my opinion this is dishonest (probably through negligence). It's difficult to imagine these manufacturers don't know to measure pin depth (minicircuits even sells gages). I do have 2 more expensive minicircuits cables (both ULC-1.5FT-SMSM+) and neither showed pin protrusion, though the pin recession was pretty bad for the price (in the range of 5-7mil).

Fortunately, I haven't seen the same problem with SMA adapters - all of the ones I measured (most of mine come from centricrf and minicircuits) were in spec.

I thought I'd give some further details of my interaction with centricrf, since it seems pretty clear that they're knowingly selling cables out of spec and don't care. I reached out to them with my measurements. They didn't want to refund me. In some sense that's understanble, since these cables were all purchased long enough ago to be out of warranty. But, it doesn't change the fact that they're claiming accordance to a spec they're not meeting. Additionally, the CEO (Bob Hawkins) provided a lot of bogus excuses for my measurements. Even though I mentioned that some of these cables were only mated 10 or so times, he said the problem was wear and SMA cable assemblies should only be used once in an application and then left as is. Such an explanation might be applicable to formable cables (though not to the connectors), but these are a very flexible 086 diameter cable with a low min bend radius (ie not formable cables). If these aren't meant to be flexed and mated/demated, what is? Also, if this were true, why would cable mount connectors typically be rated to 500 mating cycles? In any event, after I pointed out these problems with their arguments, they agreed to replace the cables. But, the replacements (new cables) also showed pin protrusion. This was confusing to me. Obviously I was going to gage them so why waste time and money sending replacements that I know are bad and can't even use?

Anyway, I hope people can read this post and avoid wasting money like I did with these cables. Some takeaways: (1) don't assume because you buy an SMA cable assembly from digikey/mouser or a reputable manufacturer that it's to spec, (2) if you do buy cables like these, gage them on receipt so you can send them back for a refund or replacement in case of issue (i wasted quite a bit of money on these). My plan for simple SMA/BNC/N/etc patch cables is not to buy these anymore but to make them myself. This takes a bit of investment in equipment, but I think is worth it. When I need higher performance cables, I buy high quality (eg gore phaseflex, H+S sucoflex) 2nd hand. If you're patient, you can find some reasonable deals.

[KE5FX]

That is not good to hear, re: Mini-Circuits.  We use a LOT of their 086 hand-flex cables.

[joeqsmith]

I wish there was a database available covering a wide selection of cables and adapters. 

I looked around to see if there were any videos about how to properly gage connectors.  With as user dependent as these measurements are I was expecting to find some training videos from Maury, but there doesn't seem to be much out there.   R&S has a basic connector care video that mentions gageing, but nothing in-depth.   Signal Path had a video on cables but skimming it, never appears to gage anything.

Not trying to damage your ego but I assume that you are using the correct gage and master for the connectors you are testing.  Maybe verified these bad cables with a different operator and gage set before posting?  Had you made a video of the entire process, I would have watched it.  Maybe consider putting something out. 

[matthuszagh]

That's ok - ego not damaged.

I did use two different gage kits for these measurements and that information was in the original post, though I understand how that could have been missed within the large block of text. I used both the Maury A027 SMA push-on gages and the (much more accurate) 3.5mm thread-on gages from an HP 85052B calibration kit. Both of my gages are designed to measure pin protrusion/recession. I do not have the Maury kit to measure dielectric protrusion/recession and (of course) this would not be applicable for 3.5mm connectors. I would like to be able to measure dielectric recession. However, based on the way SMA connectors are attached to cables, the position of the dielectric is already fixed and I expect dielectric protrusion is therefore less likely. Additionally, this is just a guess but since the dielectric is directly adjacent to the reference plane, I expect you might actually be able to determine recession or protrusion by slowly sweeping something with a fine point over the boundary (of course, be careful of scratching the reference plane). I've never tried that though.

Push-on gages are quick and convenient, but there is some play in the mating and so there is some change in the reading depending on how you tilt the gage and SMA connector relative to one another. In my experience this typically results in a range of about 1.5 mil or so. The manual says to engage the connector straight on. However, when the center pin of a connector is nearly aligned the reference plane but initially in recession, and I'm able to get it into protrusion by tilting the mating with the gage, I often find that checking the connector on the thread-on gage shows that it is indeed slightly in protrusion. If a reading is far from a specification boundary and you don't care what the actual reading is (just that it's in spec) this is good enough. If it's close, I then also use the thread-on gage and decide based on that. The manual for the HP 85052B says to perform 3 readings as well as other things like tapping the gage to get it to settle, but in my experience this gage is very repeatable and those things barely affect the reading.

To more directly address your concerns. I checked that the readings from the two gages were consistent (at least to within the range of play from the push-on gage) on a number of different connectors and I used the correct master setting gage (and this is obvious).

As for instructions of use, the manuals are sufficiently detailed in my opinion. I've attached both, in case you want to peruse. If you still think it would be useful I can investigate making a video, but I'm not too experienced with doing this.

[joeqsmith]

I wondered if these cables you measure have a stepped contact?  You stated you have A027 so I assume you have the FP and MP gages with the A027T1 master.  But not the MC gage and A027T2 mater.   If you use the MP gage on a stepless contact, does the gage measure from the dielectric? 

I had read about the other gage set but it seemed that you were doing the work.  This is why I asked if you had an independent person verify your results with a different gage set,  prior to making anything public. 

Did you return the suspect cables?  If so, did they measure them in-house and report back?   Just curious. 

[mark432]

"I wish there was a database available covering a wide selection of cables and adapters. "

Take a look at MIL-STD-348.
That has your key interface dimensions for 90% of common connectors.
http://everyspec.com/MIL-STD/MIL-STD-0300-0499/MIL-STD-348A_420/

There are also "precision" grades of some of those connectors, but you'll know if you have them because you paid 10X normal.
They might take a spec that is typically 20 mils tolerance and bring it down to 2 mils.

Improper pin depth is an easy problem to run into.  I've even seen it happen from thermal cycling.  (With cheap connectors)

[joeqsmith]

"I wish there was a database available covering a wide selection of cables and adapters. "

Take a look at MIL-STD-348.
That has your key interface dimensions for 90% of common connectors.
http://everyspec.com/MIL-STD/MIL-STD-0300-0499/MIL-STD-348A_420/

There are also "precision" grades of some of those connectors, but you'll know if you have them because you paid 10X normal.
They might take a spec that is typically 20 mils tolerance and bring it down to 2 mils.

Improper pin depth is an easy problem to run into.  I've even seen it happen from thermal cycling.  (With cheap connectors)

I don't think I stated that well.  I would be interested in database of cables where independent measurements were made and published. 

[matthuszagh]

I wondered if these cables you measure have a stepped contact?  You stated you have A027 so I assume you have the FP and MP gages with the A027T1 master.  But not the MC gage and A027T2 mater.   If you use the MP gage on a stepless contact, does the gage measure from the dielectric? 

I had read about the other gage set but it seemed that you were doing the work.  This is why I asked if you had an independent person verify your results with a different gage set,  prior to making anything public. 

Did you return the suspect cables?  If so, did they measure them in-house and report back?   Just curious.

The connectors I measured all have a stepped contact and that's what the A027 kit is designed to measure.

I'm the only one who performed these measurements. But, in addition to the fact that the procedure is fairly straightforward, I received a number of independent results that indicate I performed this correctly. These were all listed in the original post, but to reiterate some of them: (1) agreement between both gages, (2) all high quality Gore phaseflex and H+S sucoflex cables I have met the tighter 0 to 3 mil center pin recession requirement, (3) all adapters with an SMA male connector measured within the 0 to 10 mil pin recession requirement (and I probably have like 20 adapters or so).

Also, it seems pretty clear the company never gaged the center pin on these cables. They reported several dielectric recession measurements they had on file but never gave me any pin recession measurements. They never admitted not having gaged the center pins but never actually denied it either. But to your question, even when they sent me replacement cables (some of which ended up being bad), they never provided me measurements of those either. And no I never got a refund. I was out of warranty and they seemed pretty pissed at me that I was making any sort of a fuss about this (apparently, I should pay $1000 for each cable if I want this, or something like that). This whole thing was made more difficult by the fact that I was well out of warranty for all of these. I reached out to digikey too about the crystek cable and they just told me it was out of warranty and did not seem concerned about the pin protrusion (even though I used that cable probably just once and the protrusion was not due to wear).

I think it's pretty unlikely measurement error is the problem here. I have a hard time coming up with a self-consistent explanation of how that might work.

It seems more likely the mentioned companies (and probably others) don't bother to gage their cheaper cable assemblies and no one is checking them on it. Or, if they do, clients complain and the company sends replacements but doesn't bother to change the process. It's probably cheaper to send the occasional replacement cable than to improve the process and validate cables more thoroughly before selling them. Who cares about being honest, apparently. The aerospace company I work for buys mini-circuits cables, but doesn't gage them. I expect we're not the only ones. That's just a guess of course. But, how many people gage $40 cables? I imagine most of the people gaging cables are in a higher precision metrology-type setting and buying much more expensive cables.

I feel ok with the fact that I didn't seek a second opinion before outing these companies. But, I have the bad cables here and if someone wants to pay for one to be shipped to them to gage it (if they have the capabilities to do so) I'd probably agree to that.

[joeqsmith]

...all have a stepped contact...

Have you ran into stepless contacts with any of your cables? 

Below, I assume part number of the cable followed by two measurements.  MP , MS gage? Just two measurement with same gage?  The Maury vs HP gage?  What ever these are, is it a single measurement or did you take say five measurements, then averaged?  Just curious of the technique you are using.  Maybe these two number are the max min of 10 readings for each cable?

C589-086-48: -0.5, +2.0
C589-086-12: -1.5, +2.0
C589-086-36B: -1.0, +2.0
C589-086-36B: -3.0, 0.0
C589-086-60: -2.0, -2.0
C589-086-72: -1.0, -1.0

[joeqsmith]

I tried a search to get some context and it seems like gageing connectors may be new to you.   

https://www.eevblog.com/forum/testgear/pin-protrusion-in-commercial-sma-cable-assemblies/
https://www.eevblog.com/forum/repair/how-to-clean-an-sma-gage-kit/
https://www.eevblog.com/forum/metrology/difference-between-push-on-and-thread-on-microwave-connector-gages/


I'm sure you have dug into all of this before dragging these companies through the mud, and not knowing exactly what you are doing,  I am left with questions....

Your MP gage measures from the outer conductor mating plane to the flat surface of the step? 

Today there are wide variations in the SMA designs. I categorize them as the "stepped", "stepless" and  "angled". 

If the step is not a flat surface, the reading will depend in the gage bore and where it touches off on the angle of the step? 

Does the MC gage measure from the outer conductor to the tip of the pin?  Avoiding the variations in the step or angled step?   

Looking at some cables I have, their construction is all over the place.  You have never shown any photos of the pin style used in the cables you tested.     

I could not locate a mechanical drawing for the MP gage.  I assume you contacted Maury about which gage would be suitable for the connectors you are trying to measure.   What are the disadvantages of using the MC gage? 

I also found this 25 year old application note from Maury Microwave that talks about the SMA and 3.5mm.   

While I was not able to locate any decent best practices manuals on proper measurement techniques of RF connectors, it is a mechanical measurement.  I did find a good machinist's manual.  It covers the basics of temperature, storage, cleaning, use of the master gages.... 

[matthuszagh]

Have you ran into stepless contacts with any of your cables? 

No, all of my cables have a stepped center contact. In fact, I'm not even sure I've ever actually seen a stepless center contact, though I was aware of their existence. In any event, stepped center contacts seem to be much more common.

Below, I assume part number of the cable followed by two measurements.  MP , MS gage? Just two measurement with same gage?  The Maury vs HP gage?  What ever these are, is it a single measurement or did you take say five measurements, then averaged?  Just curious of the technique you are using.  Maybe these two number are the max min of 10 readings for each cable?

C589-086-48: -0.5, +2.0
C589-086-12: -1.5, +2.0
C589-086-36B: -1.0, +2.0
C589-086-36B: -3.0, 0.0
C589-086-60: -2.0, -2.0
C589-086-72: -1.0, -1.0

Each cable assembly has two connectors. The list above gives one measurement result for each connector of the assembly.

[matthuszagh]

I tried a search to get some context and it seems like gageing connectors may be new to you.   

https://www.eevblog.com/forum/testgear/pin-protrusion-in-commercial-sma-cable-assemblies/
https://www.eevblog.com/forum/repair/how-to-clean-an-sma-gage-kit/
https://www.eevblog.com/forum/metrology/difference-between-push-on-and-thread-on-microwave-connector-gages/

The first link is basically a duplicate of this thread. I was trying to determine if other people had also found pin protrusion to be very common.

The 2nd link is from a gage kit I ended up returning because I didn't feel that I would be able to clean it properly such that I could achieve reliable results. The kit I have has no such degraded foam on the mating surfaces to remove, since both gages and the gage master were protected by plastic coverings.

The 3rd link is from over 2 years ago and the answer posted there is in agreement with what I've seen having both types of gages.

Your MP gage measures from the outer conductor mating plane to the flat surface of the step?

Correct.

Today there are wide variations in the SMA designs. I categorize them as the "stepped", "stepless" and  "angled". 

If the step is not a flat surface, the reading will depend in the gage bore and where it touches off on the angle of the step? 

As mentioned all of the connectors I gaged are of the stepped variety. I was not aware of angled steps. Can you provide some further information about this? In any event, both the centricrf and mini-circuits cables state conformance to MIL-STD-348 in their respective datasheets. Unless I've missed something, that standard only permits for male SMA connectors with a flat stepped contact and with no contact, but not stepless or angled steps. Also, they don't look like angled steps, though if the angle grade were small I suppose it's possible I wouldn't be able to determine this by sight. But, all SMA connector variants need to be mechanically-compatible with all other SMA connectors as well as 3.5 mm and 2.92 mm connectors. Unless I'm mistaken, this does not allow for pin protrusion on any part of an angled step. So, measuring pin protrusion on an angled step would still indicate a non-comforming connector. Still, unless you can provide standards to explain this angled step variant (and even the stepless variant), these sound like non-standard configurations. Again, the companies I mentioned claim adherence to MIL-348.

Does the MC gage measure from the outer conductor to the tip of the pin?  Avoiding the variations in the step or angled step?   

I don't know. I don't have an MC gage and have never used one.

Looking at some cables I have, their construction is all over the place.  You have never shown any photos of the pin style used in the cables you tested.     

That may be true for your cable assemblies, but not for mine. All of my SMA connectors on cable assemblies and adapters are stepped and as far as I can tell are not angled.

I provided part numbers and you can probably find photos from that. Anyway they're stepped, do I really need to provide you with photos?

I could not locate a mechanical drawing for the MP gage.  I assume you contacted Maury about which gage would be suitable for the connectors you are trying to measure.   What are the disadvantages of using the MC gage? 

The MC gage is designed for a stepless center contact, whereas the MP gage is designed for a stepped center contact. This is all clearly stated in the A027 manual. What precisely do you want me to ask of Maury? It seems like all the necessary information is already available in the manual.

I also found this 25 year old application note from Maury Microwave that talks about the SMA and 3.5mm.   

While I was not able to locate any decent best practices manuals on proper measurement techniques of RF connectors, it is a mechanical measurement.  I did find a good machinist's manual.  It covers the basics of temperature, storage, cleaning, use of the master gages....

I appreciate these resources.

I have trouble believing temperature can account for the 5 mil in protrusion I've measured on some connectors. The datasheets for the mini-circuits and centricrf cables state an operating temperature range of -55C to 105/125C. Moreover, MIL-348 does not state a temperature at which the mechanical requirements apply, as far as I can tell. I believe that means that the connectors must adhere to the stated mechanical specifications over the provided operating temperature range. I performed these measurements in a room kept at normal room temperature. If they're not designed to have the correct mechanical specifications at room temperature, at what temperature do you think they are supposed to be correct?

I'm in general happy to continue this discussion, and you've provided some useful resources, which I appreciate. However, I don't appreciate the implications that I've unjustifiably sullied the good names of companies. If you're not convinced that's your prerogative, but I think the evidence seems pretty clear. I followed the manuals for my gages, used the gages on connectors for which they were designed, and checked the measurements on a second gage set before "I dragged names through the mud". But, no, I didn't pay NIST to ensure all my measurements were accurate to within fractions of a micron before I posted this. I don't think that's necessary. Anyway, I think my claims are justified. I created this post to help people who do not have gage capabilities. You're free to believe whatever you'd like.

[joeqsmith]

Today there are wide variations in the SMA designs. I categorize them as the "stepped", "stepless" and  "angled". 

If the step is not a flat surface, the reading will depend in the gage bore and where it touches off on the angle of the step? 

As mentioned all of the connectors I gaged are of the stepped variety. I was not aware of angled steps. Can you provide some further information about this? In any event, both the centricrf and mini-circuits cables state conformance to MIL-STD-348 in their respective datasheets. Unless I've missed something, that standard only permits for male SMA connectors with a flat stepped contact and with no contact, but not stepless or angled steps. Also, they don't look like angled steps, though if the angle grade were small I suppose it's possible I wouldn't be able to determine this by sight. But, all SMA connector variants need to be mechanically-compatible with all other SMA connectors as well as 3.5 mm and 2.92 mm connectors. Unless I'm mistaken, this does not allow for pin protrusion on any part of an angled step. So, measuring pin protrusion on an angled step would still indicate a non-comforming connector. Still, unless you can provide standards to explain this angled step variant (and even the stepless variant), these sound like non-standard configurations. Again, the companies I mentioned claim adherence to MIL-348.

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.   

*** RevB
https://landandmaritimeapps.dla.mil/Downloads/MilSpec/Docs/MIL-STD-348/std348.pdf
***

Looking at some cables I have, their construction is all over the place.  You have never shown any photos of the pin style used in the cables you tested.     

That may be true for your cable assemblies, but not for mine. All of my SMA connectors on cable assemblies and adapters are stepped and as far as I can tell are not angled.

I provided part numbers and you can probably find photos from that. Anyway they're stepped, do I really need to provide you with photos?

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.

I could not locate a mechanical drawing for the MP gage.  I assume you contacted Maury about which gage would be suitable for the connectors you are trying to measure.   What are the disadvantages of using the MC gage? 

The MC gage is designed for a stepless center contact, whereas the MP gage is designed for a stepped center contact. This is all clearly stated in the A027 manual. What precisely do you want me to ask of Maury? It seems like all the necessary information is already available in the manual.

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?

I appreciate these resources.

I have trouble believing temperature can account for the 5 mil in protrusion I've measured on some connectors. The datasheets for the mini-circuits and centricrf cables state an operating temperature range of -55C to 105/125C. Moreover, MIL-348 does not state a temperature at which the mechanical requirements apply, as far as I can tell. I believe that means that the connectors must adhere to the stated mechanical specifications over the provided operating temperature range. I performed these measurements in a room kept at normal room temperature. If they're not designed to have the correct mechanical specifications at room temperature, at what temperature do you think they are supposed to be correct?

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. 

I'm in general happy to continue this discussion, and you've provided some useful resources, which I appreciate. However, I don't appreciate the implications that I've unjustifiably sullied the good names of companies. If you're not convinced that's your prerogative, but I think the evidence seems pretty clear. I followed the manuals for my gages, used the gages on connectors for which they were designed, and checked the measurements on a second gage set before "I dragged names through the mud". But, no, I didn't pay NIST to ensure all my measurements were accurate to within fractions of a micron before I posted this. I don't think that's necessary. Anyway, I think my claims are justified. I created this post to help people who do not have gage capabilities. You're free to believe whatever you'd like.

I tend to be data driven.  Beliefs and feelings go out the window.    You ran the tests and made the results public.  I am just asking what I considered some basic questions as I assumed you had dug into this rabbit hole.     

[joeqsmith]

Johnson® Stainless Steel SMA Connectors meet or exceed the performance requirements of MIL-PRF-39012.  All designs are based on 50 ohm system impedance per MIL-STD-348, and operate at frequencies up to 26.5 GHz

Straight Solder Type Plug - without Contact, Thread-on Nut
Connector Interface for .141 Cable

Obviously, no step but does it actually conform to MIL-STD-348? 

https://www.mouser.com/datasheet/2/643/pi-CCS-JOHN-141-0701-612-1290055.pdf

[joeqsmith]

Document showing their semi-rigid connector.  No step but appear to conform.   
https://www.mouser.com/datasheet/2/643/pi-CCS-JOHN-142-0593-421-1290159.pdf

Does the standard require that the connectors have a step, or that they mate with the drawings shown?   I have no idea, which is why I am asking.   

[Smoky]

If it hasn't been mentioned before, I saved this article a while back about making SMA cables. It explains the assembly of semi-rigid cables with good pictures using the proper tools.

The author mentions that a quick-check that the shoulder of the center contact should be flush with connector's dielectric when looking into the business end when it's finished as an indication of a proper assembly.

[Smoky]

 Even though I mentioned that some of these cables were only mated 10 or so times, he said the problem was wear and SMA cable assemblies should only be used once in an application and then left as is.
 

I've been reading the many responses and watching the videos that joeqsmith has linked to his SMA/VNA topics.

He mentions one or more times not to allow the center contact to spin when tightening the coupling nut.

I think that this action is the most important to avoid. How many twists of the center contact will eventually remove the plating from the mating connector 

Now imagine that the center contact is protruding at the same time.

It could be possible that the best connection that the SMA plug ever makes is the first one.

[shabaz]

Unfortunately I'm speculating here, but it seems a bit much to expect these cables to remain at the correct pin depth.
Those flexible 0.086" cables re-purpose RG-405 semi-rigid connectors from what I can tell (at least, that's what I intend to do; I have purchased some RG-405 connectors for that purpose, but need to obtain a solder bath/pot (needed to semi-rigid-ize the cable on the end). The pin depth is set at time of assembly with some of those SMA connectors, i.e. seems a friction fit. As someone who knows nothing in this area, I'm curious, could the pin maybe move slightly when using the cable, maybe if the coax bends many times? Or have enough space for movement when the connector is inserted/removed many times?

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.

Another option of course is right-angle SMA connectors, since they will have the pin depth permanently fixed.

I've never measured SMA connectors, I don't have any critical requirements for that, and use adapters on my most expensive equipment, so I have never investigated this topic deeper unfortunately, but am interested in this thread.

[Smoky]

Full disclosure, I am a total newb when it comes to SMA cables and I've never had a use for one before, but, and thanks to the sale that went on at Arrow over the past year, I own about 150 SMA cables now so, at the least, I describe myself currently as a serious collector

The pin depth is set at time of assembly with some of those SMA connectors, i.e. seems a friction fit. As someone who knows nothing in this area, I'm curious, could the pin maybe move slightly when using the cable, maybe if the coax bends many times? Or have enough space for movement when the connector is inserted/removed many times?

I have a few of the Amphenol .047/.085/.141 semi-rigid cables with "friction-fit" connectors as you describe. Since the body of the connector is soldered to the tin-soaked outer braid I can't imagine it stretching or compressing all that much to where it would affect the center contact. From what I've read, semi-rigid, hand formable, etc., types are not to be bent within a couple inches of the connector. Yet there are super-flexible variants that can be bent at a right angle directly after the fitting.

As for the "friction-fit", my guess is that galling takes effect on the gold or silver plating that lines the mating surfaces when it gets pushed in and helps to maintain a good contact even with slight movement

[matthuszagh]

I'm in general happy to continue this discussion, and you've provided some useful resources, which I appreciate. However, I don't appreciate the implications that I've unjustifiably sullied the good names of companies. If you're not convinced that's your prerogative, but I think the evidence seems pretty clear. I followed the manuals for my gages, used the gages on connectors for which they were designed, and checked the measurements on a second gage set before "I dragged names through the mud". But, no, I didn't pay NIST to ensure all my measurements were accurate to within fractions of a micron before I posted this. I don't think that's necessary. Anyway, I think my claims are justified. I created this post to help people who do not have gage capabilities. You're free to believe whatever you'd like.

I tend to be data driven.  Beliefs and feelings go out the window.    You ran the tests and made the results public.  I am just asking what I considered some basic questions as I assumed you had dug into this rabbit hole.     

Fair enough. 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 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.

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.

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.

[matthuszagh]

Obviously, no step but does it actually conform to MIL-STD-348? 

https://www.mouser.com/datasheet/2/643/pi-CCS-JOHN-141-0701-612-1290055.pdf

Also referencing your other, related post.

Yeah it's a valid question. It's hard for me to understand how this adheres to -348 since -348 clearly shows a flat step. Now I suppose they could interpret -348 as saying there cannot be a step that is in protrusion, in which case no step would meet this spec and an angled step would meet this spec too as long as no part of the step passes the reference plane. That's just a guess though. If that's what people are doing, it still seems like a bit of a stretch to claim adherence to the spec. Or maybe the spec should acknowledge these variants and clarify what qualifies as adherence in these cases.

[matthuszagh]

He mentions one or more times not to allow the center contact to spin when tightening the coupling nut.

Yep, and this is critical for basically all coaxial connectors. The body should not rotate, only the coupling nut should rotate. Failure to adhere to this can definitely wear out mating surfaces. That's not my issue though, as I've known this for a long time and am quite careful.

[shabaz]

I own about 150 SMA cables now

Wow, nice! I've not encountered such a good deal, but have slowly acquired a fair few (nowhere near 150 currently!). I used to use SMB a lot more (because that was the main "mid-size" RF connector that was used at my workplace for a while; internal to equipment) but pretty much stick to SMA these days.

I believe/hope you'll find them extremely useful; they are a very friendly size to work with when prototyping, compared to the more bulky BNC, for instance, plus the sockets are very low-cost for quickly making connections onto a prototype. (Some very low-cost SMA sockets are available at LCSC; they are not top quality at that price, but they are great for general prototyping).

I've been meaning to write a sort of "SMA connectors: How to make use of them" blog for ages since they are great problem-solvers, and a friend suggested it would be useful since not everyone comes across that connector in their lines of work) Unfortunately, I have not gotten around to it so far. The main negative is that it can sometimes be awkward to build up a cable (since tools may be needed), but since you've got ready-made cables, that issue is gone! I, too, try to use ready-made cables if possible but end up occasionally DIY'ing some.

[Smoky]

Shabaz, here's one group of 5 cables I bought on sale from Arrow. These are 24" Amphenol ATC Phase Stable SMA cables (095-902-466-001):



They cost ~$28 each but their regular price is ~$200 each now!



This I think is Amphenols first generation of this cable (dtd 2017) because it used the original manufacturer Harbour strip-braid cable (SB142). Amphenol uses Times Microwave cable now. Even the drawing/datasheet is dated 2017. Arrow had a lot of old inventory on sale:



Get a load of this Matthuszagh, you mentioned a durability of 500 cycles for SMA cables. The datasheet reads that these ATC cables are rated for 5000 cycles... minimum



Look at the design requirements of this cable. One rating states VSWR of 1.27:1 is the max up to 20GHz.

You're not just getting a cable made with expensive parts, you're getting a cable that's fully tested too

[joeqsmith]

If it hasn't been mentioned before, I saved this article a while back about making SMA cables. It explains the assembly of semi-rigid cables with good pictures using the proper tools.

The author mentions that a quick-check that the shoulder of the center contact should be flush with connector's dielectric when looking into the business end when it's finished as an indication of a proper assembly.

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.

[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.   

[Someone]

Like I said, math or GTFO.

The math is not that complicated.
Start with a simple beam fixed at one end on the nut, and a load at the other.
The moment along the beam is equal to the torque, maximal at the fixed "nut" end and linearly tapering to 0 at the load.
Given the breaking "click" joint of the torque wrench is not coaxial with the fixed point, it will be breaking at a fraction of the torque imparted at the nut.
If you move the point of the load along the beam while keeping the click joint consistent in position and breaking moment then you get the result found in the video above.

Closer to the nut = higher than anticipated/intended torque.

Maths first year engineering!

[Smoky]

"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."

I was just envisioning a tool that you could palm and imagine it's like a flare nut wrench where still the wrench goes around all corners of the hex but leaves a slot for the cable to slip through.

Some impact sockets have plastic liners so that chrome lugnuts avoid being marred or even softer metals having their corners getting rounded if the wrench slips.

Btw, I was just joking about scratching the nuts, but what the heck, if it can be avoided, why not

[KE5FX]

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.

What's the guy in the photo doing?  Removing, or installing?  I have no beef with the video, only the photo.

[KE5FX]

The math is not that complicated.
Start with a simple beam fixed at one end on the nut, and a load at the other.
The moment along the beam is equal to the torque, maximal at the fixed "nut" end and linearly tapering to 0 at the load.
Given the breaking "click" joint of the torque wrench is not coaxial with the fixed point, it will be breaking at a fraction of the torque imparted at the nut.

If it's "first year engineering," it should be easy to do the math.  What is the actual difference between the torque applied to the fastener at breakover when the wrench is held at the very tip of the handle, and the torque applied when the wrench is held at, say, the halfway point?

Unlabeled graphs might have sufficed at your engineering school, but not at mine.

[Someone]

The math is not that complicated.
Start with a simple beam fixed at one end on the nut, and a load at the other.
The moment along the beam is equal to the torque, maximal at the fixed "nut" end and linearly tapering to 0 at the load.
Given the breaking "click" joint of the torque wrench is not coaxial with the fixed point, it will be breaking at a fraction of the torque imparted at the nut.

If it's "first year engineering," it should be easy to do the math.  What is the actual difference between the torque applied to the fastener at breakover when the wrench is held at the very tip of the handle, and the torque applied when the wrench is held at, say, the halfway point?

Unlabeled graphs might have sufficed at your engineering school, but not at mine.

Unlabelled graph still presents the ratios, unlike your question with zero numerical input.

So you'd like someone to calculate the change in torque for an undefined length, with and undefined change in length, and an undefined relative breaking pivot ? I'm pretty sure the answer is undefined, but we can say the torque is larger when the force/load is at the halfway point compared to the endpoint.

Only if the braking joint distance to the rotating axis of the nut approaches 0 does the torque remain constant. Those ratios are trivial triangles!

[Smoky]

This comment I'm making here has nothing to do with Joeqsmith and KE5FX's conversation.

Torque wrenches should never be used to loosen.

Break-away torque is much higher when loosening.

[KE5FX]

Only if the braking joint distance to the rotating axis of the nut approaches 0 does the torque remain constant. Those ratios are trivial triangles!

The difference isn't zero, it just isn't relevant. 

For that matter, with these low-torque tools, the angle at which the wrench is held is likely more important.  My Fairview Microwave wrench will practically break over by itself if held horizontally by the jaws, as in the video Joe linked.  Not that the wrench should be held horizontally, but if you do, you'll quickly realize the absurdity of worrying about where you hold it.

For this conversation to go any further, I think someone's going to have to buy a scale and rig up a demo with the actual hardware in question.  And come up with a way to correct the results for the wrench's mass distribution and angle at breakover. 

[Someone]

Only if the braking joint distance to the rotating axis of the nut approaches 0 does the torque remain constant. Those ratios are trivial triangles!

The difference isn't zero, it just isn't relevant.

At which point the onus is on you to justify the magnitude of not relevant. With the breaking joint being 20-30% of the way up the shaft (Huber+Suhner or Rohde & Schwarz branded SMA torque wrenches) the change in torque from using the end vs the middle of the "handle" (bit beyond the joint) would be a 20-30% increase using the simple first order geometric approximation of the bending moments (zero thickness shafts etc).

If I've done the algebra correctly that specific case of comparing the load at the end or half way from the end to the breaking joint falls out to a neat linear: increase in torque = breaking joint distance from torque axis as a %

[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.

What's the guy in the photo doing?  Removing, or installing?  I have no beef with the video, only the photo.

Maybe cut back on the eggnog. 

[joeqsmith]

...
Torque wrenches should never be used to loosen.

Break-away torque is much higher when loosening.

While I agree in general, the style wrench mentioned is similar to mine and will hit a dead stop when tightening or loosening.   They offer that same wrench for different sized connectors (which require much higher torque).  The highest I found was factory calibrated at 14 in-lbs.  Looking at that video where I pushed to SMA connectors far beyond their limits, at 35 in-lbs the connectors along with the copper ground plane were tore from the test boards.

[joeqsmith]

For this conversation to go any further, I think someone's going to have to buy a scale and rig up a demo with the actual hardware in question.  And come up with a way to correct the results for the wrench's mass distribution and angle at breakover.

Well?

[nctnico]

Like I said, math or GTFO.

The math is not that complicated.
Start with a simple beam fixed at one end on the nut, and a load at the other.
The moment along the beam is equal to the torque, maximal at the fixed "nut" end and linearly tapering to 0 at the load.
Given the breaking "click" joint of the torque wrench is not coaxial with the fixed point, it will be breaking at a fraction of the torque imparted at the nut.
If you move the point of the load along the beam while keeping the click joint consistent in position and breaking moment then you get the result found in the video above.

Closer to the nut = higher than anticipated/intended torque.

The key is the pivot point for the click mechanism being away from the rotation point of the nut. The error in torque will go up exponentially when the force is applied closer to the pivot point. If the force is applied at the pivot point, the mechanism will never 'click'.

The video joeqsmith linked to in this reply, shows the math:
https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/msg5746497/#msg5746497

IMHO it is worthwhile to teach inexperience engineers the correct way to work with a torque wrench so they will do it right. Instead of assuming people know how to operate a tool. Just look at how many people hold a hammer close to the head instead of using the entire handle.

edit: typo

[KE5FX]

But the difference is immaterial.  It's silly to pretend otherwise, and counterproductive to waste limited bandwidth between instructors and students by telling the students silly things.

If I weren't speaking from experience, I wouldn't speak at all.

[joeqsmith]

The discussion is similar to dealing with the believers in free energy, warp drives, all things Tesla, robots made with string and old socks with AI.  Hams seem to follow a rich history of deep rooted beliefs based on folklore.  I dedicated a thread to the Bird Wattmeter being the gold standard of accuracy for the hams. 

[nctnico]

I wouldn't go that far. But I do believe that people should be instructed properly. Sometimes to the point where you might think something is too commonly known to need explaination. But that is a trap for old players 

I'm more and more involved in bigger projects with bigger teams which includes coaching / teaching junior engineers. One of the things I realised quickly is how much knowledge I take for granted. I'm not somebody who is going around labelling people silly or stupid though. If somebody under my supervision is doing something wrong which I didn't explain (well enough) then that is my fault. A long time ago an intern at a former employer managed to put a PCI express card into an AGP slot (or the other way around -doesn't matter-) as part of putting a computer together. As a computer savy 'crowd' we all found that a silly mistake. But in hindsight the fault was on the person supervising the intern.

[Someone]

Like I said, math or GTFO.

The math is not that complicated.
Start with a simple beam fixed at one end on the nut, and a load at the other.
The moment along the beam is equal to the torque, maximal at the fixed "nut" end and linearly tapering to 0 at the load.
Given the breaking "click" joint of the torque wrench is not coaxial with the fixed point, it will be breaking at a fraction of the torque imparted at the nut.
If you move the point of the load along the beam while keeping the click joint consistent in position and breaking moment then you get the result found in the video above.

Closer to the nut = higher than anticipated/intended torque.

The key is the pivot point for the click mechanism being away from the rotation point of the nut. The error in torque will go up exponentially when the force is applied closer to the pivot point. If the force is applied at the pivot point, the mechanism will never 'click'.

The video joeqsmith linked to in this reply, shows the math:
https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/msg5746497/#msg5746497

So why reply to that message? A big pile of furious agreement with what I said? It was KE5FX asking for a worked example.

[Someone]

But the difference is immaterial.

How can you justify the difference being irrelevant/immaterial? If a torque wrench has a 10% tolerance, and where you press on it adds another 30%, while the specification for the joint is +/- 33% then you've failed to meet the requirements.

[KE5FX]

But the difference is immaterial.

How can you justify the difference being irrelevant/immaterial? If a torque wrench has a 10% tolerance, and where you press on it adds another 30%, while the specification for the joint is +/- 33% then you've failed to meet the requirements.

If holding the torque wrench halfway up the handle adds 30% torque, the problem isn't where you're holding it.  The problem is that you bought a really crappy torque wrench.

[nctnico]

But the difference is immaterial.

How can you justify the difference being irrelevant/immaterial? If a torque wrench has a 10% tolerance, and where you press on it adds another 30%, while the specification for the joint is +/- 33% then you've failed to meet the requirements.

If holding the torque wrench halfway up the handle adds 30% torque, the problem isn't where you're holding it.  The problem is that you bought a really crappy torque wrench.

Looking at the R&S torque wrenches & sizes: https://scdn.rohde-schwarz.com/ur/pws/dl_downloads/pdm/cl_brochures_and_datasheets/specifications/3607_1994_22/ZN-ZTW_dat-sw_en_3607-1994-22_v0300.pdf

And going by the formula given in the video, applying force to an R&S torque wrench (the f R&S®ZN-ZTW model .10 on page 6) at 1/3 of the handle instead of the specified load point, gives an error of over 50%. Pushing it at half way the handle, the error is over 20% already. This while the accuracy of the torque wrench itself is specified at 2.25%. The bottom line is, if you want to use these torque wrenches within their specification -if that is important-, you have to apply the force exactly at the specified load point. Even deviating 1.5cm from the load point gives an error of 3%.

[KE5FX]

https://youtu.be/NVE_ztptYPY

TL,DW: Hold the wrench like a sane human being and it will be fine.  No, really.  It will be fine.

I was able to overtorque to ~12-13 in-lbs by tying a wire just below the halfway point and pulling on it (not shown, done on a different bench), so I can't support my original blanket assertion ("the breakover point is independent of (the handle's) leverage.")  Frankly, it feels more like plain old stiction than mechanical action because the result was so inconsistent -- in one trial it took more than 20 in-lbs to break over, which makes no sense mathematically -- but I will let Joe have that hill.  There are various other ways to do the same thing, all of which involve pulling or pushing the handle in odd directions. 

But unless you are just trying to break something, the handle exists for a reason and can be used as such.  There's no reason to hold it by the tip of the handle, or to instruct anyone else to do so.

[G0HZU]

To help try and resolve this issue, I waited until I was back at work today. There is a suite of Gedore torque testers there and I selected the 0.5 to 5 Nm model. It looks like a bigger and more expensive version of the one linked to below:

https://www.gedore.com/en-de/products/torque-tools/torque,-measuring-testing-appliances/torque-testing-appliances/capture-hub/ch-5---3124053

I did try and remember the model number but I've forgotten it. The datasheet said 0.5% accuracy across most of the range. It measures and holds the display at the peak torque achieved at the break point of the torque tool under test.

I tested three Agilent 8710-1765 torque tools taken from 85033E VNA cal kits. I held them the same way as recommended by my N4431B-60006  Ecal module manual as seen on page 4-19 here:

https://www.keysight.com/gb/en/assets/9018-03493/reference-guides/9018-03493.pdf?success=true

This means holding it between finger and thumb at the tip of the tool.

When I do this, I get really repeatable results each time. There is a slight difference between each torque tool but not much. When tested, they ranged from 0.897Nm to 0.917 Nm but probably none of them have been adjusted in many years.

In terms of repeatability, I could typically achieve better than +/- 0.01 Nm if I really tried to hold and rotate the torque tool in exactly the same way. This was quite impressive. I also saw about a 0.025 Nm difference if I reversed the tool as the hex cutout is at an angle.

If I then tried the same at halfway down the gold handle of the 8710-1765 then the reported torque was at about 1.07 Nm. If I tried at most of the way down the handle (where it says 0.9 Nm) then the torque went up to about 1.3 Nm.  However, it's unlikely anyone would use the tool like this.

If I held it the way most people would hold it fairly near the tip using several fingers and thumb (as shown as the 'wrong' way to hold it in that guide doc) then I couldn't get repeatable results. A lot depends on how the fingers or thumb apply the pressure. I could see anything from 1.0 Nm to 0.8 Nm. Usually it showed 0.85 Nm to 0.95 Nm which is quite close to the 0.9 Nm spec for this torque wrench.

I did also notice that if I held the torque tool like a golf club with my thumb along the shaft and several fingers wrapped around it, the breaking torque could sometimes go below 0.75 Nm.

So in summary, if you are a nerd and you really do want to achieve repeatable torque settings that are impressively close to 0.9 Nm then hold it at the tip between finger and thumb as recommended by Keysight.

However, if you are an engineer just doing everyday SOLT calibrations with a sub 8.5 GHz VNA then I don't see a problem holding it the 'wrong' way because the error in the torque isn't that significant in my opinion.

[Smoky]

G0HZU, if you have the time, please try this.

Tighten the nut of an SMA connector onto a fitting with a torque wrench to its proper torque.

Next, make a mark on the fitting where one of the corners of the nut is located (mark the corner of the nut too).

Now back the nut off 1/4 turn or so until it's slightly loose.

Then tighten the nut back with just your fingers and see how close you can get to the mark on the nut to line up with the mark on the fitting.

I have no idea what to expect but was just wondering what finger-tight is

[G0HZU]

G0HZU, if you have the time, please try this.

Tighten the nut of an SMA connector onto a fitting with a torque wrench to its proper torque.

Next, make a mark on the fitting where one of the corners of the nut is located (mark the corner of the nut too).

Now back the nut off 1/4 turn or so until it's slightly loose.

Then tighten the nut back with just your fingers and see how close you can get to the mark on the nut to line up with the mark on the fitting.

I have no idea what to expect but was just wondering what finger-tight is

I think I can try this at work with the torque tester. It's this model here:

https://gedoregroup.ir/wp-content/uploads/P30390-ET-Cal-Compact-Instructions-PDF-Aug-2011.pdf

It's the ET-cal-5  0.5 Nm to 5 Nm model. There's a load of adaptors that plug into it including one for SMA sized fixtures.

I also tried a classic Huber and Suhner SMA torque tool Z-0-0-21 on it yesterday. These are spec'd at 1Nm. 


https://www.farnell.com/datasheets/3157770.pdf


I was getting bored by the time I tested this one, but it read 0.9 Nm when held with just thumb and finger at the sticker at the end. This was quite repeatable but not quite as repeatable as the Keysight torque tool.

When held half way down the silver handle with thumb and finger the torque went up to about 1.3 Nm. I don't think many people would use it like this because it is not as easy to use it this way and it isn't a natural way to hold the tool.

I could reach 1.6Nm if I went closer to the pivot point. This really wasn't pleasant to do with just finger and thumb so I don't think this is a realistic test.

If used fairly casually near the tip using thumb and a couple of fingers (the way I usually use it) the torque varied from about 0.85Nm to about 1.05 Nm.

The golf club grip brought the break point down to below 0.75 Nm.

It was typically about 1 Nm though when used the way most people would use it. This is good enough for the majority of VNA based applications.

The Suhner tool definitely can't match the Keysight tool for repeatability and the torque break point is 1 Nm rather than 0.9 Nm. I'm not sure this matters much though...


Maybe if someone was doing a metrology grade comparison between calibration kits up at many GHz it might be worthwhile to swap across to the Keysight tool (and use the Keysight method) to achieve a repeatable torque throughout the SOLT process.

However, for everyday VNA stuff I'm happy to carry on using the little Suhner tool across a spread of about 0.85 Nm to 1.05Nm when held casually near the end using two or three fingers and a thumb.

[joeqsmith]

https://youtu.be/NVE_ztptYPY

TL,DW: Hold the wrench like a sane human being and it will be fine.  No, really.  It will be fine.   I was able to overtorque to ~12-13 in-lbs by tying a wire just below the halfway point and pulling on it (not shown, done on a different bench), so I can't support my original blanket assertion ("the breakover point is independent of (the handle's) leverage.")  Frankly, it feels more like plain old stiction than mechanical action because the result was so inconsistent -- in one trial it took more than 20 in-lbs to break over, which makes no sense mathematically -- but I will let Joe have that hill.  There are various other ways to do the same thing, all of which involve pulling or pushing the handle in odd directions. 

But unless you are just trying to break something, the handle exists for a reason and can be used as such.  There's no reason to hold it by the tip of the handle, or to instruct anyone else to do so.

A sane person follows the manufactures procedures. 

I was expecting  you to follow their instructions below, but you would need to ditch the cheap torque meter for a peak reading meter.   Of course, the absolute values are meaningless but at least you could get some relative data.    Then, don't cover up the handle with your hand as you show.  Maybe just use a finger and work your way up the handle in one inch increments. 

• To improve performance of a wrench that hasn’t been used recently, actu-
ate the wrench by clicking the wrench head back and forth several times
before use. This will spread the lubricant through the internal mechanism.
• Click type tools require smooth consistent application of force. Each torqu-
ing action should be completed within 2 seconds. Slower or faster torquing
action will detract from accuracy.


***
Maybe measure at six locations.   You did later state anywhere on the red handle, but with the 3 closer to the pivot point, I expect you will measure a big increase.  While you asked about where the pivot point was for your wrench, I think once you place your finger in the far left location and apply force, you will have answered that one for yourself.

[joeqsmith]

To help try and resolve this issue, I waited until I was back at work today.   ....

Does your company have a set of gages to repeat the OPs measurements?   Or, I wonder if you or your company has seen a similar trend? 

***
I'm curious if your company produces any products that use RF connectors during testing, and it so do they torque them?

[KE5FX]

A sane person follows the manufactures procedures. 

I was expecting  you to follow their instructions below, but you would need to ditch the cheap torque meter for a peak reading meter.   Of course, the absolute values are meaningless but at least you could get some relative data.    Then, don't cover up the handle with your hand as you show.  Maybe just use a finger and work your way up the handle in one inch increments. 

• To improve performance of a wrench that hasn’t been used recently, actu-
ate the wrench by clicking the wrench head back and forth several times
before use. This will spread the lubricant through the internal mechanism.
• Click type tools require smooth consistent application of force. Each torqu-
ing action should be completed within 2 seconds. Slower or faster torquing
action will detract from accuracy.


***
Maybe measure at six locations.   You did later state anywhere on the red handle, but with the 3 closer to the pivot point, I expect you will measure a big increase.  While you asked about where the pivot point was for your wrench, I think once you place your finger in the far left location and apply force, you will have answered that one for yourself.

Sounds like you have your work cut out for you.  Looking forward to your video (which if it's like your others will certainly be worth watching.) 

For what it's worth, my 1-minute clip shows about 10% of the experiments I actually performed, and for the record, yes, you can apply much more than the rated torque if you intentionally hold the wrench near the pivot point. 

News flash #1: tools can be misused.  Ric Romero has more on this late-breaking story at 11.  News flash #2: you have to go out of your way to misuse this particular torque wrench in a way that results in significant overtorque.

The digital torque wrench is actually pretty decent for the price, and it does have a peak-reading feature, but I found that the impulse imparted during breakover made the measurement less repeatable rather than more.  The peak-hold feature appears worthwhile at higher torques, but this was very close to the lower end of the wrench's range.

[joeqsmith]

A sane person follows the manufactures procedures. 

I was expecting  you to follow their instructions below, but you would need to ditch the cheap torque meter for a peak reading meter.   Of course, the absolute values are meaningless but at least you could get some relative data.    Then, don't cover up the handle with your hand as you show.  Maybe just use a finger and work your way up the handle in one inch increments. 

• To improve performance of a wrench that hasn’t been used recently, actu-
ate the wrench by clicking the wrench head back and forth several times
before use. This will spread the lubricant through the internal mechanism.
• Click type tools require smooth consistent application of force. Each torqu-
ing action should be completed within 2 seconds. Slower or faster torquing
action will detract from accuracy.


***
Maybe measure at six locations.   You did later state anywhere on the red handle, but with the 3 closer to the pivot point, I expect you will measure a big increase.  While you asked about where the pivot point was for your wrench, I think once you place your finger in the far left location and apply force, you will have answered that one for yourself.

Sounds like you have your work cut out for you.  Looking forward to your video (which if it's like your others will certainly be worth watching.) 

For what it's worth, my 1-minute clip shows about 10% of the experiments I actually performed, and for the record, yes, you can apply much more than the rated torque if you intentionally hold the wrench near the pivot point. 

News flash #1: tools can be misused.  Ric Romero has more on this late-breaking story at 11.  News flash #2: you have to go out of your way to misuse this particular torque wrench in a way that results in significant overtorque.

The digital torque wrench is actually pretty decent for the price, and it does have a peak-reading feature, but I found that the impulse imparted during breakover made the measurement less repeatable rather than more.  The peak-hold feature appears worthwhile at higher torques, but this was very close to the lower end of the wrench's range.

I'll leave it to you to prove your own statements with math.

[KE5FX]

Math without the right model is a waste of time.  Models that involve tying a string to the wrench and applying a normal force to a single point in the middle of the handle are not useful for describing how the tool will actually work, because they don't reflect how the tool is actually used. 

Likewise, models that involve grasping the moment arm near the pivot point are only useful for demonstrating what happens during intentional, negligent misuse.

The problem is, the .PDF warns that holding the wrench anywhere other than the very end of the handle constitutes misuse.  That's simply wrong, and I'm satisfied that I've shown that.  I'll leave any remaining work to those who continue to assert otherwise.

[joeqsmith]

Math without the right model is a waste of time.  Models that involve tying a string to the wrench and applying a normal force to a single point in the middle of the handle are not useful for describing how the tool will actually work, because they don't reflect how the tool is actually used. 

Likewise, models that involve grasping the moment arm near the pivot point are only useful for demonstrating what happens during intentional, negligent misuse.

The problem is, the .PDF warns that holding the wrench anywhere other than the very end of the handle constitutes misuse.  That's simply wrong, and I'm satisfied that I've shown that.  I'll leave any remaining work to those who continue to assert otherwise.

So you want others to show you the math but feel that is has no value?   While I am sure many a free energy Tesla believers also are satisfied with what they show.   They too always ask the public to run the test. 

Seems you are trying to constrain how users hold the wrench now rather than your original comments that it doesn't matter.   Progress....

[KE5FX]

Yep, I was out of line to suggest that it didn't matter at all.  It clearly does, in the sense that grasping the wrench well away from the end of the handle can apply significantly more torque at breakover.

Someone reading what I wrote would come away with the impression that you can't misuse a torque wrench.  That wouldn't serve students any better than the overly-conservative advice in the .PDF does.  Like I said, I wouldn't defend that hill any further.

[joeqsmith]

While most hams tell me that torque wrenches are pointless, here is a ham with several.     

[KE5FX]

You'd never catch me saying they're pointless, wearing either my ham hat or my professional hat. 

The .PDF triggers me because I have to write documents like that.  If I tell people to do something obviously goofy, not only will they not do it, they will start to wonder what else they can safely ignore.

[G0HZU]

To help try and resolve this issue, I waited until I was back at work today.   ....

Does your company have a set of gages to repeat the OPs measurements?   Or, I wonder if you or your company has seen a similar trend? 

***
I'm curious if your company produces any products that use RF connectors during testing, and it so do they torque them?

In terms of pin depth gauges for various RF connectors and stuff like that I doubt the company has these but I might be wrong.

I'm curious if your company produces any products that use RF connectors during testing, and it so do they torque them?

I work for a very large defence company that makes lots of RF based equipment so lots of RF connectors are involved during manufacture and test. Obviously, torque wrenches are used and this is why there are various torque tester stations to check the torque wrenches

RF cables generally get made by Suhner (and similar companies) to the company drawings. This is why I doubt there will be any pin depth gauges. If there are any, they will probably be securely locked away for special occasions. I'm not aware of any issues when Suhner make cables and these cables are typically used at high RF power levels up at many GHz.

[joeqsmith]

You'd never catch me saying they're pointless, wearing either my ham hat or my professional hat. 

The .PDF triggers me because I have to write documents like that.  If I tell people to do something obviously goofy, not only will they not do it, they will start to wonder what else they can safely ignore.

In general, people will not take the time to read or do their own research.  I don't believe I'm biased from interacting with the hams and hobbyists.  A good example is TV ads where dad assembles some furniture, kids toy...  Parts are left over and they fall apart...  Maybe entertaining on some level but I suspect it's closer to reality.   

On the flip side, how many times have you had to contact the creator of a document  to determine what they meant.   Datasheets,  standards.....   In the age of so many companies trading hands and marketing getting involved with changing datasheets, it hasn't gotten any easier.

Recently reached out to viewer's to proof a document I am working on for some software I wrote.  I was surprised by the amount of good feedback they provided.   So there are a few of us out there who still read.   

[joeqsmith]

To help try and resolve this issue, I waited until I was back at work today.   ....

Does your company have a set of gages to repeat the OPs measurements?   Or, I wonder if you or your company has seen a similar trend? 

***
I'm curious if your company produces any products that use RF connectors during testing, and it so do they torque them?

In terms of pin depth gauges for various RF connectors and stuff like that I doubt the company has these but I might be wrong.

I'm curious if your company produces any products that use RF connectors during testing, and it so do they torque them?

I work for a very large defence company that makes lots of RF based equipment so lots of RF connectors are involved during manufacture and test. Obviously, torque wrenches are used and this is why there are various torque tester stations to check the torque wrenches

RF cables generally get made by Suhner (and similar companies) to the company drawings. This is why I doubt there will be any pin depth gauges. If there are any, they will probably be securely locked away for special occasions. I'm not aware of any issues when Suhner make cables and these cables are typically used at high RF power levels up at many GHz.

Thanks,  this is some good insight.  Can they not achieve consistent results by hand tightening?  If that is not the problem, care to elaborate on the reasons for their use?     

It would be interesting to check if they did have gages for male SMA connectors.   Maybe then you could check a few cables and post your results.   

I mentioned I have an assortment of manufactured cables.  Some of these were made by Digi-Key.  I have some really cheap ones from Amazon.   I thought about measuring what I have on-hand and providing that data.   I wrote CentricRF and provided them a link to this thread.  I offered to test some of their cables independently.  If they take me up on it, I'll put some sort of test together. 

[G0HZU]

I think a lot depends on the intended application. For cables using N connections that have to withstand vehicle use it's possible to use N connectors that can support a torque tool.
See below for a typical example. This is obviously going to be better than hand tightening.

For general bench use, it's generally fine to hand tighten N connectors.

I have seen issues with SMA cables that have been hastily assembled by technicians (using Suco 141 cable) where the male pin ends up at the wrong depth. I've seen it where is it obviously wrong even with the naked eye. No need for any gauges!

However, the cable issue I see most often is when thicker RF cables aren't crimped well at the connectors. This can cause leakage issues and suckouts up at many GHz. It's easy to spot this if the cable is measured on a VNA and the cable is wiggled near its ends. This generally happens if cables are ordered (to a custom length) from alternative suppliers if someone needs the cable(s) quickly. It's always very disappointing to see this when it happens.

[tautech]

I think a lot depends on the intended application.
.........
For general bench use, it's generally fine to hand tighten N connectors.

Advanced VNA afficiardos will disagree.

[G0HZU]

I think a lot depends on the intended application.
.........
For general bench use, it's generally fine to hand tighten N connectors.

Advanced VNA afficiardos will disagree.

I'm really referring to operation (evaluation)  of the same (vehicle based) equipment on a bench. It's generally fine to attach N cables or N attenuators to it and just hand tighten them. Often the cable or attenuator won't support a torque tool anyway.

[tautech]

I think a lot depends on the intended application.
.........
For general bench use, it's generally fine to hand tighten N connectors.

Advanced VNA afficiardos will disagree.

I'm really referring to operation (evaluation)  of the same (vehicle based) equipment on a bench. It's generally fine to attach N cables or N attenuators to it and just hand tighten them. Often the cable or attenuator won't support a torque tool anyway.

Real results have suggested otherwise and now I alway tighten N type.....especially for a VNA.
SMA are a quite different beast but both benefit from torquing to provide repeatable results.

[G0HZU]

I think a lot depends on the intended application.
.........
For general bench use, it's generally fine to hand tighten N connectors.

Advanced VNA afficiardos will disagree.

I'm really referring to operation (evaluation)  of the same (vehicle based) equipment on a bench. It's generally fine to attach N cables or N attenuators to it and just hand tighten them. Often the cable or attenuator won't support a torque tool anyway.

Real results have suggested otherwise and now I alway tighten N type.....especially for a VNA.
SMA are a quite different beast but both benefit from torquing to provide repeatable results.

I wasn't referring to VNA use I was referring to general benchwork using N connectors. This could mean connecting a general test cable to an attenuator or a spectrum analyser. The connectors often don't have flats on them for a torque wrench.

However, I have used N type VNA cal kits without a torque wrench many times. A torque wrench is obviously better but often it isn't necessary. This is based on decades of experience working in RF labs. Not all measurements have to follow metrology guidelines just like not everyone has to measure stuff using metrology grade equipment whilst following metrology grade procedures.

Often, I'll re-use stored cal setups months later. I do this to save time on occasions where I don't need great accuracy or low uncertainty.

Also, for the more critical applications, the dominant uncertainty/errors will often be due to cable wear issues and cable flexing (during the cal process) and issues with the test fixture and the limitations of the VNA hardware itself.

[joeqsmith]

I think a lot depends on the intended application. For cables using N connections that have to withstand vehicle use it's possible to use N connectors that can support a torque tool.
See below for a typical example. This is obviously going to be better than hand tightening.

For general bench use, it's generally fine to hand tighten N connectors.
...

I would have guessed that your production test fixtures would be a similar environment to general bench use.  Which gets back to why does your company torque connections for production?  Consider the costs not just the operation, but tracking, calibration... 


Attached is an interesting memo on the use of SMAs.  A few quotes related to connector torque.   

However, at both organizations, SMA connectors are routinely torqued to the recommended torque, "plus a bit", the extra "bit", which is deemed important to long term reliability, being at the discretion of the assembler. This is not sufficiently well defined for use as an ALMA standard procedure.

[/i]

Galen Watts [14] writes: "...I use a procedure where I bring the SMA to full torque (wrench click), wait a couple seconds, full torque again, wait a couple seconds, full torque a third time, all while counter torquing with a plain wrench when possible or pressing lightly on rigid/semi rigid coaxial cable counter to the torquing direction when applicable. Following this procedure I have not yet seen loose SMA connectors in cryogenic applications after multiple temperature cycles..." He notes that "...the  SMA  shell  will  frequently  turn  a  little  farther  on  the  second  and  often  the  third application of the same torque."

Suggestions for ALMA
(i) The connector should be tightened to a torque of 8 in-lb (88 N-cm) unless otherwise specified by the manufacturer.
(ii) The torque wrench should be applied three times in succession.
(iii) A second wrench should be used where appropriate to prevent rotation of the body of the connector. This is facilitated by the use of male SMA connectors with a hexagonal section behind the nut and female SMA connectors with a hexagonal section behind the thread [8].
(iv) Striping or gluing SMA connectors should not be done unless it becomes clear during early ALMA operation that it is necessary.

[G0HZU]

I'm not sure where this is all leading... at work, there is a difference between 'general bench work' and production ATE procedures. The ATE stuff is very strict for obvious reasons.

General bench work might involve the manual checking of a unit that has failed a phase noise or a spurious test or maybe it has some other issue. If it can't be sorted by the test engineers I would typically get called across to look at it if it was something I was involved in the design of.

Other bench work might involve R&D work. It generally isn't necessary to use torque tools for stuff like this especially when rapidly cable swapping between analyser types or a scope or something else.

I really just joined this thread to try and prove that the Keysight torque tools are meant to be held a certain way or the accuracy (and repeatability) of the torque will begin to degrade. It should be obvious with this type of tool that uncertainty will creep in if the pressure points on the tool are poorly defined across various fingers and a thumb. I couldn't back any of this up using real tests with the relevant hardware until I was at work on Monday.

The repeatability is really impressive if used the way suggested by Keysight as this defines how and where the force is applied by the user. Any attempt to use a different type of grip will result in impaired repeatability and the torque can be greater or lower than the torque the tool is calibrated for.

However, it generally doesn't make a great deal of difference unless the tool is gripped in an unnatural way or if it is used nearer the pivot point. But the difference is real and easy to demonstrate. Keysight do describe this stuff in the various cal kit manuals. It's up to the individual if they want to strive for the most accurate torque each time they use this tool. I don't have a Keysight torque tool here at home, just the little Suhner torque tool.

[joeqsmith]

I'm not sure where this is all leading... at work, there is a difference between 'general bench work' and production ATE procedures. The ATE stuff is very strict for obvious reasons.
....

I have read numerous times how finger tight is repeatable, good enough, torque wrenches are pointless......  Assuming any of that is true,  I am asking specifics of why you can't get away with finger tightening your connections in production.  Maybe you expand on what these obvious reasons are.     

Looking at my old HP VNA, the N connectors do not have a flats.  Even the APC-7 connectors are finger tight only.  That setup's upper limit was only 2.6GHz, and really, what's the accuracy of a grease pen on the screen....   

I don't believe the lack of requiring a torque wrench was just because of the low frequency.   I have an old Adam Russell N style cable rated for 18GHz.  It is marked at both ends "DO NOT WRENCH CONNECTOR". 

[Someone]

It is marked at both ends "DO NOT WRENCH CONNECTOR".

In some industries/settings tightening a fastener is done until it yields, so I can fully appreciate the need for such a warning.

[joeqsmith]

It is marked at both ends "DO NOT WRENCH CONNECTOR".

In some industries/settings tightening a fastener is done until it yields, so I can fully appreciate the need for such a warning.

[mark432]

Wow there's a lot of gibberish in this thread.

1) You cannot reach the recommended torque for an SMA with your fingers.  Use a wrench.  If you insist on being fast and imprecise, spend $5 on a hasco SMA finger wrench.
https://www.hasco-inc.com/tools/sma-3-5mm-2-92mm-2-4mm-1-85mm-connector-finger-thumb-wrench-blue/
That will at least increase the diameter to a size where you can apply the required torque.

2) Type N connectors were designed back when dinosaurs roamed the earth.  They were designed to be hand tightened.  It is at least possible to hit the right torque without a tool.  Since those days, the precision grade parts available today benefit from repeatable torque.  Please don't be one of the clowns that grabs a pair of cannon pliers and tries to put 60 ftlbs on it.  You'll find different hex sizes and torque specs for type N. 

3) MIL-STD-348 is just an interface spec.  If you expect it to tell you everything about the SMA connector you're being lazy.  You need to go hunt through 39012 and relevant "slash" sheets and quite likely commercial specs as well depending on what you're doing.

4) Connector gauges are generally comparators against a reference standard.  Check your reference.  Is it good?  This is easy for SMA but harder for N.  Either way, I didn't notice any reference to zeroing the gauges.

5) If your torque wrench appreciably changes its delived torque based on where your fingers are on the handle, it is a POS and belongs in the trash.  Typical RF connector torque wrenches do not have this property.  Don't use a $10 beam torque wrench with a crowsfoot or whatever nonsense.  It looks like you can buy a knockoff for $35.

6) I've definitely had batches of bad cables from pros.  It happens. There's still a lot of hand labor in RF cable assembly.

7) I don't think I'd ever buy used RF cables.  Cables get abused.  Pulled.  Twisted.  Kinked.  Run over by office chairs.  Thermal cycled.  Shaken.  Etc.  A multi thousand dollar VNA cable can look great visually, and still be toast electrically.  I think I'd rather buy a rental car.

[Smoky]

That little blue wrench is perfect

https://www.hasco-inc.com/tools/sma-3-5mm-2-92mm-2-4mm-1-85mm-connector-finger-thumb-wrench-blue/

[joeqsmith]

Wow there's a lot of gibberish in this thread.

And thank you for taking the time to add even more gibber jabber.

1) You cannot reach the recommended torque for an SMA with your fingers.  Use a wrench.  If you insist on being fast and imprecise, spend $5 on a hasco SMA finger wrench.
https://www.hasco-inc.com/tools/sma-3-5mm-2-92mm-2-4mm-1-85mm-connector-finger-thumb-wrench-blue/
That will at least increase the diameter to a size where you can apply the required torque.

I have some open end wrenches I could use if the goal was to over torque them.  I assume you are suggesting that is not possible with the tool you are recommending. 

4) Connector gauges are generally comparators against a reference standard.  Check your reference.  Is it good?  This is easy for SMA but harder for N.  Either way, I didn't notice any reference to zeroing the gauges.

I can easily remedy that.  See attached image.  Feel better now?

Now, how good is that standard?

5) If your torque wrench appreciably changes its delived torque based on where your fingers are on the handle, it is a POS and belongs in the trash.  Typical RF connector torque wrenches do not have this property. 

I really don't know what "appreciable" changes are or what a "typical" wrench would be.   No matter, finger placement has been covered but rather then posting gibberish,  feel free to prove me otherwise.  Plot the six or so data points I previously asked for.   

https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/msg5752031/#msg5752031

[mark432]

Wow there's a lot of gibberish in this thread.

And thank you for taking the time to add even more gibber jabber.

Gee.  I can't imagine how your interactions with manufacturers didn't go the way you wanted them to.
 

1) You cannot reach the recommended torque for an SMA with your fingers.  Use a wrench.  If you insist on being fast and imprecise, spend $5 on a hasco SMA finger wrench.
https://www.hasco-inc.com/tools/sma-3-5mm-2-92mm-2-4mm-1-85mm-connector-finger-thumb-wrench-blue/
That will at least increase the diameter to a size where you can apply the required torque.

I have some open end wrenches I could use if the goal was to over torque them.  I assume you are suggesting that is not possible with the tool you are recommending. 

You do know what happens when you assume right?
That tool means that you will at least apply enough torque to mate the reference planes and compress any gasket.  The basic, bare minimum requirement. 
It will remind you that these are just SMA connectors as it starts to slip, but they's nothing to stop you from just acting like a fool and tightening your grip.

If you have to make a quick check on 100 units, it's just the ticket.  An open end wrench will be slower and more prone to over torque.

4) Connector gauges are generally comparators against a reference standard.  Check your reference.  Is it good?  This is easy for SMA but harder for N.  Either way, I didn't notice any reference to zeroing the gauges.

I can easily remedy that.  See attached image.  Feel better now?

Now, how good is that standard?

Quit being lazy and tell us.  What number are you zeroing to? 

I said "check you reference" not " blindly trust it."

5) If your torque wrench appreciably changes its delived torque based on where your fingers are on the handle, it is a POS and belongs in the trash.  Typical RF connector torque wrenches do not have this property. 

I really don't know what "appreciable" changes are or what a "typical" wrench would be.   No matter, finger placement has been covered but rather then posting gibberish,  feel free to prove me otherwise.  Plot the six or so data points I previously asked for.   

https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/msg5752031/#msg5752031

If you can't define an appreciable change in torque perhaps you should leave the discussion alone.  Go look at the torque spec.  It's a range.  All torque specs produced by serious people are.

Commonly 8-10 in lbs
https://www.centricrf.com/torque-specifications/

Thus a change of 0.2 in lbs would be insignificant whereas a change of 2 in lbs would.

This is obvious, common sense stuff.
If you insist on not using common sense you could go buy yourself a copy of a torque wrench standard like ISO 6789.


As for "typical" you do at least seem to speak English.  You should know what "typical" means.  Go do some searching as if you were going to buy an SMA torque wrench.  What are the most common types?  That's typical.  Typical is a "clicker" style.

This is not hard stuff.  Maybe twisting a male connector onto a female connector is just not for you.  Maybe you should just use SMB connectors.

[nctnico]

5) If your torque wrench appreciably changes its delived torque based on where your fingers are on the handle, it is a POS and belongs in the trash.

It has been proven mathematically that torque wrenches based on a click mechanism are sensitive to position of where the force is applied due to the difference in arm length between the rotation point of the jaw and the pivot point of the click mechanism. I'll admit it is something that takes some time & thought to wrap your head around but this is basic physics.

[KE5FX]

I really don't know what "appreciable" changes are or what a "typical" wrench would be.   

That seems to be the heart of the problem.  What is "appreciable" or "significant"? 

When I write assembly instructions for EMS personnel, job #1 is to get them to use a torque wrench at all.  Training the assemblers in a 40,000-square foot ISO-certified facility in the Bay Area, it was surreal to discover that none of them had ever seen an SMA torque wrench before.  Although there was no shortage of RF hardware being shipped out of that factory, my product was either the only one that specified connector torques, or the only one whose instructions explicitly called for a torque wrench to be used.

Beyond that, I'm happy if the torque applied is within, say, -25% to +50% of the rated amount.  Decent-quality SMA connectors are going to work just fine in the 6-12 in-lb range.  Just as the equipment breakage described in the university lab manual .PDF was not caused by students holding a torque wrench incorrectly, the quality issues I saw weren't caused by tolerance violations.  They were caused by connectors being left untorqued entirely. 

Ultimately the best solution was a redesign that eliminated 80% of the connectors and left the others more easily accessible.  Lots of lessons were learned on that project, some by the assemblers but mostly by me.

The NRAO guidelines posted above are pretty interesting in that regard.  They are telling people to torque each connector 3 times, and I'm kicking myself for not thinking of that.  Instead of my assemblers being unsure if they have torqued a given connector at all, the NRAO assemblers are going to fret about whether they've applied the wrench 3 times or only twice.

No matter, finger placement has been covered but rather then posting gibberish,  feel free to prove me otherwise.  Plot the six or so data points I previously asked for.

Nobody is going to do all this work for you, Joe, and if they do, it probably won't prove what you're hoping it will.  (Which is what, exactly?)  A half-assed video is about all you can expect for free.

[joeqsmith]

Wow there's a lot of gibberish in this thread.

And thank you for taking the time to add even more gibber jabber.

Gee.  I can't imagine how your interactions with manufacturers didn't go the way you wanted them to.
 

Nice, more gibber added to the pile, compliments of the person complaining about it.

Wanted?  You do realize that there is NOTHING for me to gain by running such a test.  My offering to run an independent check wasn't /isn't something I wanted to do but certainly would.   

1) You cannot reach the recommended torque for an SMA with your fingers.  Use a wrench.  If you insist on being fast and imprecise, spend $5 on a hasco SMA finger wrench.
https://www.hasco-inc.com/tools/sma-3-5mm-2-92mm-2-4mm-1-85mm-connector-finger-thumb-wrench-blue/
That will at least increase the diameter to a size where you can apply the required torque.

I have some open end wrenches I could use if the goal was to over torque them.  I assume you are suggesting that is not possible with the tool you are recommending. 

You do know what happens when you assume right?

The sarcasm slipped past you. 

That tool means that you will at least apply enough torque to mate the reference planes and compress any gasket.  The basic, bare minimum requirement. 
It will remind you that these are just SMA connectors as it starts to slip, but they's nothing to stop you from just acting like a fool and tightening your grip.

That was my point.

4) Connector gauges are generally comparators against a reference standard.  Check your reference.  Is it good?  This is easy for SMA but harder for N.  Either way, I didn't notice any reference to zeroing the gauges.

I can easily remedy that.  See attached image.  Feel better now?

Now, how good is that standard?

Quit being lazy and tell us.  What number are you zeroing to? 

To the master gage.

[joeqsmith]

No matter, finger placement has been covered but rather then posting gibberish,  feel free to prove me otherwise.  Plot the six or so data points I previously asked for.

Nobody is going to do all this work for you, Joe, and if they do, it probably won't prove what you're hoping it will.  (Which is what, exactly?)  A half-assed video is about all you can expect for free.

Referring to:

If your torque wrench appreciably changes its delived torque based on where your fingers are on the handle, it is a POS and belongs in the trash.

I'm really not asking or expecting anyone to as it should be obvious that once you choke up beyond the pivot, you have bypassed the mechanism.  Your acknowledgement     

Yep, I was out of line to suggest that it didn't matter at all.  It clearly does, in the sense that grasping the wrench well away from the end of the handle can apply significantly more torque at breakover.

was all I was looking for.   

[joeqsmith]

The NRAO guidelines posted above are pretty interesting in that regard.  They are telling people to torque each connector 3 times, and I'm kicking myself for not thinking of that.  Instead of my assemblers being unsure if they have torqued a given connector at all, the NRAO assemblers are going to fret about whether they've applied the wrench 3 times or only twice.

I was surprised when I read that comment by Galen Watts.  I've never paid any attention to if the connector would move on a second  or third application.  They talk about temperature causing the connectors to loosen. 

I play a bit with motorcycles and assemble my own motors for them.   To torque the head, you work the pattern at a low level of torque, then the final level.   Then repeat at the final level.   Then you let the motor run and repeat it again at the final level.   Much higher torque levels, and wider temperatures.  Plus compressing copper gaskets.   

It's a different game than a little SMA but I guess they can have similar problems.   

***
Just to add,  most of the engine parts are aluminum.  Tempco is really poor.   I am surprised NRAO wouldn't use stainless to get that temperature stability.   Maybe they are. 

[KE5FX]

I play a bit with motorcycles and assemble my own motors for them.   To torque the head, you work the pattern at a low level of torque, then the final level.   Then repeat at the final level.   Then you let the motor run and repeat it again at the final level.   Much higher torque levels, and wider temperatures.  Plus compressing copper gaskets.   

It's a different game than a little SMA but I guess they can have similar problems.   

Yeah, ultimately we're arguing about how best to do a robot's job.  High-precision repeatability requires specifying all of the conditions including how to account for operating temperature variations (hence the NRAO notes.)

I will say that one problem with the six-point test is that there is no way to apply all of the force to one point or even two adjacent points without holding the wrench in a VERY unnatural way.  Such as by hooking one finger around it and pulling at 90 degrees. 

Doing that at the very end of the handle results in the correct torque.  Doing it below the halfway point results in substantial overtorque, meaning more than my personal abs-max limit of 12 in-lb.  But again, it proves nothing other than that the wrench can be misused if you try hard enough.

The other point you raised, regarding applying smooth force over about 2 seconds, is more important than I would have guessed.  The longer I spent trying to get a clear reading on the digital torque wrench, the less reproducible the result... or rather, the less confidence I had in it.

[joeqsmith]

...

I was expecting you to make a fully automatic test fixture with a simulated finger.   Your idea of using a robot would be fine.   EEVBLOG recently lost the worlds leading expert in robotics.  I bet he could have pulled it off with some fishing line, old socks along with his AI. 

***

...proves nothing other than that the wrench can be misused if you try hard enough...

Suggesting that it doesn't matter (hand finger placement) at all, invites such misuse.  We don't put warning labels on poison telling people not to drink it because we are intelligent.      

I have had friends who have worked in the medical and nuclear industries.  I am always amazed about how detailed their procedures are.   There's no room for cowboys.

***
Cowboy as a verb. 

a person who is reckless or careless, especially when driving an automobile.

An engineer running in a vacuum, no peer review, doing their own thing.  A prodigy, perhaps Mr Bigs kid.... 

Mr Big?  The man, boss, owner of small company, who ever you work for.... 

[KE5FX]

I'm sure he'll be back.  They always come back.

[mark432]

5) If your torque wrench appreciably changes its delived torque based on where your fingers are on the handle, it is a POS and belongs in the trash.

It has been proven mathematically that torque wrenches based on a click mechanism are sensitive to position of where the force is applied due to the difference in arm length between the rotation point of the jaw and the pivot point of the click mechanism. I'll admit it is something that takes some time & thought to wrap your head around but this is basic physics.

Here's a link to what I believe you are referring to


 I haven't checked his work but it seems right. 
I'll give you credit there.   

If you apply force in a different place than expected you can change the result. 

It would certainly be possible to design a clicker wrench that is super sensitive to hand position.

Given all this:
You need to keep in mind the expected and required level of precision and accuracy for various tasks.
Torquing an RF connector is more of a within 20% with decent repeatability is fine type of activity.  You don't need 1%.

Still, it's a bit surprising manufacturers don't just have the 5/16 open end exit the handle at a 90 degree angle to eliminate this effect entirely, as is standard practice with use of torque adapters.

But I suppose it still comes down to being " good enough"

[mark432]

Wow there's a lot of gibberish in this thread.

And thank you for taking the time to add even more gibber jabber.

Gee.  I can't imagine how your interactions with manufacturers didn't go the way you wanted them to.
 

Nice, more gibber added to the pile, compliments of the person complaining about it.

Wanted?  You do realize that there is NOTHING for me to gain by running such a test.  My offering to run an independent check wasn't /isn't something I wanted to do but certainly would.   

Obviously you want something.  Look at the title of the thread.

Boohoo!   Don't buy from this company because I couldn't bully them into doing what I want!

What could you gain?   Oh I don't know. Maybe you were looking for free product.

To the master gage.

Which is what?  Quit being lazy.  You did check it right?  Is it calibrated.  Do you have something else to check it with?


You're stating measurements down in the fractions of mils remember. 

[G0HZU]

My advice to anyone unfamiliar with this stuff is to read the manual for the VNA cal kits that have the Keysight 8710-1765 torque wrench in it
The manual explains what can go wrong if you don't use the torque tool correctly. It tells you that you can't get consistent readings if you hold it differently.

If you experiment with different grip types you can also achieve under-torque even though it feels (to the operator) like the tool is being held nearer to the break point.

The golf club grip should result in a lower break point because the handle can act as a lever that pivots around the thumb. I could easily see a -20% error with this grip type.
Other grip types can introduce more subtle errors but the repeatability will suffer because the forces applied by the fingers and thumb and maybe even the palm of the hand will be distributed differently each time the tool is used.

Hold it and use it correctly and the accuracy and repeatability is much improved.

[joeqsmith]

Wanted?  You do realize that there is NOTHING for me to gain by running such a test.  My offering to run an independent check wasn't /isn't something I wanted to do but certainly would.   

Obviously you want something.  Look at the title of the thread.

Boohoo!   Don't buy from this company because I couldn't bully them into doing what I want!

What could you gain?   Oh I don't know. Maybe you were looking for free product.

ROFLMAO!   I'm not so hard up that I can't afford cables.  I actually work for a living.  Also, my current selection of RF cables are fine (or I would buy what I needed).   Your idea of free products is false.  It's rare I will accept products, but there have been a few exceptions.   When I consider my own investment in these so called free products, I am still in the negative.     

To the master gage.

Which is what?  Quit being lazy.  You did check it right?  Is it calibrated.  Do you have something else to check it with?

You're stating measurements down in the fractions of mils remember.

Similar to suggesting I would have a way to calibrate any other equipment I have.   You would have to be very naive to suggest anyone would have a NIST traceable calibration equipment.   Like the kids suggesting I check my meter meters with one of those cheap "standards", or worse, try to align to them... 

I have no way to check a master gage outside of sending them in for calibration.  Because the masters are not used as punch to drive nails,  I am confident in their original factory specs.   Maybe you do not understand that the dial indicator gages are not a master gage.   In that photo, the master can be seen at the business end of the dial indicator (see attached).

***
A quick search of NIST for  gauge, block, calibration &  certification,  revealed the following paper detailing what is involved.   Welcome to the world of metrology... 

https://www.nist.gov/system/files/documents/calibrations/mono180.pdf

[joeqsmith]

I used both the Maury A027 SMA push-on gages and the (much more accurate) 3.5mm thread-on gages from an HP 85052B calibration kit. Both of my gages are designed to measure pin protrusion/recession.  I do not have the Maury kit to measure dielectric protrusion/recession and (of course) this would not be applicable for 3.5mm connectors.

I've used my 3.5mm gauges to measure some SMA adapters/cables purchased from eBay and the results where concerning.  Quite a few male center pins extended too far out beyond specification.  This can clearly damage a quality 3.5mm connector and maybe even another mating SMA connector.  Until you have an indicator/gauge you're kinda flying blind.

https://www.eevblog.com/forum/rf-microwave/testing-rf-connectors-and-cables/msg2733738/#msg2733738

[joeqsmith]

Sadly, I never did hear back from CentricRF.  Maybe they are closed for the holidays.   I thought for fun I could look at a few lower grade cables I have.   This set includes one from Digi-key, LiteVNA, V2Plus4 VNA, a very low cost one from Amazon, and the ones I used for my 10GHz experiments with the EPR spectrometer.

[joeqsmith]

Remember how I stated that the pins vary a lot.  SMAs are not precision connectors.  So before I do anything else, I'll take some photos of what we are dealing with.  Maybe we can't even measure these accurately.   

This first two photos are the cables I use for my high frequency experiments.  Notice the more common thin outer conductor and the  stepped 
(conventional) male pin.   Notice the OD of the step and how flat the surface appears.  Also note that the dielectric is not interfering with the pin's step in anyway. 

You can also see how the dielectric is recessed from the reference plane and the step appear basically level with the dielectric.  I have no doubt we could accurately measure the reference plane to the step, dielectric and pins tip.

[joeqsmith]

I recently picked up some very low cost cables off Amazon from China.  These are very interesting as these don't use a stepped pin or a thru.  I would place it into the angled category. 

Notice how the pin is machined in a stair step pattern.  While the dielectric doesn't interfere with the pin,  the gage is designed to measure a flat surface.  Who knows which stair step it will catch on and measure to. 

So while I could easily measure the reference plane to the dielectric and pin height, there is no way I could reliably measure where the step is.

[joeqsmith]

Looking at a custom cable from Digi-key.  Note the wider outside conductor's mating surface.  More important to this discussion, there is no step.   Again, I could measure the dielectric and pin positions but we can't measure a step that doesn't exist.

[joeqsmith]

The LiteVNA is rated up to 6GHz and is supplied with cables.  I think we paid about $120 for the first Lites.  These last ones were $150 or so. The cables have not appeared to have changed over the three hardware revisions I have looked at. 

Notice how it appears to use a stepped type pin, but the outside diameter of the step is very small.  The gage's pin also has a thickness.  While the steps OD may be large enough for the gage to sit on it, the dielectric may interfere with the measurement. 

[joeqsmith]

I like the rubberish feel to the cables supplied with the V2Plus4 VNA.  They are very flexible.   They appear to made of brass rather than stainless like the LiteVNA's cables.   

Notice again how the pin appears to have a step for how the dielectric is again interfering with the surface of the step.   

If I were to blindly gage this connector without knowing what the pin looked like,  I may be measuring the raised part of the dielectric.   

Maybe you see what I am driving at.  Of all of these cables, really the only one I would have any confidence in measuring the pin step's position is the first one. 

[joeqsmith]

For a comparison, let's look at an SMA used on a cable produced by Gore.   I'm sure I could easily measure this connector.   

[shabaz]

It feels too much to expect SMA cables to be very precise as you say. I'm no expert in this though, and don't have anything other than some instinct to back that up, from visual inspection of the pieces and how they are put together.

Slightly off-topic, but I got curious to see how center-contact depth is set on SMB connectors.

The only few products I've worked on that used similarly-sized connectors didn't have SMA but rather used right-angle SMB connectors internally, and so, for a while, I thought I'd standardize on SMB for my home lab too, but SMA simply had more general traction, so I aborted that idea pretty quickly.

I don't think I've ever assembled a straight SMB connector (I bought ready-made SMB cables for my home lab at that time, and maybe assembled a few right-angle ones where the center pin is pre-fitted). Anyway I took a look at the assembly instructions for some straight Amphenol SMB connectors, and it's so much more simplified than straight SMA assembly. No need for dielectric insertion tools, nor pin depth setting tools. Still not a precision solution, but for that sort of sized board-to-board connections inside a product, it is attractive.

[joeqsmith]

It feels too much to expect SMA cables to be very precise as you say. I'm no expert in this though, and don't have anything other than some instinct to back that up, from visual inspection of the pieces and how they are put together.

I did provide that Maury paper that you could read where they discuss the SMA and the 3.5mm precision connectors.  I'm sure Google would find a lots of hits as well. 

I took a photo for you of the cables I put together for my HP8754A VNA. 
https://www.eevblog.com/forum/testgear/dont-buy-sma-cable-assemblies-from-centricrf/msg5746121/#msg5746121

Attached showing a closeup of the male pin.  Again, notice the step's wide OD and no interference with the dielectric.  An easy one to measure.   

[Smoky]

To add to the collection, here's a picture of the SMA connector on Amphenols ATC Phase Stable series of cables:



Part number 095-902-466-001

Looking closer, notice how loose the center contact is within the dielectric:



Amphenol claims that these SMA connectors are rated for 5000+ mating cycles.

[joeqsmith]

To add to the collection, here's a picture of the SMA connector on Amphenols ATC Phase Stable series of cables:

Part number 095-902-466-001

Looking closer, notice how loose the center contact is within the dielectric:

Amphenol claims that these SMA connectors are rated for 5000+ mating cycles.

It looks like the step protrudes beyond the dielectric a fair amount, and the dielectric is recessed from the reference plane.   Do you have a  way to measure it?

I bought some used cables for my HP3589A that appear to be custom made using Suhner connectors.  These get a fair amount of use and it looks like I purchased them in 2011.  What is interesting about the SMA is that double step feature.    I wonder again if the gage would touch off on that first step or the second.  Imagine if it measures the lower step and the upper one protrudes beyond the reference.   

I think it is safe to say if you want to measure them, it is not as simple as buying a gage, zeroing it to a standard, cleaning all the parts, press on the gage and bingo... Personally, I always start with a visual inspection.  I'm surprised the big players don't have any training videos that cover the SMA in particular because there are so many variations.   

[joeqsmith]

As that paper discusses, one way to avoid the variations with SMAs is to use a different connector.  Cost goes up and you are presented with new problems, like how to measure your $2 ebay Tees from China without risking your precision connectors. 

https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5665155/#msg5665155

[G0HZU]

For fairly serious VNA use, I think that it's best to simply abandon low and mid range cables and connectors.

For VNA and (e)cal kit and test fixture stuff, I use 18GHz rated Gore and Suhner cables and I use decent 18 GHz rated SMA end launch connectors.
There shouldn't be any need to measure pin depths with any of these because they are high quality items.

I do sometimes use MiniCircuits 18 GHz rated cables like the CBL-3FT-SMSM+ cables. These are quite well made with good shielding but I tend to use these for 4 port measurements below about 1GHz.

For less serious stuff, it's OK to use lower budget (but still decent) cables but I wouldn't recommend connecting them to any precision connectors that also get used with precision cables and connectors because of the risk of damage to the precision connectors. I don't see the measurement of pin depth as a means to reduce the risk as there are various ways that cheaper cables can damage cal kits or other precision connectors.

For casual stuff with a budget VNA, I use a dedicated homebrew cal kit with my nanovnaH for example and I use dedicated cables with it.
To minimise risk, I either use a dedicated connector saver at the end of the lower cost cables or something like a 3dB attenuator from Minicircuits. This isolates the homebrew cal kit and test fixture from the lower cost cables that I use with the nanovnaH.

There's so much to go wrong with the various dimensions and machined surfaces of budget SMA connectors that it won't be cost effective to measure them thoroughly.

[Smoky]

Just looking at the few samples of SMA ends in the pictures reveals differences all across the map. Thick walls, thin walls, stepped and non-stepped contacts, loose dielectrics, tight dielectrics. Now bring in all of the differences that can be found in the receptacles 

[joeqsmith]

Just looking at the few samples of SMA ends in the pictures reveals differences all across the map. Thick walls, thin walls, stepped and non-stepped contacts, loose dielectrics, tight dielectrics. Now bring in all of the differences that can be found in the receptacles 

Which is why I asked early on about if their gage could even measure their particular connectors, why I wanted to see what they looked like and why I posted about mixing the 3.5mm and SMA gages.   

Again, I have no way to know if there was a problem with the OPs measurements or not.  This is also why I had suggested an independent repeating the measurements. 

I could measure three of the eight I show with confidence that we would get something meaningful.  One that has no step.  Four with some sort of step that I doubt I could tell you anything more useful with a gage than what the photo shows.   It doesn't mean those connectors are bad but that I just can't measure them.   


A simple experiment.   I blow out the gages and zero both the pin contact and dielectric gages to the master gage.   Next measure the Digi-key cable which does not have a step.  I would expect both gages to measure from the reference plane to the dielectric.  All measurements in inches.   

Connector 1,  Dielectric 0.0045,  Pin 0.0045
Connector 2,  Dielectric 0.002,  Pin 0.002

While it meets the industry standard, it is a bit high.  The real point of this exorcise is that the two measurements basically match.

Measuring the pin of the cable I use for my X-band EPR experiments,
Connector 1, Pin 0.0025
Connector 2, Pin 0.0005
Very nice.       

Let's try the home made cable for my HP8754A.   
Connector 1, Pin 0.003 

And finally my Gore cable.   
Connector 1, Pin 0.003 
****
I checked the Gore cables dielectric and then using my 3.5mm gage, I remeasured the Pin and get 0.002875 (basically a half division off).  Consider that was a completely different master used to zero this gage, I think it's pretty safe to say we are in the ballpark. 

It seems pointless to attempt to measure the other SMAs as I have zero confidence in what the gages would show.   

[joeqsmith]

I wouldn't suggest that adapters are immune.  To conduct that T-Check experiment, I purchased some very low cost Tees.   I think I paid something like $10 for a 4 pack.  Guessing you could get these even cheaper but I picked them up off Amazon. 

Notice the pins transition to the step has a fairly dramatic radius.   Measuring the pins location:

Connector 1, Pin -0.0005
Connector 2, Pin -0.0015

I had tested this adapter using my Agilent VNA with good results to 9GHz.   There are no detectable signs where it touched off on the female pins.   Measuring one of the sacrificial adapters I used, the female pin is recessed 0.0025 providing enough clearance. 

Two wrongs don't make a right but it certainly can help.