SMA torque wrench

As your probably know SMA connectors must be fitted with the correct torque.

I noticed that, on the Discord @hagbard was mentioning this with respect to the RSP1A SMA connector and his habit of using an SMA torque wrench on all his fittings because it stopped him from overtightening. Cool! Perfect timing for this topic :blush:, I recently was searching for such a wrench after one of my favorite YouTubers was using one. Well… if you know exactly what to search for, then it is doable, but other times it is not as simple! That’s where an idea popped up to start this, “The Workbench” category. Afterwards I asked @thebaldgeek to create this category and he did (thank you!). I will share more of my finds in the future and hope you all will too!

A little bit of extra info with for the SMA connectors:

SMA connectors are rated for up to 500 mating cycles, but to achieve this it is necessary to properly torque the connector when making the connection. A 5⁄16 inch torque wrench is required for this, set to 3–5 in·lbf (0.3 to 0.6 N·m) for brass, and 7–10 in·lbf (0.8 to 1.1 N·m) for stainless steel connectors.
Source: SMA connector - Wikipedia

I use both brass and stainless-steel connectors, so I decided to buy a separate wrench for each of them. In this case there is no need to adjust the amount of torque needed.

As always AliExpress is a great source for buying affordable stuff like this. Of course, it will probably not compare to truly professional gear, but in that scenario, the price range is not comparable. The brand I bought is called MXITA and they seem to have an Official Store, on AliExpress. Disclaimer: I’m not affiliated or endorsed by them so please do your own research.

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@thebaldgeek just made me laugh on the Discord with his photo and the torque wrench.

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Not great for tightening baldgeek heads, but awsome on SMAs…

Till @ewesterlaak original post, I did not know these were a thing and now that I have one and have used it a bit, I’m ashamed it took me 10 months to buy one from reading his original post.

I got it off Amazon USA. Usual 2 day postage.
Most of my SMAs are brass, but worth keeping in mind that stainless steel SMA’s have a different torque specification.

One of the comments on Amazon said to be sure to use the included oil to lube the wrench before using it, there was no included oil, so I am not sure how to process that, it seems very smooth with some traces of light machine oil on the moving bits already.

I messed about on the work bench with some assorted SMAs before putting it to use on my C-Band setup.

There is a hex nut in the top that could (I presume) be used to set (calibrate) the actual torque, for now, leaving it untouched.

I clearly have not be torquing up my SMA’s tight enough by doing them finger tight, this is the immediate observation. The wrench goes much tighter. I also like how consistent it is. No question that cold fingers (on the roof in winter for example) vs summer at ground level would result in vastly different tensions on the SMA. With the wrench, no matter the ambient temperature, the SMAs will always be the same.

If there is any downside, it would be that any SMAs done up with this wrench are going to be impossible to undo with human fingers. Going to need to remember to take it on every trip to the roof.

Long review short. If you are doing any experimenting or changing around of setups that use SMA connectors, get one.

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Spent a few minutes up a ladder to run the wrench over the L-Band feed.

Sort of gives a better idea of the size and how it could be a bit tricky to use in a confined space like an enclosure for example. Some forward planning on those sort of tight builds will go a long way, but I still think its well worth using the wrench to know that each connector is correctly torqued up.

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Since we all seem to have stepped up our game here by using torque wrenches lately and I got a new VNA capable of pretty precise measurements that will even show errors in calibration due to connector torque, I decided to summarize the best available information from my paper library and the intertubes and try to comb out the minor differences in recommendations I spotted among the cited sources.

In my web travels looking for best practices for doing 2 port SOLT VNA calibration, I came across a 2022 Anritsu Guide for connecting DUTs to VNAs and the proper use of torque wrenches to enable repeatable VNA measurements. I was surprised that there were correct and incorrect ways to hold a torque wrench and align a torque wrench at a less than 90 degree angle to the holding wrench. I’ve attached an abridged version of that document here. and my Table of Recommended Torques.
Lothars Torque Guide.pdf (1.1 MB)

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