SMA connectors

[Grandchuck]

I was wondering about SMA life expectancy and ran across this on the web:

"The mating cycle of an SMA connector refers to the number of times it can be connected and disconnected without compromising performance. A typical SMA connector can withstand over 500 mating cycles. Factors like design, material quality, and manufacturing precision influence this durability."

In addition, one should not allow rotation of the male pin during mating.   I think this number (500) might be too high?

Anyway, here is the source:  https://metabeeai.com/rf-connectors/sma-connectors/what-is-an-sma-connector-everything-you-need-to-know.html

Lots of good info there!

[jpanhalt]

That information for all connectors should be readily available.  Several years ago, I was looking for small charger and programming connectors.  Of course, I wanted two different styles.  USB miniature and micro sizes (USB C was not so ubiquitous then) had numbers in the thousands, while pin and sockets were much lower; some assemblies were only 10 cycles.   For some of those connectors, it was a hassle getting that information.  I think it ought to be right up there with pin number or current capacity.

[coppice]

SMA connectors vary enormously. With some you are lucky to successfully mate them just once. Others go on in test applications, being mated and removed, for years.

[Solder_Junkie]

You can use a male/female adapter to save wear and tear on the SMA socket on your instrument.

Don’t forget to tighten SMA plugs with a torque spanner. The correct setting is 0.5 Nm, dedicated SMA torque spanners by Xite cost around $30. In the UK, SDR-Kits stock them.
https://www.sdr-kits.net/Torque-Wrench

SJ

[radiolistener]

You can use a male/female adapter to save wear and tear on the SMA socket on your instrument.

But note that adding SMA adapter add some signal loss and leads to worse SNR, so, you're adding additional element for signal path. You can see reflections on every connector and adapter with time domain reflectometer.

[Batavian]

Late to this thread, here are my thoughts:

500 mating cycles is optimistic for most SMA connectors. The mechanical nut can keep on screwing on and off for thousands of cycles, but the RF properties have long since degraded. 500 cycles may apply to some SMA connectors from better manufacturers, at low frequencies but that is "maybe" and we should get that in writing, on the specification sheet (parol evidence rule). Verbal assurances are inadequate. For example, if we have an application at 6 GHz and need a large number of mating cycles, we should consider a better manufacturer and guaranteed in-spec operation to at least 18 GHz.

Brass body SMA connectors are convenient but susceptible to deformation, to becoming deformed under a single application of the 0.9 N-m torque wrench. This applies to many convenient surface mount SMA connectors. Any RF lab should have both 5 in-lb / 0.57 N-m and 8 in-lb / 0.9 N-m SMA torque wrenches.

SMA mating cycles depend a lot on the integrity of materials (both the metal and the dielectric), plating type uniformity and thickness, and both manufacturing QA and machining tolerances. To reduce material cost, some manufacturers use recycled teflon as dielectric: recycled teflon isn't such a good dielectric. I recommend routine incoming inspection of new connectors using a stereo or trinocular inspection microscope. We can see a lot if we bother to look. We can see things that knockoff vendors assume we will never look at. Good practice is to avoid the cheapest possible connectors, and purchase new SMA connectors made by well regarded manufacturers such as Cinch, Amphenol SV Microwave, Huber+Suhner, Pasternack, Fairview Microwave, Wurth etc. We don't need the most expensive SMA connector to make a good project, we just have to avoid the cheapest and the ones with significant manufacturing defects.

My rule of thumb for longer connector useful life is to use stainless steel SMA connectors, and for prototyping and development use 5 in-lb / 0.57 N-m breaking torque because I want multiple uses without performance degradation. When shipping a product with stainless steel SMA connectors, I use 8 in-lb / 0.9 N-m (Cinch Johnson brand gold-colored torque wrench). For a quality 18 GHz stainless steel SMA connector, we can often get 20 (twenty) mate cycles for properly applied 8 in-lb / 0.9 N-m torque without degradation, still within electrical specifications at 18 GHz after 20 mate cycles. The connector will remain in-spec at lower frequencies for more cycles. AFAIK we don't see 500 cycles at 18 GHz.

For brass SMA shells, we should only use 5 in-lb / 0.57 N-m (for example, the Cinch Johnson brand blue-colored torque wrench).  Not sure of the in-spec number of mate cycles for average brass SMA shells.

[DataStorageIC]

500 mating cycles doesn't sound unusually high for a properly made SMA connector, but I wouldn't treat it as a universal number for every SMA on the market.

For example, some reputable manufacturers specify around 500 mating cycles for standard SMA interfaces. In practice, connector life depends heavily on interface quality, alignment, cleanliness, torque and how often the center contacts are allowed to rotate during mating.

For test equipment, I would also use a connector saver / male-female adapter if the port is going to be connected frequently. Replacing an adapter is much cheaper than replacing a damaged instrument connector.

I think the biggest difference is between a properly specified RF connector and a low-cost connector with unknown interface tolerances. Both may be called “SMA”, but their practical mating life can be very different.

[coromonadalix]

you have quality in theses,  metal thickness,  some china crap are not fully in specs, and are brittle,  they will snap if you slightly over torque them, and the gold plating too


i use them a lot in our equipments, aroung 2 - 2.5 Ghz  signals,   my rules is around 300 ...  and the cabling used in them "if you hand made / diy them", or "buy already made" play an important role ... capacitance, impedance, signal losses ...

on the DIY one(s)   we use a spectrum analyzer to see the losses over x or x lenghts, and im generally  pretty darn straight on the line, some signal db losses over the lenght,  but darn straight ..  rg316, rg226  ...

and yes  connector savers are a must,  spectrum analyzers, scopes, signal generators ...  many males to females ones in stock.

[nonius_]

Many years ago I was reading the datasheet for an SMA-connector and was shocked to read that it was actually only specified for 10 (!) mating cycles.

[Randy222]

I am curious. Teflon as a washer in compression clamp is not good as the teflon squishes over time.

If you torque an adapter to the equipment to save the conductor mating from permanent damage, how long until the adapter yields in a negative way? You cannot just go back with a torque wrench due to static friction (to check it), the only way to properly torque is to start below ~80% and then finish to 100% in one motion.

So is there a general to-do to back off the adapter and re-torque it, like do that once per 100 connections? Do you have a log book?