[TowerTalk] Reliability (or not) of SMA connectors

[Michael Tope]

Geo, you make an important point about the purpose of the adhesive blob 
that bridges the male connector nut to the threaded portion of the 
female connector. I have seen it used that way in all the space hardware 
that I've worked on (as well as on fastener heads). I've heard it 
claimed that this strictly for inspection purposes (i.e. did the torqued 
connector nut move after the unit was subjected to a launch level 
vibration test?) and that it provides no significant holding power. I am 
not sure I believe that, but non-withstanding it's contribution to 
connector nut locking, it certainly does serve as an inspection aid.

When doing tests at work where RF phase stability is paramount, loose 
connectors can show up as noise in the test data, so I make a big fuss 
about making sure all the RF connectors are properly tightened. The 
other thing I fuss over is making sure cables are properly strained 
relieved. SMA connectors are small, so if the cable is heavy and/or 
stiff it can easily impart enough torque on the SMA connector to loosen 
it when things are being moved around or just from gravity. When using 
SMA connectors in a ham shack, paying attention to those two things 
without having to resort to adhesive staking should suffice in most if 
not all cases.

73, Mike W4EF...............

On 12/4/2022 3:44 PM, GEO Badger via TowerTalk wrote:
>   Do not put any adhesive on the threads. Do get a torque wrench, they won't go out of spec in your lifetime, or a 5/15" wrench to dedicate to your SMA use. Or a SMA finger wrench, https://www.rfcafe.com/miscellany/homepage-archive/2014/SMA-Finger-Wrench-Bracke-Manufacturing.htm, that slips over the nut and you tighten/loosen the connector. They are available in plastic or brass. It's difficult to over torque a SMA connector, if you're not ham handed. These connectors are in use in major hi-reliability applications and they do not come loose with proper application. BTW, there are SMA push-on connectors for the test environment. Also M and N push-ons.
> As pointed out, the shield connection is the interior face of the connector, not through the nut. Once the assemblies are interconnected, they should not be moved about unless connected by a very flexible coax.
> After the final assembly on can put a dab of Sentry-Seal on the connector where the threads are visible. This doesn't prevent loosening but will notify the operator if the connection has failed or been tampered with.
> Geo, who may or may not have used a bunch of SMA connectors and their derivatives in a past professional life, and sold connectors for M/A-COM Omni-Spectra, who I believe originally developed the SMA.
> ---
> Ciao baby, catch you on the flip side
> 73 de W3AB/GEOAFA9GB
> WA2LSI, KE6RJW, W6B, W7B, AAR9AG
> http://www.w3ab.org
>
>
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