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Re: [TowerTalk] Reliability (or not) of SMA connectors

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Reliability (or not) of SMA connectors
From: "Lux, Jim" <jim@luxfamily.com>
Date: Sun, 4 Dec 2022 10:25:53 -0800
List-post: <mailto:towertalk@contesting.com>
On 12/4/22 6:05 AM, Pete Smith N4ZR wrote:
I'm not sure if this is the right place or not, but thought I'd ask because this is at least a feedline question.

I have a number of SMA connectors in areas of my station like my RBN SDR and my N1MM Spectrum Display.  It seems like every few weeks I start running into problems, and have to go through and retighten them to get rid of intermittent signal losses.  Is there anything that can be done to secure them better?

If torqued to 5-8 in-lb they shouldn't be loosening.  That's definitely more than finger tight, and pretty "snug" with a small open end wrench. The usual "ignition wrench" is about 4" long, so 1-1.5 lbs force on it. If you've got a small scale (e.g. kitchen) you can feel what 1 pound of push is like, and go from there. Or, if you can buy or borrow a real SMA torque wrench, you'll get the feel.


They're about $150 for the real thing that comes calibrated from the factory.  About $50 from some random 6 letter company on Amazon.  There is a spring assembly inside them that needs to be periodically calibrated ( I don't know how fast these things go "out of cal" - it's a spring, it's way less than the spring's ultimate yield, so it should last forever)


I suppose one could "stake" it with some removable polymer (nail polish, model airplane glue, glyptal) after tightening. A tiny dab on the edge will keep it from loosening and is still breakable with a wrench to remove it.

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