[TowerTalk] Reliability (or not) of SMA connectors

[Lux, Jim]

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.