Please bear in mind that the actual torque value depends on the type of
connector and the application, and that over torque can make problems,
too. For SMA, brass connectors should be torqued between 3-5 in-lbs,
while stainless SMA connectors should get 7-10 in-lbs. Also, the usage
is a consideration. For lab/engineering (or shack) use where the
connector is likely to be disconnected, a lower value should be used.
For a final, permanent, installation, a higher value should be used. I
had an instance of an SMA torqued to 8 in-lbs on an assembly with
replaceable screw-in receptacles, and attempting to remove the plug
resulted in the receptacle coming off the assembly. Since this was for
lab/engineering use, we replaced our 8 in-lbs torque wrench with a 4
in-lbs wrench and had no further problems.
Another problem I have seen a few times with stainless connectors is
galling, which can ruin a connector. For engineering use, I prefer brass
(sometimes gold plated) connectors for this reason. I have thought
about applying a stainless anti-galling compound to stainless SMAs, but
I think a more common problem I have seen is cross-theading or other
damage due to forcing the coupling nut with the wrench when the
connectors are misaligned. I prefer to carefully attach to full finger
tight before using the wrench. I assume that if the coupling nut
becomes difficult to turn with my fingers before the connector is fully
engaged, the connector is likely misaligned or damaged.
Here is a link for further reading:
https://www.microwaves101.com/encyclopedias/connector-torque
73,
Avery, WB4RTP
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