SMA essentials

SMA connectors fall into the category of coax connectors that depend on proper torque of the retaining nut to ensure adequate electrical contact of the shield, ie proper connector performance.

Correct tensioning of connectors is vital to accurate measurments, especially when using a VNA.

Fig 1:

Above is a small collection of tools for working with SMA connectors. The tools from top to bottom are top and bottom are:

An 8mm torque wrench for accessing SMA connectors that are crowded together;
a 5.5mm combination spanner for SMA F-F adapters;
an 8mm combination spanner for SMA connector nuts;
an 8mm combination spanner for SMA connector nuts (you really need a pair);
an 8mm torque wrench for SMA connector nuts.

The 5.5mm spanner can be hard to find, it seems that most manufacturers don't make metric spanners below 6mm though 5.5mm is the ISO standard size for nuts for 3mm thread. 7/32" AF and 5/16" AF respectively may be suitable inch size substitutes. Ebay can be a good source for these small tools, (1) came from the manufacturer in the US, (2)-(4) from a UK Ebay seller, and (5) from an local online store. (Search on Ebay for "5.5mm combination" to find a source for items 2-4.)