nanoVNA-H – coax connectors

The NanoVNA uses PCB end launch SMA connectors, and if one is tightened to anywhere near the SMA specification torque of 1Nm, the assembly is ‘soft' as the board flexes… a warning that this may cause damage (track cracking or outright separation of the SMA connector).

If you have a bare board, you can counter this torque with a wrench applied across the flats of the female connector, but in my -H, it is fitted in a plastic case and the flats are not accessible.

For my own use, I have fitted a 10dB attenuator to Port 2 (to improve Port 2 Insertion VSWR), and an SMA saver to Port 1. The PCB was removed from the case and these components were torqued to 1Nm as described above. The case was reinstalled and these parts are regarded as permanent fixtures.

Obviously it is still not possible to torque the connectors to 1Nm, a disadvantage of the PCB design.

I replaced the low grade coax tails supplied with the -H with a pair of 500mm RG400 cables which are robust, and test with close to specification matched line loss (differently to the supplied cables).