I would like to emphasize on the point Jim made: As long as you have an USB cable running into the antenna's near field, it will affect the measurement, even if an USB isolator or an RF isolation transformer is used. Also any isolator or transformer has capacitance, and even if it's just a few pF, this might be enough to cause an unacceptable measurement error in some cases.

So I think that the best thing to do is to connect the NanoVNA directly to the antenna, powered by its battery, and use any small battery-powered device to translate between USB and a fiber optic cable. Then run that fiber cable down outside the near field of the antenna, and interface it to the readout software.

As an alternative a radio link could be used. On Wifi or similar.

If suitable low-cost converters can't be found, it should be simple enough to write a program for an Arduino, to convert between USB and fiber, or use an ESP32 with its built-in WiFi. In fact, given how easy it is to use WiFi with the ESP32, it looks like the way to go!

With an ESP32 plus battery attached to the NanoVNA, there is just the capacitance of this small pack to the surroundings, and that should be really negligible on HF. But on VHF and higher even this is enough to significantly affect the measurements.


Manfred