This series started with https://k9zw.wordpress.com/2019/09/10/im-a-ham-or-am-i/
Protecting your Digital Signature as an Amateur Radio Operator is a rather complex and esoteric area for most radio amateurs.
To keep this article simple I will avoid getting into the technical reasons what your Digital Signature looks like or why it is often exposed.
Digital Signature can be likened to the radio equivalent of a “finger print” – first there is the general smudge of a print, perhaps where not expected, and then with analysis the detail of the print can be used to identify the person it came from.
RDF (Radio Direction Finding) is another aspect, one that deserves separate discussions.
Both your Transmitter AND your Receiver have Digital Signatures. Some of your other gear may also have a Digital Signature (routers, computers, monitors) but we will focus on your radios.
Specialist gear can sort out which particular piece of gear is in use. In many cases the gear doesn’t have to be specifically transmitting, as most gear has enough low level emissions to identify..
Adding to the fun, your natural voice also has its own unique “finger print” which can be picked out. Some claim that there is enough variation in the sending of Morse Code to also identify a particular operator.
So what are the ways you can mitigate the situation?
Against a dedicated effort to find and identify your station, perhaps not much.
But there are some techniques that will draw down the exposure.
Gear-Off, disconnected and shielded when not in use – these simple steps will largely mitigate the non-use exposure. Some trainers recommend ammo cans or other near Faraday Cage storage, fully deenergized and disconnected of course. The idea is your not-in-use gear cannot be resonated or otherwise identified.
In this vein antennas will be a concern, though training is usually not very complete on what to do about antennas and feedlines.
Operate-Displaced – this usually considers your gear as something that would be “given up” rather than “defended” by physical distancing. If your gear allows it and the internet will allow for a VPN to station, you could be anywhere operating stationary stations.
Transmit and Run – here being the idea that after short transmissions you move your station prior to being RDF and Identified. Against a professional team you will be trading their speed against your speed, and as for Identifying most likely they have that very quickly anyway. To make a run you may have to leave your antenna and even feedline (or other hard to disassemble gear) making a sort of hybrid with “Operate-Displaced.”
Mask your Digital Signature – added processing and circuitry can obscure the unique identifiers. Some training suggests using text-to-speech to use synthetic voicing for phone operations, under the premise that unique identifiers are not known to be carried by these computer voices.
Rotate between Resources – using several stations and several speakers for phone, or several programs for digital. Change it up enough, recognizing that while those opposing you may figure some of it out, the variety makes their analysis (especially automated analysis) less straight forward.
Use the Signature to Advantage – If you watched the movie “V is for Vendetta” the protagonists all wore the same masks, making it hard to pick out any one individual. Replicating your Digital Signature across several stations could similarly be effective.