https://www.srcinc.com/what-we-do/ew/crew-duke.html
Lightweight, low power consumption radio frequency scrambler.
We used these in Iraq to keep cell phone triggered IED's from blowing us up.
You could buy a local cellphone on base and a phone card to call home, like an old Nokia style. You could tell when someone entered the base and forgot to shut off their jammer because you couldn't use your phone anywhere within a few hundred yards of when they drove by…