I’ll point out that a common method of detecting bugs at the time was to set up a radio receiver with a speaker and then sweep the frequency, if you managed to hit you would get a feedback sound between the speaker and bug. These oddball modulation schemes would prevent that from working.
I like it a lot that many of techniques have a hybrid analog/digital structure that would involve sample-and-hold, sweeps and comparators like the Triple Pulse scheme.
Today I can’t believe you wouldn’t use some digital solution but at that point in time you’d be lucky to be able to use a small IC.
Audio ADCs are incredibly small and the digital functionality needed isn't much for this. One can fit everything in a sub mm2 IC I think. Minus the antenna.
They were doing all that in the 1970s. There was a sense of panic about electronic eavesdropping around the Watergate period, where it wasn't just Nixon, but really every private eye knew some kid who knew how to make bugs with a few transistors. It got talked about in a lot of books from this time period such as
which was a scandal with many dimensions including the author of that book getting busted for insider trading, there was an incident where the management of that company set up bugs in a room where auditors were working so they had some idea of what the auditors were looking at so they possibly trick them.
That web site has some articles where they talk about fabrication techniques the CIA was using for bugs and it seemed they weren't using ICs but rather trying to miniaturize discrete component designs as much they could just as IBM was doing for the digital electronics for the System 360.
I'd assume if you were doing it now you'd use some kind of pure digital scheme with an ADC, encryption and spread-spectrum modulation of some kind. I still have a sweet spot for things like sample-and-hold, PLLs, and such though.
I like it a lot that many of techniques have a hybrid analog/digital structure that would involve sample-and-hold, sweeps and comparators like the Triple Pulse scheme.
Today I can’t believe you wouldn’t use some digital solution but at that point in time you’d be lucky to be able to use a small IC.