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Audio Masking

145 points by goles

by PaulHoule

2 subcomments

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.

by somat

0 subcomment

Also of interest in this domain.
The great seal bug(The Thing)
https://www.youtube.com/watch?v=NLDpWrwijE8 (Machining and Microwaves)
What I like about this specific video is that the guy actually builds one. And there is a world of difference between a popular article on how the thing worked. and the subtle genius engineering required to get it to actually work.

by fortran77

2 subcomments

Today with spread spectrum, it's probably much easier to hide a covert radio signal.

by motohagiography

0 subcomment

it would be interesting to see what the waterfall charts of these looked like, and I can't tell if there is enough info in the article to produce a gnuradio flowgraph for any of them. it could be a fun retro spy tech project.

by amelius

1 subcomments

In practice most audio channels are low-pass filtered and bandwidth limited, so I'm guessing that these modulation techniques are not going to work. Also, we have digital methods now.

by squarefoot

0 subcomment

Oh crap... the Scanlock Mark VB receiver shown on that picture is really similar to the Autolock 7 receiver I snatched at a flea market for a song many years ago, and after finding absolutely nothing about it online sold it on Ebay for like 3 songs. Had I known it was a bug finding device I could have donated it to the Cryptomuseum.