I don't know, but Wikipedia has a good example of a NLJD countermeasure introduced in the 60s: https://en.wikipedia.org/wiki/Nonlinear_junction_detector#Counte

I don't know, but Wikipedia has a good example of a NLJD countermeasure introduced in the 60s: https://en.wikipedia.org/wiki/Nonlinear_junction_detector#Countermeasure https://en.wikipedia.org/wiki/Nonlinear_junction_detector#Co... (specifically the CIA's SRT-107: http://www.cryptomuseum.com/covert/bugs/ec/srt107/index.htm http://www.cryptomuseum.com/covert/bugs/ec/srt107/index.htm) As an aside, the entire website for that second link is pretty interesting.