My pet theory is that this phenomenon was caused by an adversary deliberately beaming high-intensity microwaves into the embassy to excite passive / resonant audio listening devices hidden inside. Such devices consist of a hollow metal cavity tuned to resonate at a particular microwave frequency and acoustically connected to the nearby air by a thin wall that serves as a diaphragm; sound causes the diaphragm to vibrate, which slightly changes the resonant frequency of the cavity, thereby modulating the amount it “rings” in response to the external microwave source. Separate receivers can be set up to listen for the “ring” signal and their recordings analyzed to recover the audio, i.e. the conversations going on inside. Such devices have the distinct advantage, for a long-running surveillance operation, of requiring no internal power source. Their use by Russian security forces came to light in the early 80s when one–called “the thing” because nobody understood what it was at first–was discovered concealed inside a wooden carving in the US embassy in Moscow. That device is I believe now on display at the NSA’s Fort Meade museum.
Recently, I went to a seminar for retired engineers hosted by the IEEE in San Antonio, home of Southwest Research Institute, long one of the US government’s go-to private connectors for security-sensitive technical problems. Sitting across from me, beside his wife of 50 years, was a retired EE from SWRI who, it came out in conversation, spent much of the 1970s working on detecting North Korean infiltration tunnels by analyzing signals from radar tranceivers dropped down boreholes on the South side of the DMZ.
When the Moscow embassy bugging scandal broke, this man was assigned to the team that eventually figured out what “the thing” was and how it worked. In the course of that work, he collected and analyzed reports of a strange “embassy disease” that he and others believed were linked to the months and years-long exposure of embassy personnel to the high-intensity microwave radiation needed to excite these passive listening devices.
