[TheOtherHobbes]

I'm finding it hard to imagine no one noticed an intermittent 1kW at 330MHz from somewhere close.

[unnouinceput]

Well, the article does say a radio-amateur stumbled upon it and alerted the embassy. So in the end someone did. Since Soviets did the surveillance on key moments, and not continuous, that's what enabled for device to remain undetected for so long