As one or two people have said, modern radars are not so susceptible to electronic quirks. In the mid sixties, the CPN 18 at Wittering was very prone to what appeared to be extremely high speed primary returns. These were identical in all respects to the returns from the then resident Victors, apart from the speed of course. The only give-away was that these targets always spiralled directly towards, or away from the overhead. Nobody who has spent time at Wittering could ever imagine alien ships deliberately targetting the place.
By the way Minesapint, I was at Northern Radar in the early 70's, and the overhead was respectably small for a long range radar. Unlike Midland Radar of course, whose infamous overhead (according to an Able-Lable) extended as far as Hong Kong.