Re: Detector Van existance
So the premise of the episode I saw on One Step Beyond in the 1950s or 60s was based on... what?
The premise of the show, set in the U.S., but I am willing to stipulate that it may have been inspired by UK detector vans, was that a detector van um, detected, a stronger than usual signal, which (Spoiler) turned out to be an alien observer "phoning home" with the day's observations. I was amused but skeptical, but not about the existence of detector vans..
1) "fox and hounds" contests (radio direction finding) had been popular among radio amateurs since before I was born, and in somewhat more sophisticated form for military intelligence in both acts of the Great War.
2) Detecting the intermediate frequency of a Superheterodyne receiver would indicate that a receiver was operating to a particular standard. That is, looking in the 30-45 MHz area (depending on local TV modulation standards) would "find" televison receivers, but ignore audio receivers for AM (typ 455kHz) and FM (typ 10.7 MHz) receivers.
3) In principle, such a van would be quite feasible, although before the retirement of analog TV, I'd expect them to be operated by Cable TV providers or market survey companies.
4) That said, I don't recall if the show mention the signal being a _lot_ stronger than typical IF leakage, let alone "right side up" in spectrum as opposed to the normal spectrum inversion in a typical TV. That said, Outer Limits was not really a "learn to be a nerd" channel. I doubt that later shows like Star Trek made anybody believed one could create a "Universal Translator" from a painted cardboard tube, nor would they waste time including a cobbled up "technical explanation". McGyver bent the laws of physics more.
Anyway, I don't find the concept of a detector van absurd. Yes, FUD is also a possibility, but for me the take-away from the show was "Hey, if you want to communicate less obviously, unused TV channels are a good place to hide".