Ah....memories...!!

In my early days (nights?) at the BBC, we did indeed close down our networks overnight, the process (for MF transmitters) involved at least 4 minutes of Silence on the lines feeding the beasts, which triggered the off switch all over the country..
To keep our Transmitter colleagues amused overnight (and to keep them away from the sheep!) Each Network had what we called Pulse or Bong tone sent down the lines to prove that they still existed.!

Radio 1 660 Hz
Radio 2 440 Hz
Radio 3 200 Hz
Radio 4 900 Hz

These bongs where not enough to wake up the Transmitters.
That was done manually (or once a year...Old Joke!) by yours truly, at some ungodly hour with a 4 minute burst of steady 440 Hz.

This must be what Bob D is referring to....
Of course nowadays, such satanic nightly rituals, along with the Test Card are just a distant memory...Ah Well...

A nostalgic Ralphie dreaming of happier halcyon days...

Next time children, a description of the mind altering properties of Negative Pips!

All of which of course has nothing to do with the original question, about whitch, I haven't a clue...Sorry !!!!