No, this page isn’t about jazz musicians getting together after hours to play for their own pleasure and enlightenment far into the night. It’s something more sinister!
It’s to do with how you block out an undesired radio transmission. You can’t actually ‘neutralise’ it, as such… what you have to do is transmit another powerful signal on the same frequency from as near as possible to the enemy transmitter, which will overlay and render the original signal incomprehensible. Assuming this original signal was speech, your success in obscuring it is very much enhanced by what you transmit. If you were to transmit a single tone for example, people might be able to ignore it & still hear the original signal, albeit less satisfactorily.
What we need is some broad-band noise or variable-tone signal to truly make a mess of what is underneath. I daresay there’s quite a bit of ‘Jamming’ still going on now, but the four samples of it you can hear on this page are quite old, as they date from the 1940s, and probably during & after WW2 (1939 – 1945). They were almost certainly recorded off the air; the discs are 10” (25cm) shellac pressings.
There doesn’t seem to be any programme material underneath… this would make sense; if you wanted to study the jamming signal, you would want it ‘by itself’, not jumbled and garbled together with whatever it was supposed to be blotting out. So these discs were presumably recorded after the underlying transmission had ceased… or of course, before it had started. Any information as to date, source, frequencies they were used on, would be much appreciated and will of course be added here.
How do I come to have these two examples of radio arcana? The answer is prosaic in the extreme: I found them in a junk shop here in Birmingham, some time in the 1960s. Each label below has an audio bar which will play you about 15 seconds of the disc.
Incidentally, I did play one of these back in the 1980s to a retired Major of the Royal Signal Corps, who exclaimed “Good heavens – I’ve not heard that sound for 40 years!” (I wrote that sentence in 2002. It seemed OK at the time; but re-reading it in 2019 it seems vaguely unsatisfactory. What was he supposed to say? ‘Great Scott! I’ve never heard that before in my life.’? Of course not. Therefore the sentence is, essentially, redundant; as is, I freely admit, the majoriy of what I write…)
Page rewritten 17th September 2002.
Re-formatted 29th October 2017.
Revised 30th June 2019.