So this is apparently thought to be a number station (for military cryptography).
A bit of searching leads to
[1] the guy discovering it
[2] a software that can demodulate the signal
[3] that software's manual, which says (from page 28):
> JSM refers to a rather strange signal. The consensus is that it is transmitted by the Japanese navy. When one listens to it in USB mode it normally sounds like a continuous repetitive melody.
...
> With some investigation the symbol rate was determined to be 1500.00 baud. The regular ticking sound was found to be an exactly repeating sequence of symbols. Clearly that serves as a channel probe and frame synchronization pattern.
I don't know, this is not my area of expertise.
But at least from what I've read about other number stations, not all of them are intelligible (e.g. UVB-76 [1])
I should clarify that by “intelligible” I meant that a human can make out the symbols being said (words or numbers) and write them down for later decryption, not that their meaning is readily obvious to people without special knowledge. It sounds like UVB-76's broadcasts (when it's not just buzzing) would be “intelligible” in the sense I was thinking. The Japanese Slot Machine seems like something only machines could work with.
This is way OT but I would highly recommend that anyone travelling to Japan should step into a Pachinko parlour for a few minutes just for the absolute sensory overload. I’m not sure if it’s still as smoky inside them now but back in 2009 it was An Experience.
I played for a few minutes, maybe 100 yen worth of balls. The whole time I couldn’t really even tell if I was winning or losing but eventually my basket was empty!
A bit of searching leads to
[1] the guy discovering it
[2] a software that can demodulate the signal
[3] that software's manual, which says (from page 28):
> JSM refers to a rather strange signal. The consensus is that it is transmitted by the Japanese navy. When one listens to it in USB mode it normally sounds like a continuous repetitive melody. ...
> With some investigation the symbol rate was determined to be 1500.00 baud. The regular ticking sound was found to be an exactly repeating sequence of symbols. Clearly that serves as a channel probe and frame synchronization pattern.
[1] http://www.ominous-valve.com/mystery.html
[2] https://www.saharlow.com/technology/sigmira/
[3] https://www.saharlow.com/technology/sigmira/sigmira_manual.p...