Here is an interesting relic from the Cold War era,
the DRUGA-3, aka the
Russian Woodpecker. Apparently it was part of an early warning system for ballistic missiles.
Starting in 1976 a new and powerful radio signal was detected worldwide, and quickly dubbed the Woodpecker by amateur radio operators. Transmission power on some woodpecker transmitters was estimated to be as high as 10 MW Equivalent isotropically radiated power.
An interesting post on this subject.
Here is what it sounded like:
I'm interested to ask oldskool ham operators if they know where I could find more audio samples? It's very intriguing. I would love to do some basic analysis of these signals.
Have you come across the conet project
http://en.wikipedia.org/wiki/The_Conet_Project ? It has recordings of stuff like that amongst the numbers stations, "The Buzzer" sounds like the kind of thing you're interested in , I tried to upload it here but it's too big, I can upload it somewhere else if you're interested
Oh nice! Do you have a
dropbox account? It provides several GB of online storage for free and able to share some files publicly.
That looks like a huge antenna. How big must a 1kHz antenna with decent continental coverage be?
I've been listening to some of the samples, I swear, I heard one of them before in a Boards of Canada album!