Shortwave Interval Signals
See https://sites.google.com/site/g3xbmqrp3/hf/interval .
For a touch of pure nostalgia try the link above. Like many, my first experience with short wave was as an SWL, listening on a simple receiver to some of these broadcasters. Many were trying to indoctrinate me whereas all I was really interested in was a QSL card! I recall some great gifts from China! I heard some impressive DX back in the 1960s.
Of course radio amateur DXing came later and radio amateurs ran considerably less power. These days I regularly copy stations running less than 5W from the other side of the planet, but I can still recall the thrill of hearing a 5kW broadcaster in the Windward Islands and copying Radio Australia on a crystal set – all the way from Australia too!
Thanks for the link(s), Roger, just had a pleasant few minutes remembering hours and hours of listening to these stations. I remember doing the language course Svenska po Radio on Radio Sweden, and had not heard that interval signal from them for over 50 years. On the other links I look forward to hearing Radio Hilversum (the Happy Station), Radio Bucharest, Radio Tirana etc. that got me into trouble when applying for security clearance in the RAF many years ago!