Observatoire Neuchatel (HBG) :

 

listen to the sound - only the phase modulated second pulses, no ID (Nils Schiffhauer)
here a screenshot of the signal from a spectrum receiver, showing RBU (66,66 kHz), HBG (75 kHz), and DCF77 (77,5 kHz) (rb, 2009)

in 1964, the 5 MHz outlet was still active, and was QSLed by Maarten van Delft. Maybe this letter from DIZ Nauen helped identifying?
here a letter, from the early 1970's, giving some technical details (Rudy van Dalen)
this letter verifies the time signal transmitted via the swiss broadcasting station (Willi Passmann, 1977)
a beautiful card from the operating agency (Mauro Giroletti, 2009)

visit the official web-site

 

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Callsigns:
HBG
HBN

 

Frequencies Morse Telegraphy:
75
5000