no recordings available
the german nautical officer's handbook of 1951 listed it still
as Germany: 'Brüsterort'; so maybe Soviet authorities
took over call 'BT' unchanged from the Nazi authorities, which
were here until 1945.
but besides this strange listing
you should watch the very precise description of the signal transmitted
------------------------------------------------------------
Callsigns:
BT
Frequencies Morse Telegraphy:
291.5
312.5