I think this may be the source:

73.6  CFH Naval-Halifax (Mill Cove), NS, Canada (FSK 75 Bd)

Above found at:

http://www.provcomm.net/pages/joe/introvlf.htm#Target Frequencies below
100Khz

Dexter



Dexter McIntyre W4DEX wrote:

The RTTY signal I recorded a few days ago is now extremely strong in
North Carolina at 2300 UTC.  As Stewart told me the shift is 75 Hz.  I
have both Spectran and wav file saved if anyone is interested.

Dexter