From Dave G3YMC

The RTTY signal which has reappeared on or around 137kHz is the self same
signal we were discussing in January and at various other times.  It
appears for a few days at a time and then disappears for a month or so.  It
has the definite characteristics of a transatlantic signal, being inaudible
during the day, appearing in the late evening and being quite strong around
dawn.  It disappears around one hour after dawn, although I have heard it
rather later in the morning and once in the mid afternoon.  Very
characteristic of US amateur signals on 160m.

When I surmised a while back that it may be transatlantic, this was largely
dismissed.  Perhaps our USA members should make efforts to establish its
location.  It appears to transmit at various times RTTY and FAX.

73s Dave G3YMC