Ken Wilson wrote:
Steve,

There is Aircraft on a Freq of 5.649 mhz USB.Planes flying over the
atlantic They call in & get a SelCal I think they call it????? from
Gander, NewYork, and other land base stations. I think it is called
North Atlantic C or NAT-C

I am not sure the selectivity of your receiver but I doubt this is what
you are hearing.

Sorry not more help.

73, Ken KG4BIG

Georgetown, KY.

Yes, I'd stumbled across this signal because I was monitoring the comms
on 5649 khz. Kept hearing this weird databurst on a nearby frequency
and it turned out to be on 5652. It stopped not too long after I made
my initial post above. Never was able to get clear enough copy on the
speech to figure out what it was.

Steve