John P wrote:

I monitor VLF and have discovered a data signal at 300.0 KHz. It seems to
be on continuously. I have searched the FCC databases and searched the
web,
but can not find out what this signal is. It is S9+10 in Maryland.

Can anyone tell me what this is or where I can search for info to try to
identify it?

Are you near any high voltage transmission lines? Power companies use power
line carrier to pass low bandwidth telemetry and relaying signals on
transmission lines. They typically operate from about 300 kHz down.

--
budr at netride dot net