There are identical carrier signals on 6993 kHz and 4443 kHz that I've heard for the past 5 years or more. I've never heard any intelligence associated with these signals.
Each signal is actually three carriers 10 Hertz apart, best seen on a waterfall display.
On either frequency (6993 kHz or 4443 kHz), the signal will appear to warble: this is because each of the three carrier signals (10 Hz apart from each other) will fade at a different time as if the carrier signals are either not from the same antenna, not from same location, or each carrier is beamed to in a different direction.
I live in central Florida and can usually hear one or other signal at all times of the day during any month of the year.
I hear the 6993 kHz signal midday suggesting it's in the southeast USA or Caribbean perhaps. At night, I heard both signals with the 6993 kHz signal being stronger.
If anyone has information of these mysterious signals, or has 40 meter directional antennas that can perhaps provide beam headings, maybe we can figure out where they are.
Dave