Cuban "M8" Transmitter Problem

This severe malfunction has been heard several times during CW Morse code broadcasts of the Cuban Cut Numbers Station, ENIGMA designator M8, which uses the letters ANDUWRIGMT as a brevity substitution for the digits 1 through 0. Ordinarily, this station has a killer signal into the U.S., and Radio Havana transmitters are strongly suspected.

Close examination shows that the CW keying has no shaping whatsoever, and is being completely interrupted at the AC powerline rate of 60 Hz! The resulting square waves show harmonics out to at least 10 kHz, causing some truly awesome splatter.

Given that morse audio tone keying often shows up on Cuban voice frequencies, I strongly suspect that this tone actually keys the transmitters when M8 is broadcast. If so, they have one hell of a hum.