[GreenKeys] Military Mark High to Mark Low change - FWIW

[Nick England]

>From a 1989 Coast Guard Manual -

CV-3883/UG Converter Keyer AFSK Frequency Adjustment Information
If you have ever aligned a CV-3883/UG Dovetron you probably noticed the
absence of Navy and Coast Guard frequency shift information. Το complicate
matters, prior to about 1972 the Navy's Normal mode of operation was wide
shift RATT with the MARK tone HIGH and the SPACE tone LOW.
The Navy made Reverse keying MARK tone LOW and SPACE tone HIGH the normal
mode of operation in 1972 but stayed with wide shift. On existing signal
conversion equipment radio operators would put the RATT converter in the
REVERSE mode to correct the output logic of the received now MARK LOW
signals.
Technical manuals for older Navy equipment reflect the original Mark High
Space Low convention e.g. the CV-2460/SGC. Manuals for newer equipment e.g.
the AN/URA-17E reflect the Mark Low convention.
The Coast Guard uses Space High Mark Low narrow shift keying as its normal
mode of operation. Some old timers argue that this is REVERSE keying, but
the bottom line is that Mark Low is the standard to which we align our
CV-3883/UG in the Normal mode of operation.
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