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

[John Vendely]

Hey Nick,

The reason for various military branches switching from MARK high to 
MARK low is surely one of the world's great mysteries, on par with the 
construction of the pyramids.  From an engineering perspective, the 
choice is entirely arbitrary, but so far as I can see, prior to the U.S. 
Army's introduction of the MD-522 in 1967, MARK high was the 
convention.  So why change?  This must have been a bit confusing at 
times for Army RATT operators, since their existing GRC-26 and GRC-46 
equipment was MARK high...

73,

John K9WT

On 3/7/2024 1:16 PM, Nick England wrote:
> 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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