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

[Duncan Brown]

The decision as probably made by someone who had never operated RTTY/RATT !

73,

Duncan
K2OEQ

On 08-Mar-24 08:27, John Vendely wrote:
> 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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