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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