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

[John Spigel]

And, for us today, adding to the permutation mix of possible settings 
you need to include along with AM/FM, USB and LSB.  With some mix of 
combinations, not necessarily the same, we can talk to each other. The 
Dovetron Tempest I'm playing with had an AFSK output which initially I 
set for Mark Low, Space High with normal operation LSB.  But on the net 
last Saturday I needed to copy in REV, because the other side of the QSO 
needed to go to REV to copy me and we are on USB! We could copy, but, 
unless told, what I think are correct settings are not! I could of 
course flip the Mark and Space with the front M/S frequency dials, but 
that would add to my confusion.  So in the interim I've added a switch 
on my Dovetron rear panel to flip High/Low for my loop generated Tx 
signal to give me that option and let others in the group copy and  
transmit "Normally" and for me to determine what is NORMAL. I'll 
probably also need to keep a cheat sheet!
73, John W1AN


On 08-Mar-24 13:27, 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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