[GreenKeys] ZCZC and NNNN

[Sheldon Daitch]

Jim,

If I might add.

ZCZC and NNNN should not occur in any typical text and
would not show up as false letter patterns.

In our old torn-tape days, we used NNNN as the end of
message letter grouping, but I'd suppose that the
M-28 stunt box could have equally been coded for any
other letter group.  Seems to me, tho, that the 
reperfs were set to actually stop on three Ns, but the
4th N was sent in the message, to insure 3 sequential
Ns were received (at least on HF RTTY).  

When we ran the HF RTTY for VOA traffic, we used
FAXFAX to start the tape punch and NNNN to end a
tape (adjusted as I mentioned above).  The ZCZC is
more a military function, I think.  

Of course, today, FAX is a usual abbreviation for
facsimile, so we might have TTY problems today!

73
Sheldon
WA4MZZ


jhaynes@alumni.uark.edu wrote:
> 
> Well I know this much.  They were used in Western Union's Plan 55 system
> for the USAF, late 1950s.  Which suggests they were probably standards for
> the U.S. military as a whole in that time period.  ZCZC has the property
> that the bit patterns are exactly the opposite for the two characters, so
> it is unlikely to be generated falsely.  In some of the switching
> equipment it is linefeed-NNNN that is detected as the end of message
> signal, so NNNN occurring just anywhere isn't taken as the end of message.
> 
> These signals are still used in military systems.  See ACP127(G) (which
> I found somewhere on the web, but I don't remember where.)
> 
> --
> 
> jhaynes at alumni dot uark dot edu
> 
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