[GreenKeys] ZCZC and NNNN

Mon, 1 Dec 2003 17:02:03 -0500

FAA used ZCZC as part of the 'conditioning' at the beginning of traffic.
AFTN (an ICAO aviation net) also used this.  The ZCZC opened up a circuit,
and further coding (KMIAYFYF for instance) opened either a punch or printer
to receive traffic, and the NNNN deselected it.  Why the choice of ZCZC?  I
dunno.  It's already been pointed out that Z and C alternate bits like RY
does.  Just to limber up the machines??

Our end of message was LTRS CR CR (10) LF NNNN
This advanced the paper so the traffic could be torn off immediately for
distribution..  We used 2 part ncr paper for a record copy which rolled up
on a paper winder.  We saved for the traffic for15 days and discarded it..

It's been a while, so I can't remember what was explained to us as to the
why.

Gil, W1RG
----- Original Message ----- 
From: "Sheldon Daitch" <[email protected]>
To: <[email protected]>
Sent: Monday, December 01, 2003 4:10 PM
Subject: Re: [GreenKeys] ZCZC and NNNN

> 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
>
>
> [email protected] 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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