[MRCG] RTTY MK and SP Conventions

[willi6 at starpower.net]

Eugene, et al: 

Although I have seen TTY machines "beat themselves to death", my reference to the "resting between functions" was somewhat of a pun or perhaps double entendre.  It was also aimed at TTY, rather than the much earlier Morse inkers.  

The resting that I was thinking about was the need for the device to know when one character ended and the next character started.  Thus, in the earliest forms of teletype (versus Morse), the STOP Baud was a MK and slightly longer than the other "bauds" in the character.  The ST OP Baud ratio  was typically 1.42 based on the five character bauds being 1.0 and the STOP baud also being 1.0 baud.    This slight pause, allowed all the mechanical functions to come to a halt; e.g., clutches locked up, etc.  Then, the next character "announced itself" with a START Baud by going SP for 1.0 baud and the cycle repeated itself. 

Later on, when mechanical TTY ventured into ASCII, the Baud Rates moved away from the old Baudot standards (e.g., 1.42) and they started to rely on a 1.0 or 2.0 MK for the STOP, and the traditional 1.0 SP for the START. 

At the risk of starting another thread, there are those Baudot purists who can mathematically argue a good case that a 100 WPM mechanical Baudot machines was actually more efficient (if not technically faster)  than a 150 WPM mechanical ASCII machine.  8*) 

73,  Dave 

Dave Williams - K7HMP/4 
Stafford, Virginia 
  

----- Original Message -----

---------------------------------------------------------------------- 

Message: 1 
Date: Sun, 10 Aug 2014 09:40:20 -0700 
From: "W2HX" <w2hx at w2hx.com> 
To: "mrcg at mailman.qth.net" <mrcg at mailman.qth.net> 
Subject: Re: [MRCG] RTTY MK and SP Conventions 
Message-ID: 
        <ACBC68AC7928FA4FB768DFB3FDD641AC2DCDDCD15D at ex-be-032-sv1.shared.themessagecenter.com> 
         
Content-Type: text/plain; charset=utf-8 

The concept of marking and spacing derives from the early morse pen registers. A marking signal (current present) would cause the ink to mark on the strip of tape. Spacing would not move the pen and thus the tape would simply advance without any ink, creating a space on the tape. Nothing to do with equipment resting. Using the marks and space would represent the morse characters. Later baudot would use the the same concepts to indicate which of the 5 bits was present (mark) or absent (space) 

73 Eugene 


73 Eugene W2HX 

-----Original Message----- 
From: willi6 at starpower.net [willi6 at starpower.net] 
Received: Sunday, 10 Aug 2014, 12:20pm 
To: mrcg at mailman.qth.net [mrcg at mailman.qth.net] 
Subject: [MRCG] RTTY MK and SP Conventions 


The following is to some extent anecdotal as I can't find some of my books and paperwork to cite as formal references. 

In the good old days (60 Ma and DC Voltage and LL), the MARK was voltage and current present and space was line open.  This was to some extent because the mechanical contraptions needed to "rest" between functions, rather than to be "running open" and beating themselves to death. 

When TTY evolved to RTTY via Radio, the convention held, although sometimes the carrier shift and/or tone conventions varied. 

Where it first really started to go astray was when solid state conventions started to appear.  At the time, most digital "stuff" was Five Volts and Zero Volts (the zero was usually "floating" rather than the more purist "GROUND").  At some point, the EIA standard came along and the HIGH was -5 VDC and the LOW was +5 VDC (more or less).  (this was for signalling or communications, rather than internal to the devices, where the 5 VDC and 0 VDC was still prominant.)  Again, the LOW was more the digital assumption that a HIGH did not exist at that moment, so the signal must be a LOW by default. 

There were some portions of RS-232 that had the mark high (+) and the space low (-) but they were optional and not competing well in commercial circles against EIA. 

Enter the military.  For lots of different reasons (some practical and some traditional) the military leaned towards having the HIGH actually be "high" or Positive and the LOW actually be "low" or negative.  Likewise, for signalling purposes, they wanted to reclaim the ZERO as a GROUND and rather than either of the above. 

Eventually MIL-STD-188 in its many variations for signalling via neutral or balanced methodology pretty much won out in the military communications environments.    Generally speaking, in the Neutral portions of MIL-S TD-188, the Mark is +6 VDC and the Space is -6 VDC. 

Again, the carrier shift and/or tone pairs can vary depending upon specific systems. 

I suspect I may have over simplified some of this, especially how some of the spacing condit ions were handled when it was a floating digital Zero VDC.  On TTY gear, during this period (Late 60s and Early 70s), it was often necessary to "tie" the swinger arm on the KYBD and/or TD via a small resistor (10K?) to a Neg Six volts, to prevent the equipment from getting conf used.  Nothing is perfect. 

73,  Dave 

Dave Williams - K7HMP/4 
Stafford, Virginia 

----- Original Message -----