[MRCG] RTTY MK and SP Conventions

[willi6 at starpower.net]

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 -----

From: mrcg-request at mailman.qth.net 
To: mrcg at mailman.qth.net 
Sent: Sunday, July 27, 2014 2:30:42 PM 
Subject: MRCG Digest, Vol 26, Issue 8 

Today's Topics: 

   1. Re: RTTY net (Steve) 
   2. Re: RTTY net (Ray Poularas) 
   3. Re: RTTY net (Jason W6IEE) 
   4. Re: RTTY net (Mark J. Blair) 
   5. Re: RTTY net (Tim) 
   6. Re: RTTY net (Mark J. Blair) 


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

Message: 1 
Date: Mon, 21 Jul 2014 18:08:36 -0700 
From: "Steve" <zarco at sonic.net> 
To: "West Coast Military Radio Collectors Group" 
        <mrcg at mailman.qth.net> 
Subject: Re: [MRCG] RTTY net 
Message-ID: <000f01cfa549$79ec2af0$276194d1 at starwars> 
Content-Type: text/plain; format=flowed; charset="iso-8859-1"; 
        reply-type=response 

It'll be a while till I'm setup to transmit but can receive any 
shift now. Very happy to copy and give signal reports. 
Have model 15's and 28's up and running currently. A MITE 
and TT-4 waiting in the wings. 
                               Steve W6SSP 
----- Original Message ----- 
From: <boatanchor at martasystems.com> 
To: "West Coast Military Radio Collectors Group" <mrcg at mailman.qth.net> 
Sent: Monday, July 21, 2014 1:17 PM 
Subject: Re: [MRCG] RTTY net 


> Jim, Steve - 
> 
> I just reconnected my GRC-42 (minus shelter) and tested it last weekend, 
> so I'm ready to try, but I'm not available until after Aug 4th. 
> 
> I think WB6AS Scott is about ready with his GRC-19 + Mite. Don't know if 
> Mark NF6X is ready, but we talked about trying maybe on a Sunday evening - 
> does that work ? 
> 
> BTW, for me it'll have to be 850hz shift 45.5 baud baudot. I think old 
> clatternet ran Mark=Low, but I can run either way. ( Remember LSMFT from 
> the Lucky Strike ads? An old timer TTYer told me: LSMFT = lower space 
> makes fine teletype ) 
> 
> How about a readiness check-in on this list for anyone interested ? Come 
> now... 
> 
> John WB6AZP 
> 
> 
> 
> 
> 
> -----Original Message-----