[GreenKeys] M28 half vs full duplex? One loop or two?

[epvgk at limpoc.com]

On Mon, Jul 02, 2012 at 11:17:44AM -0400, Nick England wrote:
> Here's my understanding of how the Navy did it -
> 
> TT-176B's were wired with keyboard and printer in the same loop so you
> could see what you were typing and have a complete printed record of
> the communication.
> They were interfaced to two types of systems, TONE or CFS -
> The TONE TU (mainly for UHF transceivers) would switch into transmit
> automatically when you typed. The CFS system (HF) had separate rcv
> converter and xmt keyer - you manually used an external rcv-xmt
> switch. Shipboard, a C-1004/SG control box would have been associated
> with the TT-176
> http://www.navy-radio.com/rtty/c1004.htm
> 
> Hams usually had/have TU boxes hooked to a transceiver and run the
> equivalent of TONE operation.
> 
> cheers,
> Nick K4NYW
> www.navy-radio.com

How did the terminal unit "know" to switch to transmit, and back? If the kbd
and typing unit were in series, how would it know you've started typing rather
than just received a character on the loop from somewhere else? Is there a
modification to the M28 that signals that? If so, it'd be nice to have an
alternative to a manual transmit/receive switch. 

eric


> 
> On Mon, Jul 2, 2012 at 10:59 AM, Chris Elmquist <chrise at pobox.com> wrote:
> > I'm getting close to having my M28 "skintight" TT-176B up and running
> > and was working on it this past weekend.
> >
> > I'm not sure if this unit is the "tempest" version but it does have a
> > line filter assembly through which both the AC line and the loop feed
> > into the unit at the back of the LESU.
> >
> > What's a little puzzling to me is that there is just one circuit through
> > the filter for the loop.  It enforces that the keyboard and the printer
> > must be in series and then there is just a single + and - loop connection
> > coming away from the unit.  This means that it will be half duplex--
> > it will print what is locally typed.  At least, I think that's the idea.
> >
> > Was this the normal configuration of this unit?  or was it also configured
> > with the keyboard and the printer on separate loops?  So that you could
> > have a full duplex connection?
> >
> > I kind of live in a cross-over space between TTYs used for wireline and
> > radio comms and those hooked to computers.  My Altair 680b has a monitor
> > PROM that can support a 5-level baudot TTY as the console.  But there,
> > the keyboard loop and the printer loop are separate-- very similar
> > to how it was often done with ASCII M33 machines.   So, I'm a little
> > confused/curious about the "normal" way of using a 5-level machine and
> > it's loop (or loops)...
> >
> > Chris
> >
> > --
> > Chris Elmquist
> >
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