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

[Nick England]

No, nothing in the M28. The TU figures that anything (other than
itself) that breaks the loop is transmitting - so a keyboard and/or TD
in the loop would activate the TU's PTT line.

Here's an overview of Navy TU units
http://www.navy-radio.com/rtty-tu.htm

And if anyone is interested, a detailed description and schematic of
the tube/relay logic of the commonly used AN/SGC-1A TU is at
http://www.navy-radio.com/rtty/sgc1/sgc1a-op.pdf

cheers,
Nick K4NYW
www.navy-radio.com


On Mon, Jul 2, 2012 at 1:19 PM,  <epvgk at limpoc.com> wrote:
> 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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