[GreenKeys] TD operation on 28ASR

[Nick England]

I’ve been so deep inside these things that I forget not everyone else is.

Here’s a summary of the 28ASR:
The TD transmitter and the keyboard transmitter are always wired in series
in the signal loop. If the TD clutch is energized both can operate. So for
instance you can type a message header, read a tape with the message, type
in some more, etc.
1- in K mode, the keyboard transmitter is active but the TD is not
energized (hence my puzzlement). No tape is punched.
2- in KT mode, both the keyboard and TD are active, and tape is
simultaneously punched from the keyboard (but not from the TD - the punch
is mechanically connected to the keyboard)
3- in T mode, the keyboard does not transmit but it does punch tape. The
keyboard/punch speed is higher in this mode so you can punch tape as fast
as you can type. The TD can transmit while you are doing this.

I’ve looked at a number of Bell and Navy schematics and all show the TD
inactive in K mode.

T mode makes sense to me for a QSO only if you are a really good/quick
thinker and typist. While the other side is transmitting, you could be
cutting a tape with your response, then play the tape when it is your turn.
I’m not that good/quick.

K mode makes sense to me if you don’t ever want to run a “brag tape” or
other set message.

KT mode only makes sense if you want to punch a record of what you type.

All this is no big deal, I am just attempting to understand the rationale
and assumptions about actual operating procedure.

Note: the “normal” 28ASR has a tape perf which is only mechanically
operated by the keyboard. If a reperf is installed, it is still
mechanically operated by the keyboard - or by a completely different loop
than the one the keyboard, TD, and printer are connected to. Likewise if an
auxiliary (dome) reperf is installed, it is completely electrically and
mechanically separate from the rest of the ASR. It has its own motor and
gears.

I came late to teletypery so am generally ignorant about how things were
actually used, hence my curiosity.

Thanks for all the comments.
Nick


On Sun, Feb 9, 2020 at 7:17 PM Nick England <navy.radio at gmail.com> wrote:

> Looking at schematics in preparation for my rewiring job, I was surprised
> to see that the TD clutch can not be activated in K mode, only in KT and T.
> Why is that? It makes sense to me that normal conversation would take
> place in K mode with no need to perf a tape. But you might like to run a
> tape through the TD without having to switch from K to KT.
> What do you think? What am I missing?
> Cheers
> Nick
>
> --
> Nick England K4NYW
> www.navy-radio.com
>
-- 
Nick England K4NYW
www.navy-radio.com
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