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

[Jim Haynes]

On Mon, 2 Jul 2012, epvgk at limpoc.com wrote:
> 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.

I'm not familiar with the T.U. being discussed, but it takes a fairly 
small amount of logic to separate incoming and outgoing signals.  I sent
epvgk a schematic of such a circuit - if anyone else wants it just ask me.

Jim W6JVE