[GreenKeys] Phone connection for telegraphing

[Bob McConnell]

KD7JYK DM09 wrote:
> Speaking of such things...
> 
> Many years ago, a lot of Hams used to sent out ASCII text messages and
> beacons using Bell 103 modems.
> 
> Once a modem hasd linked up with another one, it's simple enough to send a
> text file, but how did these fellows just hit send and have it spew out the
> phone jack and over the radio with no handshaking or anything?
> 
> How did the fellow on the other end receive the signals and dump the audio
> into the pphone jack on his end and have text show up on the screen?
> 
> What is the trick to get modems to send and receive blindly in simplex
> mode???

Most of the early modems, Bell 103, 202 and 212 models, were dumb modems 
and had jumpers or switches to set the options. This was before Hayes 
defined the AT command set and put a CPU in the modem. So one end would 
have the originate switch set, while the other had answer. The phone had 
to be dialed manually and the hook switch pulled up to a third position 
to switch the modem into the circuit. So it was pretty easy to connect 
them up without even having dial tone or ringer signals. Some modems 
didn't even need a battery connected across the line to power the phones.

You can simulate this with smart modems with a matched set of commands 
at each end. I used to use Hayes modems to set up a circuit on dry 
copper pairs. I think it was ATO for originate and ATA to answer. Then 
ATH would disconnect.

Bob McConnell
N2SPP