1964 Antique MODEM Live Demo

[Eric Smith]

Gordon JC Pearce wrote:
> Okay, let's try again.  I have a circa-70s 300-baud modem, that will
> generate incorrect tones when it's plugged into a USB-to-serial
> converter, but not when it's plugged into a real serial port.
>
> Why might this happen?
>
>   
The USB-serial adapter may be driving some of the other EIA-232 
(formerly RS-232) signals differently than the "real serial port", and 
that might change the behavior of the modem, for instance by switching 
it from originate to answer mode, or switching it to V.21 frequencies 
for non-US operation, or putting it in analog loopback mode for testing, 
or...

By the way, a 103 or V.21 modem doesn't actually have a fixed baud 
rate.  They were officially specified for operation up to a maximum of 
300 baud, but some people were able to get the 103 to work at 450 baud.

Eric