1964 Antique MODEM Live Demo

[Chris Elmquist]

On Thursday (05/28/2009 at 04:03PM -0700), Brent Hilpert wrote:
> 
> (pedantic: His technical description was a little off, it's FSK, not an
> 'interrupted' tone.)

Agreed.  He started to get on track but then fell off again when he started
saying the tones were a function of the voltage level coming in on the
RS232 port and that because his laptop had too low of a voltage on that
port, he was getting the wrong tones.  This whole discussion in the context
of the modem being analog-- implying that he was getting tones that were
off frequency due to the incorrect voltage level.  I don't think it went
quite like that.

> Does anyone know if the frequencies for the 110 and 300 baud modem standards
> were the same or different?

They were the same.  Bell 103 tones...

http://en.wikipedia.org/wiki/Bell_103

I have several early Multi-Tech acoustic couplers here...  FM300 which
was indeed analog--  done entirely with opamps as active filters and
then FM30 which was Multi-Tech's first digital discriminator design.
I spent a fair number of my formative years working at Multi-Tech.  I was
there when the FCC ruling changed allowing customer owned equipment to
connect directly to the phone line.  That was a big day... and almost
instantly spelled the end of acoustic couplers :-)

Chris

-- 
Chris Elmquist