29 May
2009
29 May
'09
5:34 a.m.
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