>>>>I've got a friend I'm helping out who wants to implement a 1200 Buad
>>>>MODEM in a PIC.
>>>>
>>>>Has anyone achieved this?  I think I have heard of people getting 300
>>>>Baud MODEMs to work.

>>hi i have a projekt that needs some knowledge about building small tranceivers
>like a miniature cordless phone (modemlink)
>
>

I built a 150 baud modem for a pic out of one IC, an LMC567. This little
chip is only 8 pins, and can detect a tone by simply pulling a  pin low when
the tone is detected. I'm not sure what its maximum throughput rate is, but
there are other chips (made by national semiconductor and others) similar to
this that should definately be able to go up to 1200 baud. I used an FSK
modulation system, using a 1N4002 diode in a crystal oscilator at 49.860 MHz
to shift the frequency between  two frequencies, one for mark, the other for
space. The diode was driven by a transistor which in turn was driven by a
PIC pin. The diode acted as a varactor, i.e. its capacitance in the reversed
biased state depended upon the reverse bias voltage, which was switched
between two levels by the transistor. On the receiver end, there was a
direct conversion receiver consisting of an RF preamp, an NE602
mixer/oscilator, and a single transistor audio amp, the output of which went
directly to the LMC567, which then switched hi/low a pin on the PIC. When I
got at least a 70mv audio signal out of the audio amp of the receiver, the
system worked very well.
The system was for a keyless entry system.

Good Luck,
Sean