Mark Thorson > wrote:

>I built my own modem from an LM566 on the transmit side
>and an LM565 on the receive side and my own SerDes to
>interface to a TVT-II. Originally it was only 110 baud,
>because I was switching between two 566 oscillators,
>but I got it to 300 by switching components in the time
>constant of a single 566. By avoiding the discontinuity
>caused by switching between two unsynchronized oscillators,
>you can get much higher FSK baud rates.
>
>And yes, I built the triple power supply for the system from
>LM309, LM320, and LM340 series three-terminal regulators.

National seminconductor owes you a prize for this.

Steve