AW: Ring mod circut...

[Haible Juergen]

If you want to go really cheap, use the 1496 chip.
(see my Frequency shifter page for circuit details, or
the 1496 data sheet ...)

If you want to go precision and still affordable, try the RC4200.
I think Ric Miller has the circuit (from Barry Klein) on his page.
I have built it (with carefully selected resistors), and it works 
excellent. (But you should match the impedance of the offset
trim inputs to the impedance of the normal inputs for the last
bit of temperature stability.)

JH.