Wednesday, October 25, 2006
A SDR based on some K2 design ideas
Here is a diagram of a SDR that uses ideas from the K2 RF front end and PLL synthesizer:
It would use the K2's RF front end. I would substitute the TUF-1 mixer of the K2 with a switching mixer based on a FST3125 bus switch. The QSD would be at a fixed IF of 5 MHz. The LO for the QSD would be derived from a fixed 20 MHz oscillator divided by 4 to generate the quadrature signals needed to driver the QSD switches. The K2's PLL would be modified by eliminating the variable reference oscillator (resulting in the PLL tuning in 5 kHz steps) and substituting one of the LMX National PLLs for the MC145170 PLL used in the K2 design. The K2's VCO design is good, but I would also eliminate the VCO AGC circuit of the K2.