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:

K2LikeSDR.pdf

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.

2 comments:

Anonymous said...

The K2 is a good choice for experimenting. It is e.g. very well possible to couple two K2 frontends and make them phase coherent. Using the SSB-filter module I/Q processing is not needed. See: http://www.pa0sim.nl/Hardware.htm
All the processing is done in the software.

73 Jan PA0SIM

Gian I7SWX said...

Hi Phil,

I do agree 100% with you on the K2 SDR idea. The 2T H-Mode Mixer with FST3125 has been already applied as a mod to replace the TUF1 mixer giving a very high IP3 improvement. Having a strong front end conversion followed by the classic QSD with FST3125 will certainly be appreciated by HF people and give a distance to many commercial receivers.
Although the TUF replacement with the H-Mode Mixer is a 1 to 1 job, I can deliver all info on this mode.

73

Gian
I7SWX
I can del