Hi I believe the input clock on the DDS is 75 MHz. The data sheet for the DDS shows that as a correct input clock for the chip.
>From that the Nyquist is 37.5 MHz. The output of the DDS will go to 37 with a >crazy filter. That output forms the LO (or clock if you prefer) for the mixer. Bob On Jan 24, 2010, at 1:04 PM, Stephan Schaa wrote: > > Thanks for your explanations, Bob! > > I understand the principles of driving the mixer with a squarewave signal and > that you use a comparator to change sine to squarewave. > > Where I'm failing at is the trick how to receive 30 mhz with a DDS that make > 37 MHz max without getting problems with nyquist. Can you use a comparator to > double your VCO frequency without getting problems at the duty cycle? > > > Stephan > >
