For this application Nyquist does not matter. It is just used as a clock.And what you need for the detector is a square(rectangular) waveform.
If the waveform is reasonably symetrical you can use both edges for frequency doubling. It just takes a few inverters for a time delay and an exclusive OR. Bob Macklin K5MYJ Seattle, Wa. "Real Radios Glow In The Dark" ----- Original Message ----- From: "Dave Wade" <[email protected]> To: <[email protected]> Sent: Sunday, January 24, 2010 1:56 PM Subject: Re: AW: AW: AW: AW: [soft_radio] Re: LD-1 Discussion on Garage-shoppe.com Blog > > > k5nwa wrote: >> At 12:04 PM 1/24/2010, you 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 >>> >> >> This is a mixer, you are not trying to digitize the 30MHz signal >> where you would need a minimum of two samples, instead you are mixing >> it down to the base band. > > No but the DDS chip is synthesising a sine wave from samples, and > Nyquist bite both ways. However some DDS chips (I don't know about this > one have on-board frequency multipliers... > > >> >> >> Cecil >> k5nwa >> www.softrockradio.org www.qrpradio.com >> < http://parts.softrockradio.org/ > >> >> Never take life seriously. Nobody gets out alive anyway. >> >> >> >> ------------------------------------ >> >> Yahoo! Groups Links >> >> >> >> > > > ------------------------------------ > > Yahoo! Groups Links > > >
