If I were doing it (and I might in the near future) I would use the DDS somewhere in mid range and heterodyne it up to the necessary 4X frequency.
Bob Macklin K5MYJ Seattle, Wa. "Real Radios Glow In The Dark" ----- Original Message ----- From: Bob Camp To: [email protected] Sent: Sunday, January 24, 2010 2:13 PM Subject: Re: AW: AW: AW: AW: [soft_radio] Re: LD-1 Discussion on Garage-shoppe.com Blog Hi A full wave rectifier can also be used as a simple broad band doubler. The problem with the output of the DDS is that without filtering it is far from symmetrical in the upper octave. Some use bandpass filtering to get around the problem, but that usually is not an option on a wide band radio. Bob On Jan 24, 2010, at 5:08 PM, Rotten Robbie wrote: 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 > > >
