The SDR-1000 uses a 200MHz reference clock, one selected for very low phase noise, a Valpey Fisher unit. The frequency stability on it is not so good (20ppm). New units use a temperature stabilizer around the clock generator to keep it from drifting so much. After a 5 minute warm up the frequency now stays dead on. That oscillator module is the most expensive item on the radio.
At 08:08 PM 6/10/2006, you wrote: >I agree that the DDS is not the best and I never said so, I was just >refering to the phase noise. >The spurs, aliases and digital artifacts are the problem and the newer >DDS from Analog are getting better and by using very high frequency >clock, 14 bit DACs and some other improvements minimize the spurs, in >particular when the output frequency is low. > >Regarding the phase noise: > > > *Phase noise at the output is that of the > > DDS clock source times the ratio of the > > output frequency to the clock frequency, > > as limited by divider noise. > >The output frequency is always lower than the clock frequency which >means that the phase noise will be reduced. The higher the clock >frequency the better. The problem is to obtain a good clock. >The SDR-100 uses a clock of only 125 MHz but that oscillator costs >something like $65.00 and cannot be bought in single unit. > >The newer DDS use 500 & 1000 MHz clocks and finding one is the problem. > >I am still looking for a good LO for my project. As it will be modular >I can start with a DDS-60 to see what performance I can get. For the 9 >MHz IF I will put the SoftRock Oscillator off board to play with >different oscillators, the phase noise of that oscillator must be >excellent but as it is a "low" fixed frequency it is easier to build. > >Jean-Claude PJ2BVU > > > > > > > >Yahoo! Groups Links > > > > Cecil Bayona KD5NWA www.qrpradio.com "Windows the worlds most successful software virus" ------------------------ Yahoo! Groups Sponsor --------------------~--> Get to your groups with one click. Know instantly when new email arrives http://us.click.yahoo.com/.7bhrC/MGxNAA/yQLSAA/ELTolB/TM --------------------------------------------------------------------~-> Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/soft_radio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
