First of all, any osc multiplied up widens its sidebands (phase noise) by the multiplication factor and the inverse is also true. The DDS does a 20X to 200MHz and a divide by 20 to get back to 10MHz. I guess it's academic at this point how much jitter is added by the DDS until someone measures it.
Second, Rubidium standards are not intended to be used as local oscillators. They have terrible phase noise. They are intended to be used in timekeeping. It is their long term drift that excels, not short term phase noise. 73, k2ox -----Original Message----- From: John Ackermann N8UR [mailto:[EMAIL PROTECTED] Sent: Wednesday, January 04, 2006 3:16 PM To: Jim Lux Cc: [EMAIL PROTECTED]; [email protected] Subject: Re: [Flexradio] DIP OCXO for SDR Jim Lux wrote: > At 10:11 AM 1/4/2006, [EMAIL PROTECTED] wrote: > >>The SDR1000 can use clocks between 10MHz and 200MHz so long as when >>multiplied by an integer it equals 200 MHz. I use a 10MHz TCXO. >> >>73, >>k2ox > > > However, when you multiply up using the internal VCO, the phase noise takes > a hit. You might wind up with poorer noise (but more accurate frequency) > multiplying up from a 10 MHz TCXO. http://www.febo.com/geekworks/sdr1k/sdr1k_phase/index.html has screenshots that show the phase noise at the output of the DDS for the standard 200MHz oscillator, and an HP Rubidium frequency standard at 10MHz multiplied by 20 in the DDS. You can clearly see the phase-noise hit caused by the multiplication. John
