[time-nuts] Low phase noise VCO

Bob Camp lists at cq.nu
Wed Feb 10 00:40:31 UTC 2010


Would 65 MHz work as well as 64? It certainly would be easier to come up with.


On Feb 9, 2010, at 6:41 PM, Nick Foster wrote:

> Gentlemen,
> Not being an oscillator guru, I thought I'd ask here. I'm building up a fixed-frequency 64MHz PLL oscillator which uses a 10MHz reference. The reference is a homebrew HP 10544A-based GPSDO which seems to work OK. I've built a phase comparator based on a CoolRunner-II CPLD which implements a flip-flop phase-frequency comparator just like the CMOS 4046. Seems to work great, although I haven't put it to the test yet with respect to phase noise. So all I need now is the VCO.
> Right now, all I need is 64MHz to clock a software-defined radio, so I was thinking about using a VCXO. I see lots of solutions using LC oscillators, but very few using crystals because overtone crystals can't be pulled very far at all. So my question is, what type of oscillator would you recommend for this project, an overtone crystal oscillator like a Butler, or an LC oscillator? Is there a particular oscillator topology you favor, or (better yet) a schematic of one you like?
> Thanks,
> Nick
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