You're right, it's for a USRP. I just got annoyed with the constant frequency offset, so I'm rolling my own. Turns out there isn't much available for good off-the-shelf 64MHz VCXOs. The USRP2 has built-in support for 10MHz sync, but not having one, I'm left to what I do have. Can't injection lock the oscillator on board, as it's a self-contained square-wave clock. So it looks like I'm going to try my hand at a Butler VCXO.
That said, I know that for PLLs, the maximum control loop bandwidth you can use is limited by the pullability of your oscillator: if you use a VCXO with very low Kv, you might end up with a maximum useful loop bandwidth of 10Hz. No sense in using a 10544A to tune that! The phase noise performance would be pretty awful, since you can't tightly lock the reference oscillator to it. So does it make more sense to use a high-Q LC oscillator instead, with a much higher Kv? I'd be able to phase-lock it much more tightly to the reference oscillator. Plus, a 64MHz LC oscillator is pretty easy to build. --n > Date: Tue, 9 Feb 2010 21:50:57 -0700 > From: [email protected] > To: [email protected] > Subject: Re: [time-nuts] Low phase noise VCO > > Hi Bob and all: > This is interesting, because I suspect this frequency source is for an > Ettus Research USRP. A little further downtimeline I will be faced with > this problem as well. The SDR is designed already and requires a 64 MHz > clock, especially as this clock is used for the microwave transmit and > receive front ends. I had planned a synthesizer filtered... > The oscillator that is in the USRP that I have is good only to about 1 > part in 10^8 or so for accuracy, better in stability. maybe the existing > osc. can be injection locked, or temp controlled in place. > Don > > Bob Camp > > Hi > > > > With most SDR's a spur on the clock creates a spur in the radio. No matter > > how you do your multiply, you will wind up with some sub-harmonics running > > around. Much better / easier / quicker to start at 64 or 65 MHz. > > > > Bob > > > > > > On Feb 9, 2010, at 8:32 PM, Bruce Griffiths wrote: > > > >> Thats not very useful when you want the 4th harmonic as its amplitude is > >> zero fro a 25% duty cycle. > >> Using a duty cycle of 1/8, 3/8 or 5/8 will maximise the amplitude of the > >> 4th harmonic. > >> > >> see: > >> http://www.wenzel.com/pdffiles1/pdfs/choose.pdf > >> > >> Bruce > >> > >> Max Robinson wrote: > >>> If you start with a square wave odd order is all you can get but if you > >>> start with a pulse with a 25% duty cycle you can get even order. It's > >>> best to optimize the pulse width for the harmonic you want. > >>> > >>> Regards. > >>> > >>> Max. K 4 O D S. > >>> > >>> Email: [email protected] > >>> > >>> Transistor site http://www.funwithtransistors.net > >>> Vacuum tube site: http://www.funwithtubes.net > >>> Music site: http://www.maxsmusicplace.com > >>> > >>> To subscribe to the fun with transistors group send an email to. > >>> [email protected] > >>> > >>> To subscribe to the fun with tubes group send an email to, > >>> [email protected] > >>> > >>> ----- Original Message ----- From: "Nick Foster" > >>> <[email protected]> > >>> To: <[email protected]> > >>> Sent: Tuesday, February 09, 2010 6:35 PM > >>> Subject: Re: [time-nuts] Low phase noise VCO > >>> > >>> > >>>> > >>>>> From: [email protected] > >>>>> To: [email protected] > >>>>> Date: Tue, 9 Feb 2010 18:24:39 -0600 > >>>>> Subject: Re: [time-nuts] Low phase noise VCO > >>>>> > >>>>> Which leads me to ask a novice question: > >>>>> > >>>>> Why not pull a 16 MHz crystal and multiply to 64 MHz? > >>>>> > >>>>> If you count down from 64 to 10 MHz, isn't the multiplication inside > >>>>> the > >>>>> PLL? > >>>>> > >>>>> Perhaps the noise is multiplied by 4, but would it work for the > >>>>> intended > >>>>> purpose? > >>>>> > >>>>> Bill Hawkins > >>>> > >>>> Can you do x4 multipliers? I thought odd-order harmonics were usually > >>>> used for multipliers. I'd be happy to be wrong! > >>>> > >>>> Nick > >>>> > >> > >> > >> > >> _______________________________________________ > >> time-nuts mailing list -- [email protected] > >> To unsubscribe, go to > >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> and follow the instructions there. > >> > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > -- > Dr. Don Latham AJ7LL > Six Mile Systems LLP > 17850 Six Mile Road > POB 134 > Huson, MT, 59846 > VOX 406-626-4304 > www.lightningforensics.com > www.sixmilesystems.com > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _________________________________________________________________ Hotmail: Free, trusted and rich email service. http://clk.atdmt.com/GBL/go/201469228/direct/01/ _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
