Hi Bruce, Thanks for explaining - the picture is starting to become clearer. I knew there must be a reason why commercial multipliers are so expensive.
If I understand you correctly the variation in phase (or group delay) caused by a variation in temperature messes with the Allan deviation. I can see that a high Q filter will probably have a quite sensitive temperature/phase dependency. I guess that crystal filters will also have a large temperature/phase dependency. The other side of the coin is that unfiltered harmonics ruins the phase noise. I now also understand the merit of Rick's suggestion - it avoids odd-order multiplication all together. Thanks for the doubler circuit you posted - it seems quite nifty. Maybe my best option (from a design time/cost point of view) is to double to 20MHz and then buy the commercial x5 to get a 100MHz? Regards, Stephan. > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > Behalf Of Dr Bruce Griffiths > Sent: 01 March 2007 03:52 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Low noise frequency multiplication > > Stephan Sandenbergh wrote: > > Hi Rick, > > > > You are absolutely right - I should've mentioned the specs first. > > > > It is an Oscilloqaurtz 8788 locked to GPS. > > > > Phase noise at 10MHz: > > Hz dBc/Hz > > 1 -100 > > 10 -130 > > 100 -152 > > 1e3 -160 > > 1e4 -165 > > 1e5 -165 > > 1e6 -165 > > > > Allan dev: < 1.10e-12 (not locked) > > > > I suspect that it shouldn't be too hard to preserve these specs. (that > is > > apart from the obvious 20dBc/Hz increase due to the 10x multiplication). > > > > Noise floor is of importance since I'm clocking ADCs and DDSs. These are > > affected by high frequency jitter. I've got more than one of these > > crystals/ADCs/DDSs which I would like to keep reasonably synced (the > reason > > for the common-view GPS) so the longer time scales are also important. > > > > I just noted that the noise level of that diode multiplier in the > previously > > mentioned article is way below that of my OCXO. From there my curiosity. > > > > I agree that phase-locking to 100MHz oscillator is the best way to go, > but > > as a first iteration multiplication is a good start. > > > > Judging by your reply the x2 and x5 approach should probably be avoided? > > > > Regards, > > > > Stephan. > > > > > > > >> -----Original Message----- > >> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > >> Behalf Of Rick Karlquist > >> Sent: 01 March 2007 01:42 AM > >> To: Discussion of precise time and frequency measurement > >> Cc: 'Discussion of precise time and frequency measurement' > >> Subject: Re: [time-nuts] Low noise frequency multiplication > >> > >> Stephan Sandenbergh wrote: > >> > >>> How difficult is it to multiply a frequency standard from 10MHz to > >>> > >> 100MHz? > >> > >>> The other day I stumbled across the following article on Wenzel's > >>> > >> website: > >> > >>> http://www.wenzel.com/pdffiles/RFDesign2.pdf > >>> > >>> > >>> > >>> It describes a way in which an analogue odd-order frequency multiplier > >>> could > >>> be built cheaply with superior noise characteristics. This circuit > that > >>> > >> is > >> > >>> described is really simple and quite ingenious. Unfortunately, I would > >>> like > >>> > >> I remember that article from when it was first published. It is > >> quite clever, but has no special phase noise advantage compared > >> to any other passive limiter or passive frequency doubler based > >> on a full wave rectifier. > >> > >> You need to be more specific about your multiplier requirements. > >> When I worked for Zeta Labs, we used to get vague RFQ's like this for > >> multipliers, and then have to develop a specification. That is > >> almost more difficult that actually building the multiplier. > >> Are you after good Allan deviation or low phase noise? Do you > >> care about phase noise floor? How clean is the original oscillator? > >> In the HP 8662, they double a 10811 three times to 80 MHz and then > >> strip off the phase noise floor sidebands with a crystal filter. > >> > >> Regarding X10: I suggest you double to 20 MHz, take that as an > >> intermediate output, and then quadruple the 20 MHz to 80 MHz. > >> Then mix the 80 and 20 to get 100 MHz. As far as heroically > >> multiplying directly by 5: been there, done that, got the coffee > >> mug and T-shirt. Don't do this at home kids. > >> > >> Rick Karlquist N6RK > >> > >> > >> _______________________________________________ > >> time-nuts mailing list > >> [email protected] > >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> > > > > > > _______________________________________________ > > time-nuts mailing list > > [email protected] > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > > > Stephan > > The problem is essentially the difficulty in filtering out all the > unwanted harmonics. > Using a high Q bandpass filter will increase the phase instability due > to temperature variations and drift. > Even reactive components contribute phase noise which is exacerbated in > a high Q tuned circuit. > > It is better from the phase noise perspective to use notch filters to > attenuate the unwanted harmonics and subharmonics rather than a high Q > bandpass filter tuned to the desired frequency. > > The filtering problem is made worse by the fact that the unwanted lower > harmonics all have larger amplitudes than the desired 5th harmonic. > > Multiplying by 2 in a balanced circuit ensures that the fundamental > content of the output is suppressed by 20dB or more with respect to the > second harmonic and all higher harmonics have significantly lower > amplitudes than the 2nd. A balanced circuit also suppresses the odd > harmonics. > > As far as low phase noise dividers are concerned conjugate regenerative > dividers can have significantly lower noise than digital dividers. > However these dividers are quite complex as they use a mixer plus at > least one amplifier a phase shifter or two and a pair of bandpass > filters. Adjusting them for low noise operation isn't easy. > > Bruce > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
