Hi ….. except you can decide to use a “25%” design for your oscillator or you can go with a “50%” kind of circuit. It’s going to be a bit tough finding a crystal that is 2X higher Q …. Rick’s papers go through a bit of just *why* you would go with the “25%” circuit.
Bob > On Jan 6, 2018, at 9:25 AM, Magnus Danielson <[email protected]> > wrote: > > Hi, > > I think loaded Q is being used as term these days for the effective Q of > the resonator as loaded by the support amplifier. > > The Leeson model only models how noise types gets created, not how a > physical design actually works. > > The modified Leeson model starts to approach the actual design. > > Cheers, > Magnus > > On 01/06/2018 03:19 PM, Bob kb8tq wrote: >> Hi >> >> The key point missing is the fact that any real oscillator must have a >> limiter >> in the loop. Otherwise it will “create one” by going over the max output of >> this or >> that amplifier. To the degree that the limiter has issues (limits poorly) >> you will get >> AM noise. >> >> On a practical basis, loop Q is as significant as resonator Q . The various >> elements in the loop degrade the total Q by a significant amount. Getting 25 >> to >> 50% of the resonator Q is “doing well” with his or that common circuit. Yes, >> there >> are even more layers past this …. >> >> Bob >> >>> On Jan 6, 2018, at 1:53 AM, donald collie <[email protected]> wrote: >>> >>> So to be lowest noise, an oscillator should have the highest Q resonator >>> possible in its feedback loop, operate in class "A" [for maximum >>> linearity], and utilise active amplifier device(s) that contribute the >>> least noise [both amplitude, or 1/f], and phase. This latter implies >>> operating the active device at maximum output level [ie signal to noise]. >>> The quality of the power supply effects the amplifier SNR, so in the >>> persuit of superlative oscillator phase noise, the power supply should be >>> as good as possible. >>> Resistors in the oscillator carrying DC make 1/f noise - the best in this >>> respect are the metal type, I think - so use metal resistors or WW. >>> What are the other conciderations that come into the design, for lowest >>> noise of the oscillator itself >>> Split, then >>> lump...;-).................................................Cheers, de : Don >>> ZL4GX >>> >>> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> >>> Virus-free. >>> www.avg.com >>> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> >>> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> >>> >>> On Sat, Jan 6, 2018 at 1:08 PM, Magnus Danielson <[email protected] >>>> wrote: >>> >>>> Joseph, >>>> >>>> On 01/05/2018 09:16 PM, Joseph Gwinn wrote: >>>>> On Fri, 05 Jan 2018 12:00:01 -0500, [email protected] wrote: >>>>>> Send time-nuts mailing list submissions to >>>> >>>>>> If I pass both a sine wave tone and a pile of audio noise through a >>>>>> perfectly >>>>>> linear circuit, I get no AM or PM noise sidebands on the signal. The >>>>>> only way >>>>>> they combine is if the circuit is non-linear. There are a lot of ways >>>>>> to model >>>>>> this non-linearity. The “old school” approach is with a polynomial >>>>>> function. That >>>>>> dates back at least into the 1930’s. The textbooks I used learning it >>>>>> in the 1970’s >>>>>> were written in the 1950’s. There are *many* decades of papers on >>>>>> this stuff. >>>>>> >>>>>> Simple answer is that some types of non-linearity transfer AM others >>>>>> transfer PM. >>>>>> Some transfer both. In some cases the spectrum of the modulation is >>>>>> preserved. >>>>>> In some cases the spectrum is re-shaped by the modulation process. As >>>>>> I recall >>>>>> we spend a semester going over the basics of what does what. >>>>>> >>>>>> These days, you have the wonders of non-linear circuit analysis. To >>>>>> the degree >>>>>> that your models are accurate and that the methods used work, I’m >>>>>> sure it will >>>>>> give you similar data compared to the “old school” stuff. >>>>> >>>>> All the points about the need for linearity are correct. The best >>>>> point of access to the math of phase noise (both AM and PM) is >>>>> modulation theory - phase noise is low-index modulation of the RF >>>>> carrier signal. Given the very low modulation index, only the first >>>>> term of the approximating Bessel series is significant. The difference >>>>> between AM and PM is the relative phasing of the modulation sidebands. >>>>> Additive npose has no such phase relationship. >>>> >>>> May I just follow up on the assumption there. The Bessel series is the >>>> theoretical for what goes on in PM and also helps to explain one >>>> particular error I have seen. For one oscillator with particular bad >>>> noise, a commercial instruments gave positive PM nummbers. Rather than >>>> measuring the power of the signal, it measured the power of the carrier. >>>> Under the assumption of low index modulation the Bessel for the carrier >>>> is very close to 1, so it is fairly safe assumption. However, for higher >>>> index the carrier suppresses, and that matches that the Bessel becomes >>>> lower. That's what happen, so a read-out of the carrier is no longer >>>> representing the power of the signal. >>>> >>>> However, if you do have low index modulation, you can assume the center >>>> carrier to be as close to full power as you want, and the two >>>> side-carriers has a very simple linear approximation. >>>> >>>> Cheers, >>>> Magnus >>>> _______________________________________________ >>>> 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. >> >> _______________________________________________ >> 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. _______________________________________________ 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.
