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 <donaldbcol...@gmail.com> 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 <mag...@rubidium.dyndns.org >>> wrote: >> >>> Joseph, >>> >>> On 01/05/2018 09:16 PM, Joseph Gwinn wrote: >>>> On Fri, 05 Jan 2018 12:00:01 -0500, time-nuts-requ...@febo.com 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 -- time-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >>> mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.