Does any limiter, soft or hard, [and perhaps any nonlinearity of power term 3 or greater in the amplifier of an oscillator] cause the "baseband 1/f noise to translate up to the resonator frequency [a form of crossmodulation]?. I wonder this because phase noise vs freq plots look a bit like the 1/f plots of a resistor, or active device, or power supply. Ceramic caps, and resonators [I`m thinking of quartz crystals] don`t pass much DC, and as I understand it, 1/f noise is associated with dc passing through resistors, or semiconductors. So the best way to go might be to have a very linear amplifier, which exhibits very low noise [perhaps 150dB below the operating level], with an AGC loop, that sets the operating levela little below the level at which the amp starts to clip - this could be done with a thermistor to avoid the AGC loop altering the [optimised] operating conditions of the amp. Alternatively you might be able to use a tetrode device like a dual gate MOSFET, and apply the AGC to the second gate. Thus you could keep the extremely linear amp extremely linear. [150dB below 1Volt RMS is 0.032uV RMS]. Cheers!........................................................................................................................................................................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 Sun, Jan 7, 2018 at 3:12 PM, Dana Whitlow <[email protected]> wrote: > One point about oscillator design I've not yet seen mentioned is this: the > limiter > must not degrade the resonator Q when in action. Hence, a pair of diodes > connected in parallel back to back, across a shunt resonator, would be a > bad > thing to do from the perspective of low phase noise. A differential > amplifier > that limits by running out of current on peaks, driving a shunt resonator, > is > a much better way even though one pays a price in having more transistor > noise in the circuit. > > I've long wondered if a very slow AGC might avoid the nonlinear mechanisms > issue except, of course, for things happening within the AGC loop's > bandwidth. > Is anybody reading this aware of what the truth really is? > > Dana > > > On Sat, Jan 6, 2018 at 4:29 PM, Magnus Danielson < > [email protected] > > wrote: > > > > > > > On 01/06/2018 10:31 PM, Joseph Gwinn wrote: > > >> ------------------------------ > > >> > > >> Message: 2 > > >> Date: Sat, 6 Jan 2018 09:19:31 -0500 > > >> From: Bob kb8tq <[email protected]> > > >> To: Discussion of precise time and frequency measurement > > >> <[email protected]> > > >> Subject: Re: [time-nuts] AM vs PM noise of signal sources > > >> Message-ID: <[email protected]> > > >> Content-Type: text/plain; charset=utf-8 > > >> > > >> 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. > > > > > > Hmm. Not strictly true. One can also use an AGC loop, like a wein > > > bridge oscillator. That said, some kind of softish limiter is commonly > > > used. > > > > Regardless what non-linear mechanism in play, this remains a non-linear > > mechanism that achieves the goal. Choose wisely. > > > > 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.
