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 <mag...@rubidium.dyndns.org > 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 <kb...@n1k.org> > >> To: Discussion of precise time and frequency measurement > >> <time-nuts@febo.com> > >> Subject: Re: [time-nuts] AM vs PM noise of signal sources > >> Message-ID: <ddef34dd-ad21-44c6-9612-d87788107...@n1k.org> > >> 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 -- 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.
