[time-nuts] AM vs PM noise of signal sources

jimlux jimlux at earthlink.net
Sun Jan 7 10:33:03 EST 2018

On 1/6/18 6:12 PM, Dana Whitlow 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.


That's the Wein bridge stabilized by a light bulb, popularized by Messrs 
Hewlett and Packard a while ago.

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