[time-nuts] AM vs PM noise of signal sources
joegwinn at comcast.net
Sat Jan 6 16:31:31 EST 2018
> Message: 2
> Date: Sat, 6 Jan 2018 09:19:31 -0500
> From: Bob kb8tq <kb8tq at n1k.org>
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] AM vs PM noise of signal sources
> Message-ID: <DDEF34DD-AD21-44C6-9612-D877881078E5 at n1k.org>
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> 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
> 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 ….
>> On Jan 6, 2018, at 1:53 AM, donald collie <donaldbcollie at 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
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