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

[donald collie]

I`m looking at the circuit of an H/P10544 oscillator - can anybody confirm,
please, if the H'P transistor types : 53-20, and 54-215 have commercial
equivalents?
Thankyou....................................................
............................................................
............................................................
...............................................Don.

On Mon, Jan 8, 2018 at 1:02 AM, donald collie <donaldbcollie at gmail.com>
wrote:

> 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
>
>
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> On Sun, Jan 7, 2018 at 3:12 PM, Dana Whitlow <k8yumdoober at gmail.com>
> 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 <
>> magnus at 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 <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>
>> > >> 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
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