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

donald collie donaldbcollie at gmail.com
Sun Jan 7 23:53:47 EST 2018

 Wien bridge and bridged T oscillators often use a thermistor  [lamp] to
set the  amplitude below saturation, for low distortion, but i`ve seen the
diode AGC method used.
Conversely, you could use a thermistor to set the output of a crystal or
L/C oscillator. One other method seems to be to let the oscillator limit
somehow, and then rely on the filtering action of the resonator to purify
the output. Is this shutting the barn door, after the horse has egreased,
though - especially with close in phase noise, which doesn`t get filtered
as much?. One possible advantage of the thermistor approach would be that
the gain can be reduced without changing the active device`s operating
point, which may have been chosen after conciddering  number of factors :
Oscillator amplitude, best phase noise , linearity. etc. Thankyou Jeff for
pointing out that for best results, maximum output is not always sought.
Looking at my H'P 10544A circuit I see a slow, diode AGC, and a single
2N4125 [?] oscillator transistor with AGC applied to its emitter. I guess
that the voltage gain through the crystal means that the oscillator
produces the expected output with this transistor loafing along, causing
the PM mechanism[s] in this transistor not to be as large as they might
well be if the oscillator was limiting.
Cheers!...............................................................Don C.
P.S.: I`m not learned, just enthusiastic ;-)

On Mon, Jan 8, 2018 at 3:08 PM, Gerhard Hoffmann <dk4xp at arcor.de> wrote:

> Am 07.01.2018 um 17:05 schrieb Arnold Tibus:
>> but I see quite often mentioned the 'Wein bridge'. (Wein in german is
>> 'vino' or 'wine' ;-)
>> Not of real technical importance, but shouldn't this not be correctly
>> called a 'Wien bridge'?
>> As I know that this tricky circuit was developed by Max Wien in 1891.
>> Max Karl Werner Wien was a German physicist and the director of the
>> Institute of Physics at the University of Jena at that time.
>>  (sorry, I am a nut ;-)  )
> He shares that fate with a certain Mr. Seimens and the famous Oscar Meyer
> Weiner.
> That must be a German->American sound shift, some kind of extension to
> Grimm's law.
> There also was a Mr. Hamming, but there never was a Mr. Hanning, at least
> not
> in the business of weighting contents of time series.
> That guy with the window function was one Mr. Julius von Hann, an
> Austrian Meteorologist. It is therefore the Hann window.
> <    https://en.wikipedia.org/wiki/Julius_von_Hann    >
> cheers, Gerhard
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