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

Dana Whitlow k8yumdoober at gmail.com
Fri Jan 5 14:49:52 EST 2018


But what I'm wondering, because this is important to the discussion, is the
tone at a frequency encompassed on both sides by the noise band?  Or
is the tone outside the noise band?

Dana


On Fri, Jan 5, 2018 at 1:35 PM, Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> The audio (or RF) tone is summed with “baseband" noise. 1/F noise seems
> to be the flavor of the day in recent postings. The only reason to use
> audio
> in the example is that it is really easy to demonstrate things at audio
> with
> a sound card.
>
> Bob
>
> > On Jan 5, 2018, at 1:42 PM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> >
> > Is this an audio tone, summed with audio noise whose spectrum surrounds
> > that of the tone?
> >
> > Dana
> >
> >
> > On Fri, Jan 5, 2018 at 9:56 AM, Bob kb8tq <kb8tq at n1k.org> wrote:
> >
> >> Hi
> >>
> >> If I pass both a sine wave tone and a pile of audio noise through a
> >> perfectly
> >> linear circuit, I get no AM or PM noise sidebands on the signal. The
> only
> >> way
> >> they combine is if the circuit is non-linear. There are a lot of ways to
> >> model
> >> this non-linearity. The “old school” approach is with a polynomial
> >> function. That
> >> dates back at least into the 1930’s. The textbooks I used learning it in
> >> the 1970’s
> >> were written in the 1950’s. There are *many* decades of papers on this
> >> stuff.
> >>
> >> Simple answer is that some types of non-linearity transfer AM others
> >> transfer PM.
> >> Some transfer both. In some cases the spectrum of the modulation is
> >> preserved.
> >> In some cases the spectrum is re-shaped by the modulation process. As I
> >> recall
> >> we spend a semester going over the basics of what does what.
> >>
> >> These days, you have the wonders of non-linear circuit analysis. To the
> >> degree
> >> that your models are accurate and that the methods used work, I’m sure
> it
> >> will
> >> give you similar data compared to the “old school” stuff.
> >>
> >> Bob
> >>
> >>> On Jan 5, 2018, at 6:27 AM, Attila Kinali <attila at kinali.ch> wrote:
> >>>
> >>> On Tue, 2 Jan 2018 23:34:18 +0100
> >>> Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> >>>
> >>> [About AM noise being of equal power as PM noise]
> >>>
> >>>> Now, for actual sources this is no longer true. The AM noise can be
> much
> >>>> higher, which is why it can be a real danger to the PM noise if there
> is
> >>>> a AM to PM noise conversion. One source of such conversion can be the
> >>>> amplification stage, but another could be a mistuned filter, which
> have
> >>>> different amplitudes of the side-bands, which can create conversion as
> >>>> the balance does not balance the same way anymore.
> >>>
> >>> Yes, exactly. I am currently trying to understand how noise affects
> >>> circuits an how input and circuit noise get converted to output noise.
> >>> First assumption that needs to be dropped is that the noise processes
> >>> is purely additive and independent of the signal. This means that a
> >>> noise process does not anymore produce equal AM and PM power.
> >>>
> >>> I think I have a 90% solution of the noise processes and conversions
> >>> in a sine-to-square converter (aka zero-crossing detector, aka
> >> comparator).
> >>> But there is one process that keeps puzzling me. I think I know where
> in
> >>> the circuit it must come from, but I have no explanation as to how it
> >> happens.
> >>>
> >>>
> >>>                              Attila Kinali
> >>> --
> >>> It is upon moral qualities that a society is ultimately founded. All
> >>> the prosperity and technological sophistication in the world is of no
> >>> use without that foundation.
> >>>                -- Miss Matheson, The Diamond Age, Neil Stephenson
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