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Reply-To: "Fred Bartoli"
From: "Fred Bartoli"
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Subject: Re: Aylward, Engelhardt: Noise in a transient sim?
Date: Sat, 26 Oct 2002 22:47:54 +0200
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NNTP-Posting-Date: 26 Oct 2002 22:47:25 MEST
"John Woodgate" a écrit dans le message
> I read in sci.electronics.design that Kevin Aylward
> wrote (in r.ntli.net>) about 'Aylward, Engelhardt: Noise in a transient sim?', on
> Sat, 26 Oct 2002:
> >I disagree that I have been talking past the dude.
> Well, he clearly doesn't understand you, and I don't think you
> understand him too well.
> You are just standing too close to the argument to see what is
> happening. I've no doubt that if you could understand each other, you
> would agree. So I tried posting something you MAY be able to agree on.
> Regards, John Woodgate, OOO - Own Opinions Only.
> Interested in professional sound reinforcement and distribution? Then go
> PLEASE do NOT copy news posts to me by E-MAIL!
I quite agree with you John. I just think that they're just not speaking
about the same thing.
So here's my attempt :
Suppose a 100MHz waveform that have harmonic contents up to the now famous
7GHz and that the waveform is time invariant (repetitive).
Its spectrum is *only* made of *discrete* n*100MHz frequencies and
absolutely nothing else. So it's BW is absolutely 0.
Another way of seeing that is that it can be transmitted without loss
through a bank of bandpass filters centered on n*100MHz of arbitrary small
That's what Mike fails to grasp.
It doesn't mean at all that this can be transmitted through a 0BW amplifier,
in the common sense we see them as 0BW *lowpass* or *bandpass* (with only
Mike's "arbitrary" signal is not arbitrary at all. It's an *arbitrary
choosen* waveform which is indefinitely repeated. There's no randomness
here, except when one choose the waveform at the beginning. And again it has
zero bandwidth in the sense it occupies only *discrete* frequencies in the
spectrum, whatever the number of harmonics.
As soon as the waveform change *over time* the bandwith increase from 0 to
some finite value.
If the bandwidth is too large (the waveform change too fast) Mike's sampler
will fail to follow the change.
Another way of seeing that is that a sampler is a mixer. The binary sampler
mixes *all* the harmonics of the signal down to DC, and the allowed
bandwidth is that of the loop low pass filter and it's all its interest
since that allow noise reduction. Seeing that make us understand that
there's almost no difference with a traditional sampling scope *in averaging
mode* : it can be seen as a bank of samplers followed by a bank of lowpass
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