[sdiy] why 10V

[Magnus Danielson]

From: "jhaible" <jhaible at debitel.net>
Subject: Re: [sdiy] why 10V
Date: Sun, 21 Sep 2003 12:09:33 +0200

> > Clipping (what Jürgens question was aiming at) is nonlinear.
> 
> That's true. But I would still say the reason of my initial question was
> to _avoid_ clipping / nonlienar behaviour. (;->)

He was - I spotted it early out... before we deviated into theory-land.

> > One treats
> > transforms like Hilbert transforms in a linear theory where all
> > intermediate values can be infinitesimal. But in real circuits thats not
> > the case.
> 
> I thought the limit was one of causality, not linearity.
> For a perfect 90deg shift over all frequencies, you'd need to "see into
> the future". If you have a band limited signal (especially omitting
> the lowest frequencies), you can introduce a _delay_ for your signal,
> to compensate for this "looking into the future". The lower your
> frequency range, the more delay you would need. For DC, you would
> need infinite delay. (Just imagine what a 90deg phase shifted
> DC voltage would look like! - I'm certain Magnus could give
> the answer right away, without looking into the books. Hi Magnus!)

Yes, you are right... I can answer this... and also, by books is back in 
Stockholm, Sweden and not here in Sophia-Antipolis, France.

Yes, you need to have the full time-history to do it "according to the book"
(or in this case, according to me). You can create approximations which doesn't
need to break with physics and integrate over the full lifetime of the 
universe.

> What looks like theory straight from the ivory tower (HT of DC) has
> a very practical conclusion in the real world: All these Frequency
> Shifters that offer two dome-filter-inputs instead of a local
> quadrature oscillator, will not be capable of very low amount
> of frequency shift. (No slow infinite phasing, for instance)

Yes. I agree.

Cheers,
Magnus - sometimes called "Captain Signaltheory" by some people...