From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: How does a mixer work?
Date: Wed, 23 Oct 2002 11:26:05 GMT
NNTP-Posting-Date: Wed, 23 Oct 2002 04:26:05 PDT
John Woodgate wrote:
> I read in sci.electronics.design that John S. Dyson
> wrote (in ) about 'How does a mixer
> work?', on Tue, 22 Oct 2002:
> > Additionally,
> >normal linear transforms (where spectrum analysis is allied to the fourier
> >kind of transform) don't generally work well WRT nonlinear operations (or
> >with signals that have time varying characteristics.)
> Again, this is confused and misleading. You can certainly, for example,
> do Fourier analysis on a half-wave or full-wave rectified sine wave,
> which is the result of a non-linear process.
I think he is refering to the problem familiar to servo engineers having
to do with instrumental methods of Fourier analysis. In particular, some
dynamic analyzers use white noise to excite a system, collect data for a
time, then apply a DFT and finally display the result. This is
unworkable on many servo systems because the spectrum that results is
highly polluted with modulation products that are of no interest
whatever. Much more meaningfull results are obtained using swept sine
excitation and using single point DFTs at frequency points in the sweep.
This eliminates meaningless garbage from the spectrum. Dynamic analyzers
from Agilent and SRS of the better sort have swept sine available.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org