On Sun, 2006-03-26 at 09:12 -0500, Bill Tippett wrote:
K0CQ:
>
> > A filter need not have square corners, nor a ringing response. A
> Butterworth filter
> will take at least 5 times the speed of a square cornered filter and
> a Bessel will do
> better than that. The DSP filters in common use do far better than
> similar analog
> filters because the DSP filters have far higher orders allowing a
> better approximation
> of the amplitude response desired along with a better time response.
> This can be
> accomplished in analog filters too, but hardly ever is because of the
> significantly
> greater filter complexity.
>
> So these 10 Hz filters will pass
> the information contained in a 200 Hz signal.
> Very interesting. Since Bessel died in 1846
> I'm surprised Nyquist, Shannon and Hartley
> had not heard of this when they published
> their work at Bell Labs 100 years later.
>
> 73, Bill W4ZV
>
Not quite what I said. The Bessel filter will pass the components of that 200
Hz signal
that fit in its pass band without adding the artifacts of ringing. And that
Bessel
filter will pass most of that 200 Hz signal because the skirts of the Bessel
filter are
broad and gently sloped. Within the limits of minimum parts designs (as most
analog
filters are) one trades off steep skirts for a better time response. The
Tchebyshev and
Caurer filters approximate a square bandpass shape far better but at the cost
of lots of
ringing in the time response.
I doubt Bessel defined any thing in filters, its just one of his functions is
used to
define the Bessel filter response.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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