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
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