On Tue, 16 Mar 2004 19:54:27 -0600, John Fields
wrote:

On Tue, 16 Mar 2004 20:26:15 +0000, Paul Burridge
wrote:


An argument over semantics, then. AFAIC it's not filtering as such.
It introduces a high degree of selectivity, certainly. But when
someone says "filtering" I assume they're taking about a pi-network or
something of that sort, between stages or at the end of a chain of
stages.

---
Any network which exhibits frequency selectivity is a filter, whether or
not you're concerned about whether or not it is or is not.

Think about it... from the lowly filter capacitor to the exalted
brickwall filter, they're all discrimating against a frequency or a set
of frequencies which we have told them we don't want them to let us see.

Filters, every one.

Just for grins, take a little trip over to a.b.s.e. (same subject
heading)and take a look at what John Larkin's series resonant filter
feeding a parallel resonant filter strategy looks like as far as
allowing you to get a fifth harmonic from a fundamental square wave
goes.


That's just a standard bandpass. What you do is pick a normalized
lowpass filter that has the response shape you like, say a Tchebychev
(I know... various spellings) and scale it to the impedance Z' and
bandwidth W' you want. Then series resonate each L with a C, and
parallel resonate each C with an L, both at some desired center
frequency. Voila (pardon my French) a bandpass that's 2W' wide.

There's no real reason to cascade lossy Q-killing tuned transistor
stages when you can put all your Ls and Cs in one place.

John