On Tue, 16 Mar 2004 19:43:24 -0800, John Larkin
wrote:

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

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.

Okay, well at least I can see this one! Not sure about the SA trace,
though. Came out clearly enough but I'm not sure what you were trying
to prove by it. As for the 'scope traces, there doesn't seem to be any
phase correlation between the two and you don't indicate at what point
the probe was inserted. The square wave r/f slopes look a bit tardy,
too. What was the active device you used to generate them?

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.

It's basically the same type as Reg's program designed for me. That
was built on Sunday, tested and found to be bang on the money and
later today I shall try to see if it can be used to 'extract' the
elusive 5th. I have to admit I'll be surprised if there's nothing
there at all, but we'll have to wait and see. Don't touch that dial!
:-)



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