[sdiy] Passive filters and impedances

[Neil Johnson]

HI Phil,

An alternative that could be easier to get started with would be to use a
> series of ABCD matrices. That way you can solve for any number of stages
> too.
>

Thanks for stirring up some ancient memories!

After a quick refresher, e.g.,
http://www.engr.sjsu.edu/rkwok/EE172/Microwave_Network.pdf

and some fun with wxmaxima it is actually quite easy to bash in the
equation for the filter, and then you can flip it around to work out the
transfer function.  In this case the filter is represented as:

matrix([1,R1],[0,1]).matrix([1,0],[%i*w*C1,1]).matrix([1,R2],[0,1]).matrix([1,0],[%i*w*C2,1]).matrix([1,R3],[0,1]).matrix([1,0],[%i*w*C3,1]).matrix([1,0],[1/Rimp,1]);

and turns into something that has quite a few brackets, and as Murphy would
have it the A term has the most.

Cheers,
Neil
--
http://www.njohnson.co.uk
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