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From: kjh@aludra.usc.edu (Kenneth J. Hendrickson)
Newsgroups: sci.electronics,rec.ham-radio
Subject: Re: A question about a PLL synth loop filter
Message-ID: <12890@chaph.usc.edu>
Date: 1 Nov 90 22:05:53 GMT
References: <1990Oct31.210242.20619@aplcen.apl.jhu.edu>
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In article <1990Oct31.210242.20619@aplcen.apl.jhu.edu> @aplvax.jhuapl.edu:mjj@stda.jhuapl.edu (Marshall Jose) writes:
%I have been trying to understand a passive loop filter I have twice seen used
%in ham radio construction articles.  It looks like this:
%
%
%     O---VVVVV----+-------+------O
%           R1     |       |
%                  |       >
%                  |       >  R2
%                  |       >
%                 ---      |
%                 --- C1   |
%                  |       |
%                  |      ---
%                  |      --- C2
%                  |       |
%     O------------+-------+------O
%
%
%                 C(as + 1)
%     H(s) = ---------------------
%               3     2
%              s  + ps  + qs + r
%

Your first clue, is that since you have two energy storage devices, that
you should have two poles.  When I solve this, I get:

                     c1r1 * s + 1
H(s) = ---------------------------------------------
       c1c2r1r2 * s^2 + (c2r2 + c1r1 + c2r1) * s + 1

Ken Hendrickson N8DGN/6      kjh@usc.edu      ...!uunet!usc!pollux!kjh