As described in the previous post, here are the results from the replica of the IF amp circuit for the mighty Kenwood KR-9600 with LA1222:
Attachment 1 and 2: S21 and group delay for the four 280kHz ceramic filters in cascade,-3db bandwidth is 210KHz, shape factor = 1.96 at 6db/60db;
Attachment 3: two 280KHz ceramic filter+ 5 pole Chebyshev LC filter, -3d bandwidth = 220KHz, shape factor = 2.15 at 6db/60db
Both configurations have fairly flat phase shift linearity and they work well with the 6-gang stereo tuner, not too wide or too narrow.
In my next stage of nerdy experiment, I will build a 7-pole Butterworth 10.7MHz IF of bandwidth of 280kHz so that I will have total of 12 poles in the IF amp combined with the 5-pole Chebyshev.
The Butterworth has better phase shift linearity than Chebyshev but it also has rounder shoulders. The 7-pole Butterworth should make the roll-off as steep as the 5-pole Chebyshev filter.
Attachment 4: LA1222 IF amp, TA7303 IF amp and demodulator, and TA7343 MPX decoder. I will need to experiment with different IF amp as the TA7303 tends to get overloaded easily with MPX audio distortion. There is plenty of gain and selectivity with the LA1222 IF amp.
Attachment 5: is the IF response curves of the RIMO filter designed by Richard Moddafferi for the highly regarded Mcintosh MR-78. Note its shape has Bessel filter like rounded-shoulders. The -3db bandwidth is very narrow in both normal, narrow and super narrow configurations. According to the MR-78 service manual, the -6db bandwidth are 150kHz for normal and 130Khz for narrow which would chop off some of the MPX audio. It would be good for DX and overcrowded FM band with adjacent strong and weak stations. For stereo MPX fidelity, I think they are too narrow.
Here is his dissertation:
https://digitalcommons.njit.edu/thes...=PDFCoverPages
It seems that he moved the poles in S-plane to achieve the best flatness of the group delay response using a Fortran programme. The Rimo filter was introduced at the time that the ceramic filters started to become the norm. Since no other tuners used Rimo filter, its complexity and costs probably outweight its benefits.
Attachment,