George, W5YR's IF Filter Performance Page

now updated with IC-756Pro II data and new graphic plot format

This page allows side-by-side comparison of IF filter passband characteristics (bandwidth, passband ripple and shape factor) between the IC-756Pro II DSP IF filters and equivalent analogue crystal filters in an IC-765. Two IC-746Pro filters are also shown for comparison purposes.
Test Configuration: The ACC1 line audio output of the IC-756Pro II, and the speaker audio output of the IC-765, are connected via a Behringer MX-802A mixer to the sound-card line input of a computer running an FFT spectral-analysis program. This program captures the noise spectrum as an amplitude/frequency plot of the combined audio response functions of the IF filters and audio systems of the receivers. Note that the audio system responses play a role in determining the overall response functions as plotted.
Note on IC-756Pro II USB/LSB:  As the IF bandpass is symmetrical, the LSB and USB plots for the PRO are identical in practice as well as theory. Thus, the USB plot is shown for USB and LSB.
Note on mixer settings: All spectra were taken with the MX-802A EQ controls set "flat" so that no pre-emphasis or de-emphasis effects are present.
Note on stopband attenuation: Using the new spectral-analysis program, the filter plots now show almost 60 dB of ultimate rejection (stopband attenuation) from passband to floor. The no-signal sound-card noise level lies between -110 and -120 dBr. Nonetheless, there are some low-frequency spikes on the plots. I believe that 99% of this is due to noise and trash picked up from within the computer and on the PCI bus.
Notes on indicators:  BPF = Bandpass Filter Shape Factor.  TPF = Twin Peak Filter selected.

Relevant Links

George, W5YR's Notes on Filtering & DSP
Behringer GmbH
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Copyright 2001-2018, George T. Baker, W5YR

Page created by A. Farson VA7OJ/AB4OJ. Last updated: 06/15/2018