2019-10-23   13:42:03

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--- a Simple Collection of Project Schematics ---
     This page loads slowly 
for developmental details goto the specific pages for each schematic (click)



1.  Pre-Amp
2.  Roofing-Triad Differential Filter 
3.  Active-Log_limiter 
4.  Quad-MFB audio filter , variable f()
5.  Double-Notched Differential-Phase Filter
6.  Sharp Q20 MFB variable Filter
6.  Audio out 0.5 W class-B 


   Each module presented can be constructed on a proto-board

    and used as a stand-alone circuit.
Intra-State impedances are well matched
Standard  Signal  Input/Output  is 1 V audio

for developmental details goto the specific pages for each schematic (click) 






This is a Research Project about  Phase-Filters for Narrow Channel CW reception,


   This is a Study about Differential Phase-Filters and includes these topical sections : 
    Roofing Triad Filter    &
   Active Log-Limiter    &    MultiFeedBack Filters    &   Differential Phase Filters   &   Audio Amp.           

       *** Designed for Easy Construction and Easy tuning and Superior CW audio filtering.
       *** Constructed and used daily for Amateur Radio CW (morse code) Operations on the Radio Bands. 
       *** The AFX CW audio filtering has near Digital Signal Processing quality as presented to the Ear.
      *** The vintage  LM324 OpAmp was chosen because the project frequency response and gain requirements are within bounds.

       *** Note that OpAmp null and balance trim-pots are not shown, and common by-pass caps not shown. 
       *** (1) for simplification
       *** (2) circuit designs are self-balancing and produce symetrical waveforms.


Left is a Magnitude Plot of a typical  Dual-Notch Circuit.                           Right is a Bode Plot of a typical PassBand group. 




This is the basic equation for the Multiple-FeedBack active filter which is used dominantly. 
Advantages are simple f(0) variation, which allows easy alignment of filters. 
R(2) is the only component that needs adjustment for a +/- 20% change.
    [Q will change only as the square-root of the delta-f(). ] 



   the   AFX  B.A.S.I.C.  Schematic
(first version) 



 AFX'V'   Single Roof Filter   Schematic 
with Narrow Dual-Notch and Wide-Integrated Stages
Early version  


 the    AFX'V'  with  Variable f() PassBand   Schematic  (Best of Class)
with Manual controlled Variable f(0)
Three Roof Filters
(advanced version)  




 the    AFX'V'  with Variable f() PassBand     (Best of Class)
with jFET controlled Variable f(0) and Three Roof Filters
(advanced version)




the   AFX  Roofing-Triad-Filter





the   AFX  Active Limiter 











the  AFX  Quad-MFB Filter details
Multi-FeedBack Active Filter Standard
(early basic version) 



the   AFX  Differential-Phase Filter  and Q20 Sharp filter







The AFX Audio Driver
(with forced 3rd harmonic distortion) 




  ******* Manual Tuning  via Four 5K panel mounted pots. 
    ******* designed to control all four Filter f(0), manually, for initial set-up.



*** AFV_3RL-v2F-vQ-v1-S  design : 

***  (1) with Three Roof Filters 
***  (2) with only Two MFB filter stages ( not sufficient for dual notch )
***  (3) with R(freq) controlled by a Two-Gang Pot 





Schematic shows
24 All-Pass filters
used to
replace two MFB Active PassBand Filters

*** results are Very Good


Schematic shows
8 All-Pass filters
used to replace two MFB Active PassBand Filters

*** results are Usable, OK.
*** Compared to the "AFV-3RL-V4F-D-VQ" version
(1) BW @ -3dB is wider ; 160 Hz vs 80 Hz.
(2) Dual Notch BW is wider ; 380 Hz vs 330 Hz.
(3) Variability of f(0) is much narrower ; +/- 50 Hz  vs +/- 100 Hz 



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