MFJ MFJ-752D Instruction Manual Download Page 4

 

peak  will  form  at  the  frequency  set  on  the  FREQUENCY  control.    The  more  the 
selectivity  is  increased,  the  more  pronounced  the  peak  will  become.    This  peak 
may be preferred for CW operation when extra audio is needed and low frequency 
signals are not a problem.  Because circuit gain rises in the LOW PASS mode, the 
input audio level may need to be reduced to prevent over driving the filter.  Gain 
on  frequencies  below  the  set  frequency  will  drop  as  selectivity  is  increased.  
Therefore, when using the LOW PASS mode for SSB, the SELECTIVITY control 
should not be set beyond the 2 o'clock position. 

HIGH PASS: 

HIGH PASS mode is set by turning the Function Selector to HIGH PASS (HP).  To 
remove  unwanted  low  audio  frequencies,  set  the  SELECTIVITY  and 
FREQUENCY controls for the desired response. 

  
 

AUXILIARY FILTER OPERATION 

 

PEAK:  

To set the auxiliary filter in the peak mode, simply push the FUNCTION button to 
the  IN  position.    Set  the  SELECTIVITY  control  to  about  center  range  and  adjust 
the  FREQUENCY  control  to  the  desired  signal.    Adjust  SELECTIVITY  and 
FREQUENCY  controls  alternately  for  the  best  signal  and  the  desired  bandwidth. 
In the peak mode, the auxiliary filter can be used to further enhance the primary 
filter  operation.    It  can  be  used  to  obtain  very  narrow  bandwidths  with  good  skirt 
selectivity and little ringing when the primary filter is in the peak mode, or to limit 
the  bandwidth  when  the  primary  filter  is  in  the  NOTCH,  LOW  PASS,  or  HIGH 
PASS  mode.    NOTE:  When  using  both  filters  in  the  PEAK  mode  with  narrow 
bandwidths,  the  best  skirt  selectivity  and  least  attenuation  will  be  obtained  by 
setting both the auxiliary and primary filter frequency controls to the same center 
frequency.    This  can  easily  be  done  by  first  peaking  the  desired  signal  with  the 
auxiliary FREQUENCY control and then peaking it with the FREQUENCY control 
on the main filter. 

 
NOTCH:  

NOTCH mode on the auxiliary filter is set by pushing the FUNCTION button to the 
OUT  position  with  the  primary  filter  in  any  mode.    Set  the  SELECTIVITY  control 
about center range and adjust the FREQUENCY control to remove the unwanted 
signal.    SELECTIVITY  and  FREQUENCY  should  be  adjusted  alternately.  
Remember  at  high  selectivity  on  NOTCH,  the  NOTCH  frequency  is  difficult  to 
locate  and  the  FREQUENCY control must be tuned very carefully.  The auxiliary 
notch filter is used to remove an unwanted signal in the passband of the primary 
filter.  It can remove a heterodyne from SSB or AM signal when the primary filter is 
set to PEAK, LOW PASS, or HIGH PASS mode.  It can also be used to notch out 
an adjacent CW signal which is too close to be removed by peaking the filters. 

 
 

Summary of Contents for MFJ-752D

Page 1: ...UAL CAUTION Read All Instruction Before Operating Equipment MFJ ENTERPRISES INC P O BOX 494 MISSISSIPPI STATE MS 39762 USA 925 0037D 752D REV 1 COPYRIGHT 2010 MFJ ENTERPRISES INC MFJ SIGNAL ENHANCER II Model MFJ 752D ...

Page 2: ...ceiver or receiver to the MFJ 752D Use an RCA phono plug to connect to the filter input There are two inputs on the MFJ 752D allowing connection to two receivers for greater convenience The input is selected by the push button switch on the back of the MFJ 752D 3 Connect a speaker to the filter using shielded wire with a RCA phono plug at the filter speaker output For best results use a 4 to 16 oh...

Page 3: ...he NOTCH filter is approximately 70 dB Notch frequency is adjustable from approximately 300 Hz to 3000 Hz The primary notch filter can be set to the NOTCH mode by setting the Function Selector to NOTCH Set SELECTIVITY control to the 9 o clock position Adjust FREQUENCY control to remove the CW signal or heterodyne Increase SELECTIVITY clockwise to narrow the bandwidth of the notch Readjust FREQUENC...

Page 4: ...eration It can be used to obtain very narrow bandwidths with good skirt selectivity and little ringing when the primary filter is in the peak mode or to limit the bandwidth when the primary filter is in the NOTCH LOW PASS or HIGH PASS mode NOTE When using both filters in the PEAK mode with narrow bandwidths the best skirt selectivity and least attenuation will be obtained by setting both the auxil...

Page 5: ... and turn the SELECTIVITY and FREQUENCY controls to minimum counter clockwise 2 With high selectivity the filter may have a tendency to ring in peak and lowpass modes If this occurs decrease the selectivity 3 Due to the very high internal filter gains in the LOW PASS mode with maximum selectivity and frequency the filter may OSCILLATE If this occurs reduce SELECTIVITY and FREQUENCY controls until ...

Page 6: ... 1V p p and adjust generator frequency control s for a null minimum amplitude Null should occur at about 3000 Hz 4 Switch Primary Function Selector to PEAK 5 Increase Primary SELECTIVITY control to maximum 6 Adjust R319 10K High Tracking trimmer for maximum amplitude 7 Set generator frequency to 500 Hz 8 Set primary SELECTIVITY control to 3 o clock 9 Set primary filter to NOTCH and adjust primary ...

Page 7: ...6 MFJ 752D Schematic Diagram ...

Page 8: ...is warranty is NOT void for owners who attempt to repair defective units Technical consultation is available by calling 662 323 5869 5 This warranty does not apply to kits sold by or manufactured by MFJ Enterprises Inc 6 Wired and tested PC board products are covered by this warranty provided only the wired and tested PC board product is returned Wired and tested PC boards installed in the owner s...

Reviews: