MFJ MFJ-752D Instruction Manual Download Page 3

 

 

AUXILIARY FILTER: 
Function Switch: 

To  select  the  PEAK  function  push  button  to  the  IN  position.    To 
select the NOTCH function push button to the OUT position. 

 
Frequency Control:  Adjusts  the  center  frequency  of  the  auxiliary  peak  and  notch 

circuits between approximately 300 Hz to 3000 Hz. 

 
Selectivity Control:  Adjusts the bandwidth of the auxiliary circuits from 40 Hz to almost 

flat.    To  select  the  PEAK  function  push  IN  this  control.    To  select 
the NOTCH function push out this control. 

 
 

PRIMARY FILTER OPERATION 

 

PEAK:  

Turn  Function  Selector  to  PEAK.    Set  the  SELECTIVITY  control  to  about  the  10 
o'clock  position.    Adjust  FREQUENCY  control  for  maximum  response  to  the 
desired signal.  Selectivity can be increased by turning the SELECTIVITY control 
clockwise.    FREQUENCY  and  SELECTIVITY  control  should  be  adjusted 
alternately to obtain maximum selectivity and best signal intelligibility.  The PEAK 
mode can be used on CW to narrow in on a signal and greatly reduce unwanted 
signals.  Peak mode is also useful on wider bandwidths such as RTTY and SSB.  
Adjust SELECTIVITY until the desired signal just fills the passband and interfering 
signals are reduced. 
 

NOTCH:  

The  depth  of  the  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 FREQUENCY control if necessary. 
The unwanted heterodyne should become weaker and the desired signal become 
clearer  as  notch  selectivity  is  increased.    At  high  selectivity  on  NOTCH,  the 
FREQUENCY  control  tuning  is  very  critical  and  the  notch  frequency  is  hard  to 
locate.    If  the  SELECTIVITY  control  is  rotated  past  the  3  o'clock  position 
clockwise,  the  NOTCH  depth  will  decrease.    NOTCH  mode  is  very  helpful  in 
removing heterodynes, stations tuning up on your QSO, or CW signals on or near 
your  frequency.    The  NOTCH  can  be  used  very  effectively  on  AM  when  two 
stations  are  heterodyning  one  other.    The  heterodyning  can  be  reduced  by 
notching out the interfering tone. 

 
LOW PASS: 

LOW  PASS  cutoff  is  adjustable  from  approximately  300  Hz  to  3000  Hz  with  the 
FREQUENCY  control.    The  SELECTIVITY  control  adjusts  the  steepness  of  the 
cutoff.    LOW  PASS  mode  is  useful  in  reducing  annoying  high  frequency  static, 
hiss  and  splatter.    When  selectivity  is  increased  beyond  the  2  o'clock  position, a 

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...

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