‰  NOW 40 WPM  ‰  
SCAF 1, THE MANUAL DIRECTS YOU TO ADJUST AN INTERNAL POTENTIOMETER R17,
LOWER CENTER OF THE PC BOARD IN FIGURE 4 TO EQUALIZE THE IN LINE AND
BYPASSED AUDIO LEVELS.  I FOUND THAT IF I CHANGED TO DIFFERENT HEADPHONES
OR SPEAKERS THAT WERE NOT IDENTICAL IN IMPEDANCE, I WOULD NORMALLY HAVE TO
READJUST R17.  WERE I TO CHANGE LOADS OFTEN, I WOULD PROBABLY DRILL A SMALL
HOLE IN THE COVER TO MAKE THE ADJUSTMENT MORE CONVENIENT.  ONCE THE
INTERNAL POTENTIOMETER IS ADJUSTED, OPER

WAS MINIMAL.  FOR STRONG INTERFERING SIGNALS, YOU CAN TURN OFF YOUR
RECEIVERS AGC AND CONTROL THE LEVEL WITH YOUR RF GAIN CONTROL.  I ALSO
EXPERIMENTED WITH THE MFJ 752D LOW PASS AND HIGH PASS FILTER MODES AS THESE
HELP REDUCE HIGH OR LOW FREQUENCY NOISE.  AS THE ARRL LAB DATA SHOWS, THE
FREQUENCY RESPONSE SHIFTS WHEN THE SELECTIVITY CONTROL IS ADJUSTED IN BOTH
THE LOW PASS AND HIGH PASS MODES.  HOWEVER, AS PART OF THE TUNING PROCESS
BOTH THE SELECTIVITY AND FREQUENCY KNOBS ARE NORMALLY TUNED FOR BEST
SOUNDING AUDIO.  IN MY OPINION, CAREFUL USE OF THE PEAK FUNCTION WAS EASIER
AND PROVIDED MORE EFFECTIVE BANDWIDTH LIMITING AND FILTERING.  WHILE THE
PEAK MODE PROVIDES THE NECESSARY SELECTIVITY FOR MOST USES, THE NOTCH MODE
CAN HELP WHEN OPERATING WITH A CLOSE IN INTERFERING CW SIGNAL.  AGAIN, A
STRONG INTERFERING SIGNAL CAN CAPTURE OR PUMP YOUR RECEIVERS AGC UNLESS THE
INTERFERING SIGNAL IS AT LEAST 6 DB BELOW THE DESIRED SIGNAL.  TABLE 4
INDICATES THAT THE ARRL LAB ACHIEVED 41 DB OF NOTCH PERFORMANCE FOR A
SIGNAL JUST 200 HZ AWAY FROM THE DESIRED SIGNAL.  HOWEVER, I FOUND THAT
ACHIEVING THIS LEVEL OF NOTCH REDUCTION REQUIRED CRITICAL TUNING OF THE

USING THE MFJ 752D ALL MFJ 752D INPUTS AND OUTPUTS ARE LOCATED ON THE REAR
PANEL.  A CABLE CONNECTS YOUR RECEIVERS SPEAKER OUTPUT OR HEADPHONE JACK TO
ONE OF THE MFJ 752DS RCA AUDIO INPUTS, AND A 4 16 SPEAKER CONNECTS TO THE
MFJ 752D SPEAKER OUTPUT A PHONO JACK.  EITHER MONO OR STEREO HEADPHONES MAY
BE PLUGGED INTO THE 3R5 MM HEADPHONE JACK.  PLUGGING IN HEADPHONES WILL NOT
MUTE THE SPEAKER OUTPUT.  FINALLY, 9 18 V DC CONNECTS TO THE 2R1 MM COAXIAL
DC JACK.  AS YOU CAN SEE FROM THE PHOTO AND TABLES, THE MFJ 752D HAS MANY
DIFFERENT FILTER OPTIONS MEANING A LOT OF ADJUSTMENTS, SOME OF WHICH ARE
INTERACTIVE.  SO THERE IS A LEARNING CURVE IN ORDER TO ACHIEVE THE BEST
PERFORMANCE.  I FOUND IT EASIEST TO START WITH THE PRIMARY FILTER, USING
JUST THE PEAK FUNCTION.  IT WAS EASY TO ADJUST THE PRIMARY FILTER FREQUENCY
AND SELECTIVITY CONTROLS FOR THE BEST SOUNDING AUDIO IN THE PRESENCE OF
CLOSE IN INTERFERENCE.  WHEN ADDITIONAL SELECTIVITY WAS REQUIRED, I ENABLED
THE PEAK MODE OF THE AUXILIARY FILTER AND ADJUSTED THE AUXILIARY FREQUENCY
AND SELECTIVITY CONTROLS FOR BEST PERFORMANCE.  I COULD QUICKLY HOME IN ON
THE BEST SOLUTION BY GOING BACK AND FORTH BETWEEN THE PRIMARY AND AUXILIARY
FILTER CONTROLS.  KEEP IN MIND THAT THIS IS AN AUDIO FILTER, SO A STRONG
INTERFERING SIGNAL CAN CAPTURE YOUR RECEIVERS AGC.  I FOUND THAT IF THE
INTERFERING SIGNAL WAS AT LEAST 6 DB BELOW THE DESIRED SIGNAL, AGC CAPTURE
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ