=  NOW 30 WPM  =  TEXT IS FROM AUGUST 2021  QST  PAGE 33 =

OPTIONAL S METER, AND A THIRD SETS THE LEVEL OF ATTENUATION WHEN A STRONG
SIGNAL IS PRESENT.  THE INPUT TO THE AGC CIRCUIT CONNECTS TO THE TOP OF THE
EXISTING RECEIVER VOLUME CONTROL, WHICH IS THE OUTPUT FROM THE AUDIO
PREAMP.  POTENTIOMETER R8 SETS THE THRESHOLD POINT WHERE AGC ACTION BEGINS.
THE SIGNAL IS AMPLIFIED BY Q1 AND RECTIFIED BY D1 AND D2.  THE RECTIFIED
SIGNAL CHARGES C6.  THE DC VOLTAGE LEVEL STORED ON C6 VARIES WITH THE
INCOMING AUDIO LEVEL.  IT IS THEN AMPLIFIED BY Q2 AND, IF DESIRED,
OPTIONALLY DRIVES THE POSITIVE INPUT OF A 1 MA FULLSCALE S METER.  THE
NEGATIVE S METER LEAD CONNECTS TO GROUND.  POTENTIOMETER R9 ADJUSTS THE
LEVEL TO CALIBRATE THE METER.  THE AMPLIFIED SIGNAL ALSO PASSES TO Q3,
WHICH IS CONNECTED TO THE RECEIVER BOARD AT R8 OF FIGURE 2.  AS SIGNAL
LEVEL INCREASES, Q3 BEGINS TO TURN ON.  AS INPUT SIGNAL LEVEL INCREASES,
THE AGC BOARD DRAWS MORE CURRENT.  LESS CURRENT FLOWS THROUGH D2 OF FIGURE
2 ON THE RECEIVER BOARD, SO GAIN DECREASES IN THE SECOND IF AMPLIFIER STAGE
AND THAT, IN TURN, LESSENS THE DETECTED AUDIO LEVEL.  YOU MUST MODIFY THE
RECEIVER, AS SHOWN IN FIGURE 2.  LIFT ONE END OF THE R8 RESISTOR AND INSERT
=  END OF 30 WPM TEXT  =  QST DE W1AW  <