‰  NOW 35 WPM  ‰  TEXT IS FROM JANUARY 2015 QST  PAGE 49‰

LOSCOPE WILL SHOW 0R56 V PEAK TO PEAK.  NOTE THE POSITION OF THE PC VOLUME
SLIDER CONTROL SO YOU CAN RETURN TO THIS SETTING IF IT IS CHANGED.  THIS
LEVEL, WHILE NOT ABSOLUTELY CRITICAL, SHOULD BE IN THE RANGE OF 0R14 TO
0R24 V RMS.  THIS ADJUSTMENT CAN BE USED TO INCREASE OR DECREASE THE POWER
OUTPUT OF THE TRANSMITTER OVER A SMALL RANGE.  NEXT, WITH AUDIO SIGNAL
REMOVED AND 12 V DC POWER OFF, ADJUST BOTH BIAS POTENTIOMETERS R18 AND R19
FOR 0 TO GROUND.  SWITCHING TYPE MOSFETS DO NOT HAVE PRECISELY SPECIFIED
GATE VOLTAGE THRESHOLDS.  TYPICALLY THEY VARY FROM 2 TO 4 V.  HENCE, THE
BIAS FOR EACH MOSFET NEEDS TO BE SET SEPARATELY.  STARTING AT ZERO BIAS
WILL ENSURE THAT THE MOSFETS ARE OFF INITIALLY.  THEN INCREASE THE BIAS
VOLTAGE TO THE POINT WHERE THEY ARE JUST BARELY CONDUCTING.  HERE IS THE
SIMPLE PROCEDURE.  FIRST CONNECT A 50 RF LOAD RESISTOR ACROSS THE ANTENNA
TERMINAL.  CONNECT YOUR VOM DC MV SETTING BETWEEN GROUND AND TEST POINTS
TP1 AND TP2 IN TURN TO MONITOR FOR THE ONSET OF CONDUCTION OF EACH OF THE
MOSFETS.  WITH AUDIO SIGNAL REMOVED, TURN ON THE 12 V DC TO THE
TRANSMITTER.  ADJUST R18 FOR A 1 TO 2 MV READING AT TP1 ON THE VOM.  THIS
CORRESPONDS TO ABOUT 1 TO 2 MA OF CURRENT IN Q2.  NOW MOVE YOUR VOM TO TP2
AND ADJUST R19 FOR 2 TO 3 MV.  A HIGHER SETTING WILL REDUCE IMD, BUT
TRANSISTORS WILL GET HOTTER.  YOUR WSPR TRANSMITTER IS READY TO GO.  WSPR
‰  END OF 35 WPM TEXT  ‰  QST DE W1AW  ƒ