‰  NOW 40 WPM  ‰  TEXT IS FROM AUGUST 2006 QST  PAGES 52, 53 AND 97  ‰

HANDS ON RADIO EXPERIMENT 43 RF OSCILLATORS, PART 1 IN EXPERIMENT 17 ON THE
PHASE SHIFT OSCILLATOR WE EXPLORED THE IDEA OF USING PHASE SHIFT AND
FEEDBACK TO TURN AN AMPLIFIER INTO A SELF SUSTAINING OSCILLATOR.  ITS NOT A
BAD IDEA TO GO BACK AND SKIM THAT COLUMN.  THIS MONTH WE TURN PRO AND MOVE
HIGHER IN FREQUENCY TO THE WORLD OF RF OSCILLATORS.  IN A SENSE, THIS IS
THE FUNDAMENTAL BUILDING BLOCK OF RADIO WITHOUT AN OSCILLATOR THERE WOULD
BE NO SIGNALS TO AMPLIFY OR RECEIVE.  ALONG WITH LEARNING ABOUT
OSCILLATORS, YOULL LEARN ABOUT A NEW WAY TO BUILD RF CIRCUITS.  THIS IS A
TWO PART EXPERIMENT IN THIS INSTALLMENT WELL DISCUSS HOW RF OSCILLATORS
WORK.  NEXT MONTH WELL BUILD AND TEST ONE.  TERMS TO LEARN BARKHAUSEN
CRITERION FOR AN OSCILLATOR TO OSCILLATE, THE PRODUCT OF GAIN AROUND THE
FEEDBACK LOOP MUST BE EQUAL TO OR GREATER THAN UNITY 1.  LOOP GAIN THE
AMOUNT OF TOTAL GAIN MEASURED ALL THE WAY AROUND A FEEDBACK LOOP.  THE
OSCILLATOR A REVIEW AN OSCILLATOR CONSISTS OF A MEANS OF AMPLIFICATION A
TRANSISTOR, INTEGRATED CIRCUIT OR VACUUM TUBE AND A FEEDBACK NETWORK.  THE
FEEDBACK NETWORK SHOWN AS AN LC RESONATOR IN FIGURE 1 IS DESIGNED SO THAT
‰  FROM PAGE 97  ‰
JH2FXK/339 JH2RMU/340 JH3AEF/342 JH4GNE/339 JH6IMI/ 338 JH7QXL/ 340
JH8CFZ/339 JH8GWW/343 JH8NBJ/340 JJ2LPV/339 JL1XMN/ 340 JM1GYQ/ 339
JN1VNW/339 JR1WCT/344 JR9LKE/335 K0BS/358 K0FF/348 K0GSV/355 K0GT/343
‰  QST DE W1AW  ƒ

AT THE FREQUENCY OF INTEREST, THE PRODUCT OF AMPLIFIER GAIN AV IN FIGURE 1
AND FEEDBACK RATIO, IS EQUAL TO OR GREATER THAN 1.  AV IS ALSO KNOWN AS
LOOP GAIN, THE TOTAL GAIN EXPERIENCED BY A SIGNAL ALL THE WAY THROUGH THE
AMPLIFIER, THE FEEDBACK NETWORK AND BACK TO THE INPUT.  THE REQUIREMENT
THAT AV 1 IS FORMALLY KNOWN AS THE BARKHAUSEN CRITERION.  ITS IMPORTANT TO
NOTE THAT 1 IN THIS CASE MEANS AN AMPLITUDE OF 1 AND A PHASE DIFFERENCE OF
0.  IF AV IS NEGATIVE INVERTING, THEN B MUST ALSO BE NEGATIVE, MEANING THE
FEEDBACK MUST HAVE A 180 PHASE SHIFT.  SIGNALS OF THE RIGHT FREQUENCY WILL
BE AMPLIFIED, A PORTION FED BACK TO THE AMPLIFIER INPUT, AMPLIFIED AGAIN,
AND SO ON, BECOMING SELF SUSTAINING AND CREATING A STEADY OUTPUT SIGNAL.
IF THE AMPLITUDE OF THE FEEDBACK IS SUFFICIENT, BUT IF THE PHASE DIFFERENCE
IS NOT EXACTLY RIGHT THEN THE RETURNED PORTION OF THE OUTPUT SIGNAL BECOMES
PROGRESSIVELY FARTHER AND FARTHER OUT OF PHASE ON EACH TRIP.  THE RESULT IS
THAT THE OSCILLATORS OUTPUT CONSISTS MOSTLY OF A FUNDAMENTAL FREQUENCY PLUS
‰  FROM PAGE 97  ‰
K0GX/335 K0HRF/344 K0IUC/350 K0JGH/347 K0JN/357 K0JY/346 K0MN/349 K0NN/347
K0QC/342 K0WK/345 K1AR/349 K1BD/346 K1BV/359 K1EFI/355 K1IK/350 K1JU/340

SHIFT IS PROVIDED BY A RESONATOR SUCH AS A PARALLEL LC CIRCUIT.  MEET MSSRS
HARTLEY AND COLPITTS BACK IN THE 1920S, TWO FELLOWS BY THE NAMES OF HARTLEY
AND COLPITTS CAME UP WITH THE DIFFERENT OSCILLATOR CIRCUITS OF FIGURE 3
THAT BECAME POPULAR IN RADIO DESIGNS.  I
‰  FROM PAGE 97  ‰
K4HJE/362 K4IQJ/343 K4JAF/342 K4JLD/348 K4JP/354 K4JRB/369 K4KJZ/345
‰  END OF 40 WPM TEXT  ‚