1. Chapter 21
Oscillators

2. Objectives Explain what occurs during an oscillation cycle.
Identify various oscillators.
Discuss and compare the Armstrong oscillator and the Hartley oscillator.
Outline the operation of the crystal oscillator and the power oscillator.
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3. Basic Oscillators Made up of: Cycle of voltage amplitude
Wave-producing circuit
Amplifier
Feedback circuit
Cycle of voltage amplitude
Cycle passes in one period
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4. Sustaining Oscillation
Regenerative feedback, or positive feedback
Enough feedback voltage amplitude to replace energy lost
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5. Armstrong Oscillators
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6. Step One Current flows from B- to B+ © Goodheart-Willcox Co., Inc.
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7. Step Two First half-cycle of oscillation © Goodheart-Willcox Co., Inc.
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8. Hartley Oscillators © Goodheart-Willcox Co., Inc.
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9. Hartley Oscillators (Cont.)
Used in radio receivers and transmitters
More stable than Armstrong oscillators
Radio frequency choke (RFC)
Series fed oscillators
Shunt fed oscillators
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10. Shunt Fed Oscillators
No dc path through coil L1 for emitter-collector current
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11. Review What is an oscillator?
Electronic circuit that generates an ac signal at a desired frequency
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12. Review What is a complete set of events in a repeated series called?
A cycle
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13. Review
What differentiates a Hartley oscillator from other oscillators?
The tapped coil
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14. Review What are the two types of Hartley oscillators?
Series fed oscillators and shunt fed oscillators
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15. Other Oscillators Colpitts oscillators Crystal controlled oscillators
Power oscillators
Operation amplifier oscillators
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16. Colpitts Oscillators Similar to Hartley oscillators
Split stator capacitor
Ganged capacitor
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17. Crystal Controlled Oscillators
Radio communications, broadcasting stations
Piezoelectric effect
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18. Crystal Controlled Oscillators (Cont.)
Crystals control transmitter frequency
Crystal ovens
Crystal added to feedback circuit
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19. Crystal Controlled Oscillators (Cont.)
Crystal used instead of inductor in the tank circuit of Colpitts oscillator
Pierce oscillators
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20. Additional Uses for Crystals
Two crystals producing two different frequencies for measuring temperature
Timing devices
Signal generators
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21. Power Oscillators
Collector load of each transistor is primary of transformer
Imbalance in conductivity starts oscillation
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22. Op Amp Oscillators Crystal used in feedback circuit
NAND gate starts op amp output
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23. Wien Bridge Oscillators
Use positive and negative feedback
Balance of feedback in circuit crucial
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24. Radio Detection and Ranging (Radar)
Existence of electromagnetic waves that travel at the speed of light
Advances occurred prior to World War II
Microwaves are transmitted out of radar dish in energy pulses
When waves strike reflective material, some is reflected back
Types of radar
Pulsar radar
Continuous-wave radar
Doppler radar
FM radar
Some planes are “invisible” to radar
Stealth bombers
Stealth fighters
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25. Review
What is the distortion in a crystal caused by a voltage applied to the surface of a crystal?
Piezoelectric effect
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26. Review What is a Pierce oscillator?
A Colpitts oscillator that uses a crystal in place of the inductor in the tank circuit
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27. For Discussion
Compare and contrast an electronic oscillator and a clock pendulum.
Explain the operation of a Hartley oscillator.
Why are crystal oscillators used in many commercial transmitters?
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28. Glossary Armstrong oscillator Colpitts oscillator
An inductive feedback oscillator.
Colpitts oscillator
A basic type of oscillator characterized by tapped capacitors in the tank circuit.
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29. Glossary Crystal controlled oscillator Crystal oven
Circuit with a stable high frequency, used in radio communications and broadcasting stations.
Crystal oven
Maintains a constant temperature of crystals used to control transmitter frequency.
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30. Glossary Cycle Ganged capacitor
1. Set of events occurring in sequence One complete reversal of an alternating current from positive to negative and back to the starting point.
Ganged capacitor
Two capacitors controlled by a single shaft.
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31. Glossary Hartley oscillator Oscillator Period
A basic type of oscillator that has a tapped oscillator coil.
Oscillator
An electron tube generator of alternating current voltages.
Period
Time for one complete cycle.
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32. Glossary Pierce oscillator Piezoelectric effect
Type of Colpitts oscillator in which a crystal is used in place of the inductor in the tank circuit.
Piezoelectric effect
Property in which certain crystalline substances change shape when an emf is impressed upon a crystal. The action is also reversible.
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33. Glossary Positive feedback Power oscillator
Energy fed back to the tuned circuit. Also called regenerative feedback.
Power oscillator
Oscillator that uses the collector load of the transistors as primary and the ac output at the secondary.
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34. Glossary Regenerative feedback Series fed oscillator
Feedback in phase with the input signal so it adds to the input.
Series fed oscillator
Oscillator in which the inductor is in series with the transistor collector circuit.
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35. Glossary Shunt fed oscillator Signal generator
Oscillator whose dc path for the emitter-collector is not through the inductor, causing  two current components to separate and take parallel paths.
Signal generator
An electronic oscillator that generates various signals for testing.
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