# E7H01 - What are three common oscillator circuits?

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**Category:** Extra Questions\
**Created:** [January 2, 2026, 7:53pm UTC](https://forum.openhamprep.com/t/e7h01-what-are-three-common-oscillator-circuits/1423 "2026-01-02T19:53:28Z")\
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**Post date:** [January 2, 2026, 7:53pm UTC](https://forum.openhamprep.com/t/e7h01-what-are-three-common-oscillator-circuits/1423/1 "2026-01-02T19:53:28Z")

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## Question

What are three common oscillator circuits?

## Answer Options

- **A)** Taft, Pierce, and negative feedback
- **B)** Pierce, Fenner, and Beane
- **C)** Taft, Hartley, and Pierce
- **D)** Colpitts, Hartley, and Pierce

**Correct Answer: D**

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## Explanation

An oscillator is an electronic circuit that generates a repetitive electronic signal (usually a sine wave or square wave) without the need for an external input signal. The circuit relies on an amplifier combined with a positive feedback loop and a frequency-determining (resonant) element to sustain the oscillation.

Three common oscillator circuits named after their inventors and widely used in radio are the **Colpitts, Hartley, and Pierce** circuits. The Colpitts and Hartley oscillators use an \text{LC} tank circuit (L and C) in the feedback loop for frequency determination, while the Pierce oscillator uses a quartz crystal as the high-Q resonant element for maximum frequency stability.

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