*Question E7H05:
How is positive feedback supplied in a Pierce oscillator?*  

*Correct Answer is  D: Through a quartz crystal*  

### AI Response: (may contain errors)  

In a Pierce oscillator, positive feedback is supplied through a quartz crystal. Here's a breakdown of why this is the correct answer and why the other options are not suitable.

### Correct Answer: D - Through a quartz crystal

- **Explanation**: 
  - A Pierce oscillator uses a quartz crystal to provide the necessary frequency stability and positive feedback. The crystal acts as a frequency-selective element, allowing the oscillator to maintain a stable oscillation at its resonant frequency. The feedback is taken from the output of the amplifier and fed back to the input through the crystal, ensuring that the oscillation is sustained.

### Why the Other Choices are Incorrect:

- **A: Through a tapped coil**  
  - **Explanation**: Tapped coils are typically used in other types of oscillators (like LC oscillators) to provide feedback, but they do not provide the frequency stability and precision that a quartz crystal does. In a Pierce oscillator, the feedback is specifically designed to be frequency-selective, which a tapped coil cannot achieve effectively.

- **B: Through link coupling**  
  - **Explanation**: Link coupling refers to a method of transferring energy between circuits, often seen in transformers or inductively coupled circuits. While it can provide feedback in some oscillator designs, it is not the mechanism used in a Pierce oscillator, which relies on the crystal for feedback.

- **C: Through a neutralizing capacitor**  
  - **Explanation**: A neutralizing capacitor is used to cancel unwanted feedback or oscillations in certain amplifier circuits, particularly in RF amplifiers. It does not provide positive feedback; rather, it is used to stabilize the circuit by eliminating feedback that could lead to instability.

### Summary

In summary, the Pierce oscillator's reliance on a quartz crystal for positive feedback is what distinguishes it from other oscillator types. The crystal ensures stable oscillation at a specific frequency, which is crucial for many applications in amateur radio and electronics.