*Question E7H02:
What is a microphonic?*  

*Correct Answer is  C: Changes in oscillator frequency caused by mechanical vibration*  

### AI Response: (may contain errors)  

A microphonic effect refers to changes in oscillator frequency caused by mechanical vibration. This is the correct answer (Choice C) because when an oscillator is subjected to physical vibrations, it can cause the components within the oscillator circuit to move slightly. This movement can change the capacitance or inductance in the circuit, leading to a shift in the oscillator's frequency.

### Explanation of Choices:

- **Choice A: An IC used for amplifying microphone signals**  
  This is incorrect because a microphonic is not a type of integrated circuit (IC). Instead, it refers to a phenomenon affecting oscillators, not a device used for amplification.

- **Choice B: Distortion caused by RF pickup on the microphone cable**  
  This is incorrect because RF pickup on a microphone cable is a different issue, often related to shielding and grounding problems, not related to the microphonic effect.

- **Choice C: Changes in oscillator frequency caused by mechanical vibration**  
  This is correct. The term "microphonic" describes the sensitivity of electronic components, especially oscillators, to mechanical vibrations, which can cause frequency instability.

- **Choice D: Excess loading of the microphone by an oscillator**  
  This is incorrect because excess loading refers to impedance mismatches or overloading issues, not related to the microphonic effect.

### Key Points:

- **Microphonic Effect**: Primarily affects oscillators and can lead to frequency instability.
- **Prevention**: To minimize microphonic effects, components can be mechanically isolated or dampened to reduce vibrations.

Understanding the microphonic effect is important for ensuring stable oscillator performance in radio equipment.