*Question E7E03:
What is a frequency discriminator?*  

*Correct Answer is  D: A circuit for detecting FM signals*  

### AI Response: (may contain errors)  

A frequency discriminator is a circuit used to detect frequency-modulated (FM) signals. Here's why the correct answer is correct and why the other choices are incorrect:

1. **Correct Answer: D - A circuit for detecting FM signals**
   - A frequency discriminator is specifically designed to convert frequency variations in an FM signal into amplitude variations. This process is essential for demodulating FM signals, allowing the original audio or data signal to be recovered from the modulated carrier.

2. **Why the other choices are incorrect:**
   - **A: An FM generator circuit**
     - An FM generator circuit is used to create FM signals, not to detect them. It modulates a carrier frequency with an input signal, producing an FM output.
   - **B: A circuit for filtering closely adjacent signals**
     - This describes a filter circuit, which is used to separate or reject unwanted signals that are close in frequency to the desired signal. It does not perform FM detection.
   - **C: An automatic band-switching circuit**
     - An automatic band-switching circuit is used in receivers or transmitters to switch between different frequency bands. It is unrelated to FM signal detection.

In summary, a frequency discriminator is crucial for FM demodulation, converting frequency changes into amplitude changes to retrieve the original information from an FM signal.