*Question E4D04:
Which of the following is used to reduce or eliminate intermodulation interference in a repeater caused by a nearby transmitter?*  

*Correct Answer is  B: A properly terminated circulator at the output of the repeater’s transmitter*  

### AI Response: (may contain errors)  

To address intermodulation interference in a repeater caused by a nearby transmitter, a properly terminated circulator at the output of the repeater’s transmitter is used. Here's why:

1. **Correct Answer: B - A properly terminated circulator at the output of the repeater’s transmitter**
   - A circulator is a passive device that routes signals from one port to the next in a sequential manner. When properly terminated, it helps prevent signals from reflecting back into the transmitter, which can cause intermodulation distortion. This is particularly useful in repeater systems where multiple signals are present, as it helps isolate the transmitter from the receiver and other nearby transmitters.

2. **Why the Other Choices are Incorrect:**
   - **A: A band-pass filter in the feed line between the transmitter and receiver**
     - While a band-pass filter can help reduce unwanted signals by allowing only a specific range of frequencies to pass, it does not specifically address intermodulation interference caused by nearby transmitters. It is more effective for filtering out-of-band signals rather than isolating components within the system.
   
   - **C: Utilizing a Class C final amplifier**
     - Class C amplifiers are efficient for RF amplification but are not linear. They can actually contribute to intermodulation distortion because they amplify signals in a non-linear manner, which can mix signals and create unwanted intermodulation products.
   
   - **D: Utilizing a Class D final amplifier**
     - Class D amplifiers are typically used for audio applications and are not suitable for RF applications like repeaters. They operate by switching and are not designed to handle RF signals, thus not addressing intermodulation issues in RF systems.

In summary, a properly terminated circulator is effective in reducing intermodulation interference by isolating the transmitter from other components and preventing signal reflections, which is crucial in maintaining the integrity of signals in a repeater system.