Question
Which of the following is used to reduce or eliminate intermodulation interference in a repeater caused by a nearby transmitter?
Answer Options
- A) A band-pass filter in the feed line between the transmitter and receiver
- B) A properly terminated circulator at the output of the repeater’s transmitter
- C) Utilizing a Class C final amplifier
- D) Utilizing a Class D final amplifier
Correct Answer: B
Explanation
Intermodulation (IM) interference, caused by the outputs of multiple transmitters mixing in a non-linear junction, can occur either externally (in rusty fences or tower joints) or internally (in the final amplifier of one of the transmitters). To combat internal IM, the repeater transmitter must be protected from external RF energy leaking into its output stage.
This isolation and protection are achieved by installing a properly terminated circulator at the output of the repeater’s transmitter. A circulator is a non-reciprocal device that directs power from the transmitter toward the antenna while simultaneously shunting any external RF energy leaking back into the output stage (which would cause IM) into a dummy load (the termination), preventing it from causing the IM product.
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