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

To stop intermodulation interference at a repeater site, you must prevent outside RF signals from traveling backward into the transmitter's final amplifier. This is achieved using a device called a circulator. A circulator is a passive, multi-port ferrite device that acts like a one-way valve for RF energy. When installed at the transmitter's output and properly terminated with a dummy load on its third port, it allows the transmitter's outbound signal to pass freely to the antenna. However, any incoming signals from nearby transmitters are routed into the dummy load, destroying them as heat before they can reach the final amplifier and mix. While band-pass filters (like cavities) are used extensively at repeater sites to isolate frequencies, a circulator is specifically designed to provide this highly effective directional isolation at the transmitter output. Using Class C or D amplifiers would actually worsen intermodulation because they are highly non-linear.