What is a duplexer and why is it critical in repeater deployments?

• A. Filters only the transmit path
• B. Converts between digital and analog
• C. Allows simultaneous transmit and receive on different frequencies using isolation to prevent transmitter leakage into the receiver
• D. Attenuates the received signal

Answer: (C)

A duplexer is the device that lets you transmit and receive at the same time on different frequencies while sharing the same antenna. It does this by using tuned filters and a switching network to route the transmit signal toward the antenna while blocking or greatly reducing that strong signal from leaking into the receiver. This isolation protects the receiver from desensing or damage and lets the repeater hear incoming signals even while it’s transmitting.

That’s why the best description is that a duplexer enables simultaneous transmit and receive on different frequencies using isolation to prevent transmitter leakage into the receiver. It’s not just filtering the transmit path, not a digital-to-analog converter, and not simply attenuating the received signal.