A passive Duplexer is used to share the VHF antenna between the OWL VHF radio and the AIS. Port 1 of the Duplexer has a notch filter that attenuates the frequency used by Port 2. Similarly, Port 2 attenuates the frequencies used by Port 1. Both radios can transmit whenever they want, and they won't hear each other, but everything will be sent out on the antenna. The advantages of having a Duplexer rather than an active splitter, is that the Duplexer is completely passive and consists of mechanical filters. The filters are tuned to specific frequencies, so the radios cannot change their frequency.

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