A duplexer is a device that allows bi-directional communication over a single channel. In radio communications systems, it isolates the receiver from the transmitter while permitting them to share a common antenna. Most radio repeater systems include a duplexer.
Duplexers must:
Be designed for operation in the frequency band used by the receiver and transmitter and must be capable of handling the output power of the transmitter.
Provide adequate rejection of transmitter noise occurring at the receive frequency, and must be designed to operate at, or less than, the frequency separation between the transmitter and receiver.
Supply enough isolation to prevent receiver desensitization.
Diplexer vs Duplexer. What is the difference?
A diplexer is a passive device that combines two inputs into a common output. The signals on inputs 1 and 2 occupy different frequency bands. Consequently, the signals on inputs 1 and 2 can coexist on the output without interfering with each other. It is also known as a cross band combiner. A duplexer is a passive device that allows bi-directional (duplex) communication of transmit and receive frequencies within the same band over a single path.
Types of Duplexers
There are two basic types of duplexers: Band Pass and Band Reject.
Bandpass Duplexers:
Generally will have higher branch loss than pass-reject type, 1.5 dB per branch or higher being expected
Far superior for dense site use. The multiple cavity strings provide added selectivity for the receiver and a high order of spurious and harmonic rejection for the transmitter
Requires larger, higher “Q” cavities, and more of them, resulting in higher cost and need for greater site space occupancy
Through use of correct branch cable lengths and careful loop coupling adjustments, this duplexer type can be tuned for a broad “nose” response to accommodate multi-frequency transmitters and receivers
Impractical for closely spaced TX-RX pairs, compared to pass/notch types. Higher costs than pass notch types due to requiring larger cavities
Band Reject Duplexers (a.k.a. Pass/Notch):
Lower insertion loss than band pass types for same TX-RX spacings
Since pass band is broad, little help is provided in receiver front end selectivity except for the transmit carrier notch; this can be a real problem when placed at high density sites
Can use smaller volume cavities for a given TX-RX spacing, saving space
Lower cost to manufacture; savings in materials and labor
High and Low Band Duplexers
To choose the right duplexer for your application, please browse the full Tessco duplexer offering.