Editing Duplexer

{{Short description|Device that allows bi-directional communication over a single path}}
{{Distinguish|Diplexer}}
{{other uses|Duplex (disambiguation)|Duplex printing}}

A '''duplexer''' is an electronic device that allows bi-directional ([[duplex (telecommunications)|duplex]]) communication over a single path. In [[radar]] and radio communications systems, it isolates the [[receiver (radio)|receiver]] from the [[transmitter]] while permitting them to share a common [[antenna (electronics)|antenna]]. Most [[radio repeater]] systems include a duplexer. Duplexers can be based on frequency (often a [[waveguide filter]]), polarization (such as an [[orthomode transducer]]), or timing (as is typical in radar).<ref>{{cite book |title=Radar for Meteorologists |author= Rinehart, Ronald E. |publisher= University of North Dakota |year=1991}} Radar engineers have added the automatic
switch (also called a duplexer) in the ... As soon as the transmitter stops sending a signal, the
duplexer switches so that the receiver is now connected to the antenna.</ref>

==Types==

===Transmit-receive switch===
[[Image:Bsp_Duplex-eng.svg|thumb|TR duplex switching]]
In radar, a transmit/receive (TR) switch alternately connects the transmitter and receiver to a shared antenna. In the simplest arrangement, the switch consists of a [[Sutton tube#Soft Sutton tube|gas-discharge tube]] across the input terminals of the receiver. When the transmitter is active, the resulting high voltage causes the tube to conduct, shorting together the receiver terminals to protect it, while its complementary, the anti-transmit/receive (ATR) switch, is a similar discharge tube which decouples the transmitter from the antenna while not operating, to prevent it from wasting received energy.

===Circulator===
{{Main|Circulator}}

===Hybrid===
A [[hybrid coil|hybrid]], such as a [[magic T]], may be used as a duplexer by terminating the fourth port in a [[electrical termination|matched load]].<ref>{{cite book
 |last1=Sisodia
 |last2=Gupta
 |date=2007
 |title=Microwaves: Introduction To Circuits,Devices And Antennas
 |url= https://books.google.com/books?id=iEvgmwH1esgC&pg=SA4-PA40
 |location=New Delhi
 |publisher=New Age International
 |page=4.40
 |isbn=9788122413380
}}</ref>
This arrangement suffers from the disadvantage that half of the transmitter power is lost in the matched load, while [[thermal noise]] in the load is delivered to the receiver.

===Orthomode transducer===
{{Main|Orthomode transducer}}

===Frequency domain===
[[Image:Repeater duplexer.png|right|190px]]

In radio communications (as opposed to radar), the transmitted and received signals can occupy different frequency bands, and so may be separated by frequency-selective filters. These are effectively a higher-performance version of a [[diplexer]], typically with a narrow split between the two frequencies in question (typically around 2%-5% for a commercial two-way radio system).

With a duplexer the high- and low-frequency signals are traveling in opposite directions at the shared [[Port (circuit theory)|port]] of the duplexer.

Modern duplexers often use nearby frequency bands, so the frequency separation between the two ports is also much less. For example, the transition between the uplink and downlink bands in the [[GSM frequency bands]] may be about one percent (915&nbsp;MHz to 925&nbsp;MHz). Significant attenuation (isolation) is needed to prevent the transmitter's output from overloading the receiver's input, so such duplexers employ multi-pole filters. Duplexers are commonly made for use on the 30-50 MHz ("low band"), 136-174 MHz ("high band"), 380-520 MHz ("UHF"), plus the  790–862 MHz ("800"), 896-960 MHz ("900") and 1215-1300 MHz ("1200") bands.

There are two predominant types of duplexer in use - "notch duplexers", which exhibit sharp notches at the "unwanted" frequencies and only pass through a narrow band of wanted frequencies and "bandpass duplexers", which have wide-pass frequency ranges and high out-of-band attenuation.

On shared-antenna sites, the bandpass duplexer variety is greatly preferred because this virtually eliminates interference between transmitters and receivers by removing out-of-band transmit emissions and considerably improving the selectivity of receivers. Most professionally engineered sites ban the use of notch duplexers and insist on bandpass duplexers for this reason.

[[File:Kathrein-weiche.jpg|thumb|350px|Commercial 19" rack mount antenna filter<br>Isolation typical >75 dB <br> Insertion Loss typical < 1.0 dB]]

''Note 1:''  A duplexer must be designed for operation in the [[frequency]] [[band (radio)|band]] used by the receiver and transmitter, and must be capable of handling the output [[Power (physics)|power]] of the transmitter.

''Note 2:''  A duplexer must 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.

''Note 3:''  A duplexer must provide sufficient isolation to prevent receiver desensitization.

Source: from [[Federal Standard 1037C]]

==History==
The first duplexers were invented for use on the [[electric telegraph]] and were known as ''duplex'' rather than ''duplexer''. They were an early form of the [[hybrid coil]]. The telegraph companies were keen to have such a device since the ability to have simultaneous traffic in both directions had the potential to save the cost of thousands of miles of telegraph wire. The first of these devices was designed in 1853 by [[Julius Wilhelm Gintl]] of the Austrian State Telegraph. Gintl's design was not very successful. Further attempts were made by Carl Frischen of Hanover with an artificial line to balance the real line as well as by [[Siemens & Halske]], who bought and modified Frischen's design. The first truly successful duplex was designed by [[Joseph Barker Stearns]] of Boston in 1872. This was further developed into the [[quadruplex telegraph]] by [[Thomas Edison]]. The device is estimated to have saved [[Western Union]] $500,000 per year in construction of new telegraph lines.<ref>Tom Standage, ''The Victorian Internet'', ch. 11, Walker & Company, 2007 {{ISBN|978-0-802-71879-2}}.</ref><ref>George Bartlett Prescott, ''Electricity and the Electric Telegraph'', pp. 792-793, New York: D. Appleton, 1877 {{oclc|999414808}}</ref>

The first duplexers for radar, sometimes referred to as Transmit/Receive Switches, were invented by [[Robert Morris Page]] and [[Leo C. Young]] of the [[United States Naval Research Laboratory]] in July 1936.<ref>Page, Robert Morris; ''The Origin of Radar'', Doubleday & Company, 1962, pp. 118-125</ref>

==References==
{{reflist}}

[[Category:Broadcast engineering]]
[[Category:Radio electronics]]
[[Category:Electronic circuits]]
[[Category:Telegraphy]]

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