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A diplexer is a passive device that implements frequency-domain multiplexing. Two ports (e.g., L and H) are multiplexed onto a third port (e.g., S). The signals on ports L and H occupy disjoint frequency bands. Consequently, the signals on L and H can coexist on port S without interfering with each other. Typically, the signal on port L will occupy a single low frequency band and the signal on port H will occupy a higher frequency band. In that situation, the diplexer consists of a lowpass filter connecting ports L and S and high pass filter connecting ports H and S. Ideally, all the signal power on port L is transferred to the S port and vice versa. All the signal power on port H is transferred to port S and vice versa. Ideally, the separation of the signals is complete. None of the low band signal is transferred from the S port to the H port. In the real world, some power will be lost, and some signal power will leak to the wrong port. The diplexer, being a passive device, is reciprocal: the device itself doesn't have a notion of input or output. The diplexer is a different device than a passive combiner or splitter. The ports of a diplexer are frequency selective; the ports of a combiner are not. There is also a power "loss" difference - a combiner takes all the power delivered to the S port and equally divides it between the A and B ports. A diplexer does not. A diplexer frequency multiplexes two ports onto one port, but more than two ports may be multiplexed. A three-port to one-port multiplexer is known as a triplexer, and a four-port to one-port multiplexer is a quadplexer or quadruplexer. ==Common uses== A diplexer allows two different devices to share a common communications channel. Typically, the channel is a long coaxial cable, and a diplexer is often used at both ends of the coaxial cable. The plan is feasible if the two devices operate on different frequencies. The plan is economical if the diplexers cost less than running a second cable. Diplexers might be used to connect two receivers inside a building to two antennas that are some distance away using a single cable. Alternatively, two transmitters might connect to two antennas. Diplexers are typically used with radio receivers or transmitters on different, widely separated, frequency bands. A single city radio tower might have a police department antenna on 460 MHz and a fire department antenna on 156 MHz. A diplexer at the top combines the two antenna signals to the single coaxial feedline, and a second identical diplexer inside the building separates the feedline signals to the two dispatch radios. Some diplexers support as many as four antennas or radios that work on different radio bands. A diplexer may be used as a form of duplexer, which is a device to enable bi-directional (duplex) communication over a single path. In this usage, the high and low frequency signals are travelling in opposite directions at the shared port of the diplexer. 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 1 percent (915 MHz to 925 MHz). Significant attenuation (isolation) is needed to prevent the transmitter's output from overloading the receiver's input, so such duplexers will 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Diplexer」の詳細全文を読む スポンサード リンク
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