Diplexer
Encyclopedia
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 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.
The chief advantage of a diplexer is that it allows two different devices to share a common communications channel. Typically the shared channel is a long piece of coaxial cable. Rather than run two separate cables, a single cable with diplexers at each end is used. The plan is economical if the diplexers cost less than running the 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.
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.
and keep reflected power (VSWR) to a minimum for each input transmitter and frequency
. While diplexers can combine a relatively wide bandwidth, the major limitation comes with the antenna itself, which must be sufficiently wideband
to accept all of the signals being passed through it, and transfer them to the air efficiently
.
One of the most massive diplexers in use is atop the Empire State Building
in New York, where over a dozen FM
radio station
s transmit through one four-panel antenna. Another such setup is on a tower in Miami Gardens, serving the Miami and Fort Lauderdale media market
.
Many other large UHF-/VHF-transmitters use diplexers. The number of transmitters which can share an antenna is restricted by the spacing of their frequency bands. Transmitters whose frequencies are too close together cannot be combined successfully by a diplexer.
Diplexers are also used at medium wave broadcasting stations. However their use is not that common in this frequency range because the corresponding wavelength varies much more across the medium wave band than across the FM band and so it is more practicable to use a separate antenna for each frequency: medium wave transmission sites usually broadcast only on one to four frequencies, while FM-broadcasting sites often uses four and more frequencies.
Diplexers may be used as a back-up device. An example is maintenance work at one antenna of a medium wave transmission site that has two antennas transmitting on two frequencies. Then the other antenna can be used for broadcasting both channels. If it is not possible to build a second antenna for the second transmitter due to space constraints, then the diplexer is used permanently.
At long wave broadcasting sites diplexers are normally not used since these stations usually broadcast on only one frequency. A realization of diplexers for long wave broadcasting stations may be difficult, as the ratio of bandwidth (9 kHz) to transmission frequency is high.
Diplexers are not used at VLF transmitters. In this frequency range their realization is very difficult because of the very high voltages that occur in the huge tuned loading coils that are used in the antenna feed.
Diplexers are also used for non-broadcast
applications such as amateur radio
.
satellite TV
signals from the dish
to the receiver
to piggyback
on one regular coaxial cable
, along with lower-frequency signals from an outdoor terrestrial TV antenna for local channels. This is useful in homes which are already pre-wired, because it eliminates the need to install extra cables. However, the pre-wired cables must be the higher-quality RG-6
. The less-expensive RG-59
will not pass the higher frequency band (usually 950 to 1450 MHz) output by the satellite TV LNB
.
In this case, one diplexer joins the two signals together. Another diplexer then separates the signals to the receiver of the TV set and the IRD
of the DBS set-top box
. More complex systems have a distribution amplifier
, which allows each IRD to access multiple LNBs with different antenna polarizations. These usually have an antenna input and a diplexer, so that the antenna signal is also distributed along with the satellite.
Diplexers are also commonly used to combine UHF TV and VHF TV and FM signals onto one downlead, which can then be split back into its component parts as required.
A DSL filter
may also be considered a diplexer, because it splits baseband
telephone
audio and modulate
d data
. However, the term is usually reserved for radio frequencies; and also such a filter
may only remove the DSL from the phone side, but not the phone from the DSL side.
Electronic component
An electronic component is a basic electronic element and may be available in a discrete form having two or more electrical terminals . These are intended to be connected together, usually by soldering to a printed circuit board, in order to create an electronic circuit with a particular function...
that implements frequency domain multiplexing
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
. 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 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 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.
Common uses
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.
A diplexer may be used as a form of duplexer, which is a device to enable bi-directional (duplex
Duplex (telecommunications)
A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions. The term multiplexing is used when describing communication between more than two parties or devices....
) 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.
Industrial applications
Diplexing is used to prevent intermodulationIntermodulation
Intermodulation or intermodulation distortion is the amplitude modulation of signals containing two or more different frequencies in a system with nonlinearities...
and keep reflected power (VSWR) to a minimum for each input transmitter and frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
. While diplexers can combine a relatively wide bandwidth, the major limitation comes with the antenna itself, which must be sufficiently wideband
Wideband
In communications, wideband is a relative term used to describe a wide range of frequencies in a spectrum. A system is typically described as wideband if the message bandwidth significantly exceeds the channel's coherence bandwidth....
to accept all of the signals being passed through it, and transfer them to the air efficiently
Energy conversion efficiency
Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat.-Overview:...
.
One of the most massive diplexers in use is atop the Empire State Building
Empire State Building
The Empire State Building is a 102-story landmark skyscraper and American cultural icon in New York City at the intersection of Fifth Avenue and West 34th Street. It has a roof height of 1,250 feet , and with its antenna spire included, it stands a total of 1,454 ft high. Its name is derived...
in New York, where over a dozen FM
FM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
radio station
Radio station
Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both...
s transmit through one four-panel antenna. Another such setup is on a tower in Miami Gardens, serving the Miami and Fort Lauderdale media market
Media market
A media market, broadcast market, media region, designated market area , Television Market Area , or simply market is a region where the population can receive the same television and radio station offerings, and may also include other types of media including newspapers and Internet content...
.
Many other large UHF-/VHF-transmitters use diplexers. The number of transmitters which can share an antenna is restricted by the spacing of their frequency bands. Transmitters whose frequencies are too close together cannot be combined successfully by a diplexer.
Diplexers are also used at medium wave broadcasting stations. However their use is not that common in this frequency range because the corresponding wavelength varies much more across the medium wave band than across the FM band and so it is more practicable to use a separate antenna for each frequency: medium wave transmission sites usually broadcast only on one to four frequencies, while FM-broadcasting sites often uses four and more frequencies.
Diplexers may be used as a back-up device. An example is maintenance work at one antenna of a medium wave transmission site that has two antennas transmitting on two frequencies. Then the other antenna can be used for broadcasting both channels. If it is not possible to build a second antenna for the second transmitter due to space constraints, then the diplexer is used permanently.
At long wave broadcasting sites diplexers are normally not used since these stations usually broadcast on only one frequency. A realization of diplexers for long wave broadcasting stations may be difficult, as the ratio of bandwidth (9 kHz) to transmission frequency is high.
Diplexers are not used at VLF transmitters. In this frequency range their realization is very difficult because of the very high voltages that occur in the huge tuned loading coils that are used in the antenna feed.
Diplexers are also used for non-broadcast
Broadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
applications such as amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
.
Residential
Small diplexers are also used in the home, allowing direct broadcastDirect broadcast satellite
Direct broadcast satellite is a term used to refer to satellite television broadcasts intended for home reception.A designation broader than DBS would be direct-to-home signals, or DTH. This has initially distinguished the transmissions directly intended for home viewers from cable television...
satellite TV
Satellite television
Satellite television is television programming delivered by the means of communications satellite and received by an outdoor antenna, usually a parabolic mirror generally referred to as a satellite dish, and as far as household usage is concerned, a satellite receiver either in the form of an...
signals from the dish
Satellite dish
A satellite dish is a dish-shaped type of parabolic antenna designed to receive microwaves from communications satellites, which transmit data transmissions or broadcasts, such as satellite television.-Principle of operation:...
to the receiver
Integrated receiver/decoder
An integrated receiver/decoder is an electronic device used to pick-up a radio-frequency signal and convert digital information transmitted in it.-Consumer IRDs:...
to piggyback
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
on one regular coaxial cable
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
, along with lower-frequency signals from an outdoor terrestrial TV antenna for local channels. This is useful in homes which are already pre-wired, because it eliminates the need to install extra cables. However, the pre-wired cables must be the higher-quality RG-6
RG-6
RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. The term "RG-6" itself is quite generic and refers to a wide variety of cable designs, which differ from one another in shielding characteristics, center conductor composition, and...
. The less-expensive RG-59
RG-59
RG-59/U is a specific type of coaxial cable, often used for low-power video and RF signal connections. The cable has a characteristic impedance of 75 ohms. The 75 ohm impedance matches a dipole antenna in free space. "RG" was originally a unit indicator for bulk radio frequency cable in the...
will not pass the higher frequency band (usually 950 to 1450 MHz) output by the satellite TV LNB
Low-noise block converter
A low-noise block downconverter is the receiving device of a parabolic satellite dish antenna of the type commonly used for satellite TV reception...
.
In this case, one diplexer joins the two signals together. Another diplexer then separates the signals to the receiver of the TV set and the IRD
Integrated receiver/decoder
An integrated receiver/decoder is an electronic device used to pick-up a radio-frequency signal and convert digital information transmitted in it.-Consumer IRDs:...
of the DBS set-top box
Set-top box
A set-top box or set-top unit is an information appliance device that generally contains a tuner and connects to a television set and an external source of signal, turning the signal into content which is then displayed on the television screen or other display device.-History:Before the...
. More complex systems have a distribution amplifier
Distribution amplifier
In electronics, a distribution amplifier or simply distribution amp, is a device that accepts a single input signal and provides this same signal to multiple isolated outputs....
, which allows each IRD to access multiple LNBs with different antenna polarizations. These usually have an antenna input and a diplexer, so that the antenna signal is also distributed along with the satellite.
Diplexers are also commonly used to combine UHF TV and VHF TV and FM signals onto one downlead, which can then be split back into its component parts as required.
A DSL filter
DSL filter
A DSL filter is an analog low-pass filter installed between analog devices and a plain old telephone service telephone line, in order to prevent interference between such devices and a digital subscriber line service operating on the same line...
may also be considered a diplexer, because it splits baseband
Baseband
In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...
telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
audio and modulate
Modulate
Modulate is Bob Mould's fifth solo album, released in 2002. Although a few tracks on his previous release, The Last Dog and Pony Show, had featured tape loops and samples, Mould shocked his fans with such a dramatic embrace of electronica...
d data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
. However, the term is usually reserved for radio frequencies; and also such a filter
Electronic filter
Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both...
may only remove the DSL from the phone side, but not the phone from the DSL side.
See also
- Duplexer
- Power dividers and directional couplersPower dividers and directional couplersPower dividers and directional couplers are passive devices used in the field of radio technology. They couple a defined amount of the electromagnetic power in a transmission line to another port where it can be used in another circuit...
- MultiplexingMultiplexingThe multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
- Bias teeBias teeA bias tee is a three port network used for setting the DC bias point of some electronic components without disturbing other components. The bias tee is a diplexer. The low frequency port is used to set the bias; the high frequency port passes the radio frequency signals but blocks the biasing...