Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables , or in more recent systems, light pulses through fibre-optic cables . This contrasts with broadcast television , in which the television signal is transmitted over-the-air by radio waves and received by a television antenna , or satellite television , in which the television signal is transmitted over-the-air by radio waves from a communications satellite and received by a satellite dish on the roof. FM radio programming, high-speed Internet , telephone services , and similar non-television services may also be provided through these cables. Analog television was standard in the 20th century, but since the 2000s, cable systems have been upgraded to digital cable operation.
90-786: Destiny Cable (formerly Global Destiny Cable and stylized as DESTINY CABLE ) was a direct-to-home cable television subscription service based in Quezon City . Destiny Cable was the 2nd largest cable TV provider in the Philippines. It was owned by Sky Cable Corporation . On January 1, 1995, the Philippines’ commission attached to the Department of Transportation and Communications , the National Telecommunications Commission (NTC) granted
180-621: A certificate of public convenience and necessity with provisional authority to install, operate and maintain telecommunications, broadcast and cable antenna television services to Destiny Cable Inc was officially launched on January 16, 1995. and allowed to provide cable television services to Metro Manila and nearby municipalities, cities and provinces. Destiny Cable Inc. embarked on marketing promotion through Solid Group Inc. by offering bundled services. On November 17, 2000, however, Global Cable, Inc. (GCI) and Destiny Cable, Inc. (DCI) announced that both companies had entered an agreement on merging
270-506: A coupled-line hybrid. The Wilkinson power divider consists of two parallel uncoupled λ/4 transmission lines. The input is fed to both lines in parallel and the outputs are terminated with twice the system impedance bridged between them. The design can be realised in planar format but it has a more natural implementation in coax – in planar, the two lines have to be kept apart so that they do not couple but have to be brought together at their outputs so they can be terminated whereas in coax
360-405: A dedicated analog circuit-switched service. Other advantages include better voice quality and integration to a Voice over Internet Protocol (VoIP) network providing cheap or unlimited nationwide and international calling. In many cases, digital cable telephone service is separate from cable modem service being offered by many cable companies and does not rely on Internet Protocol (IP) traffic or
450-711: A few authors go so far as to define it as a positive quantity. Coupling is not constant, but varies with frequency. While different designs may reduce the variance, a perfectly flat coupler theoretically cannot be built. Directional couplers are specified in terms of the coupling accuracy at the frequency band center. The main line insertion loss from port 1 to port 2 (P 1 – P 2 ) is: Insertion loss: L i 2 , 1 = − 10 log ( P 2 P 1 ) d B {\displaystyle L_{i2,1}=-10\log {\left({\frac {P_{2}}{P_{1}}}\right)}\quad {\rm {dB}}} Part of this loss
540-436: A given location, cable distribution lines must be available on the local utility poles or underground utility lines. Coaxial cable brings the signal to the customer's building through a service drop , an overhead or underground cable. If the subscriber's building does not have a cable service drop, the cable company will install one. The standard cable used in the U.S. is RG-6 , which has a 75 ohm impedance , and connects with
630-543: A high elevation. At the outset, cable systems only served smaller communities without television stations of their own, and which could not easily receive signals from stations in cities because of distance or hilly terrain. In Canada, however, communities with their own signals were fertile cable markets, as viewers wanted to receive American signals. Rarely, as in the college town of Alfred, New York , U.S. cable systems retransmitted Canadian channels. Although early ( VHF ) television receivers could receive 12 channels (2–13),
720-466: A higher rate. At the local headend, the feed signals from the individual television channels are received by dish antennas from communication satellites . Additional local channels, such as local broadcast television stations, educational channels from local colleges, and community access channels devoted to local governments ( PEG channels) are usually included on the cable service. Commercial advertisements for local business are also inserted in
810-449: A hybrid coupler should be 0°, 90°, or 180° depending on the type used. However, like amplitude balance, the phase difference is sensitive to the input frequency and typically will vary a few degrees. The most common form of directional coupler is a pair of coupled transmission lines. They can be realised in a number of technologies including coaxial and the planar technologies ( stripline and microstrip ). An implementation in stripline
900-405: A local VHF television station broadcast. Local broadcast channels were not usable for signals deemed to be a priority, but technology allowed low-priority signals to be placed on such channels by synchronizing their blanking intervals . TVs were unable to reconcile these blanking intervals and the slight changes due to travel through a medium, causing ghosting . The bandwidth of the amplifiers also
990-463: A microwave-based system, may be used instead. Coaxial cables are capable of bi-directional carriage of signals as well as the transmission of large amounts of data . Cable television signals use only a portion of the bandwidth available over coaxial lines. This leaves plenty of space available for other digital services such as cable internet , cable telephony and wireless services, using both unlicensed and licensed spectra. Broadband internet access
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#17327796332331080-419: A multi-section filter design in the same way as the multiple sections of a coupled-line coupler except that here the coupling of each section is controlled with the impedance of the branch lines. The main and coupled line are 2 {\displaystyle \scriptstyle {\sqrt {2}}} of the system impedance. The more sections there are in the coupler, the higher is the ratio of impedances of
1170-564: A rarity, found in an ever-dwindling number of markets. Analog television sets are accommodated, their tuners mostly obsolete and dependent entirely on the set-top box. Cable television is mostly available in North America , Europe , Australia , Asia and South America . Cable television has had little success in Africa , as it is not cost-effective to lay cables in sparsely populated areas. Multichannel multipoint distribution service ,
1260-455: A receiver box. The cable company will provide set-top boxes based on the level of service a customer purchases, from basic set-top boxes with a standard-definition picture connected through the standard coaxial connection on the TV, to high-definition wireless digital video recorder (DVR) receivers connected via HDMI or component . Older analog television sets are cable ready and can receive
1350-414: A scattering matrix that is no longer all-zeroes on the antidiagonal. This terminology defines the power difference in dB between the two output ports of a 3 dB hybrid. In an ideal hybrid circuit, the difference should be 0 dB . However, in a practical device the amplitude balance is frequency dependent and departs from the ideal 0 dB difference. The phase difference between the two output ports of
1440-766: A series of signal amplifiers and line extenders. These devices carry the signal to customers via passive RF devices called taps. The very first cable networks were operated locally, notably in 1936 by Rediffusion in London in the United Kingdom and the same year in Berlin in Germany, notably for the Olympic Games , and from 1948 onwards in the United States and Switzerland. This type of local cable network
1530-417: A special telephone interface at the customer's premises that converts the analog signals from the customer's in-home wiring into a digital signal, which is then sent on the local loop (replacing the analog last mile , or plain old telephone service (POTS) to the company's switching center, where it is connected to the public switched telephone network ( PSTN ). The biggest obstacle to cable telephone service
1620-605: A type F connector . The cable company's portion of the wiring usually ends at a distribution box on the building exterior, and built-in cable wiring in the walls usually distributes the signal to jacks in different rooms to which televisions are connected. Multiple cables to different rooms are split off the incoming cable with a small device called a splitter . There are two standards for cable television; older analog cable, and newer digital cable which can carry data signals used by digital television receivers such as high-definition television (HDTV) equipment. All cable companies in
1710-489: A value in dB from the nominal coupling factor. It can be shown that coupled-line directional couplers have τ {\displaystyle \tau \ } purely real and κ {\displaystyle \kappa \ } purely imaginary at all frequencies. This leads to a simplification of the S-matrix and the result that the coupled port is always in quadrature phase (90°) with
1800-444: A wide bandwidth as coupled lines. This style of coupler is good for implementing in high-power, air dielectric, solid bar formats as the rigid structure is easy to mechanically support. Branch line couplers can be used as crossovers as an alternative to air bridges , which in some applications cause an unacceptable amount of coupling between the lines being crossed. An ideal branch-line crossover theoretically has no coupling between
1890-422: Is achieved over coaxial cable by using cable modems to convert the network data into a type of digital signal that can be transferred over coaxial cable. One problem with some cable systems is the older amplifiers placed along the cable routes are unidirectional thus in order to allow for uploading of data the customer would need to use an analog telephone modem to provide for the upstream connection. This limited
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#17327796332331980-512: Is calculated from the addition of the isolation and (negative) coupling measurements as: Note that if the positive definition of coupling is used, the formula results in: The S-matrix for an ideal (infinite isolation and perfectly matched) symmetrical directional coupler is given by, In general, τ {\displaystyle \tau \ } and κ {\displaystyle \kappa \ } are complex , frequency dependent, numbers. The zeroes on
2070-438: Is called a hybrid coupler . Directional couplers are most frequently constructed from two coupled transmission lines set close enough together such that energy passing through one is coupled to the other. This technique is favoured at the microwave frequencies where transmission line designs are commonly used to implement many circuit elements. However, lumped component devices are also possible at lower frequencies, such as
2160-411: Is defined as: C 3 , 1 = 10 log ( P 3 P 1 ) d B {\displaystyle C_{3,1}=10\log {\left({\frac {P_{3}}{P_{1}}}\right)}\quad {\rm {dB}}} where P 1 is the input power at port 1 and P 3 is the output power from the coupled port (see figure 1). The coupling factor represents
2250-432: Is designed for high power operation (large connectors), while the coupled port may use a small connector, such as an SMA connector . The internal load power rating may also limit operation on the coupled line. Accuracy of coupling factor depends on the dimensional tolerances for the spacing of the two coupled lines. For planar printed technologies this comes down to the resolution of the printing process which determines
2340-481: Is due to some power going to the coupled port and is called coupling loss and is given by: Coupling loss: L c 2 , 1 = − 10 log ( 1 − P 3 P 1 ) d B {\displaystyle L_{c2,1}=-10\log {\left(1-{\frac {P_{3}}{P_{1}}}\right)}\quad {\rm {dB}}} The insertion loss of an ideal directional coupler will consist entirely of
2430-420: Is much wider: for instance a coupler specified as 2–4 GHz might have a main line which could operate at 1–5 GHz . The coupled response is periodic with frequency. For example, a λ/4 coupled-line coupler will have responses at n λ/4 where n is an odd integer. This preferred response gets obvious when a short impulse on the main line is followed through the coupler. When the impulse on the main line reaches
2520-430: Is related to τ {\displaystyle \tau \ } by; Coupling factor is related to κ {\displaystyle \kappa \ } by; Non-zero main diagonal entries are related to return loss , and non-zero antidiagonal entries are related to isolation by similar expressions. Some authors define the port numbers with ports 3 and 4 interchanged. This results in
2610-406: Is shown in figure 4 of a quarter-wavelength (λ/4) directional coupler. The power on the coupled line flows in the opposite direction to the power on the main line, hence the port arrangement is not the same as shown in figure 1, but the numbering remains the same. For this reason it is sometimes called a backward coupler . The main line is the section between ports 1 and 2 and the coupled line
2700-571: Is shown in the graph of figure 3 and the table below. Isolation of a directional coupler can be defined as the difference in signal levels in dB between the input port and the isolated port when the two other ports are terminated by matched loads, or: Isolation: I 4 , 1 = − 10 log ( P 4 P 1 ) d B {\displaystyle I_{4,1}=-10\log {\left({\frac {P_{4}}{P_{1}}}\right)}\quad {\rm {dB}}} Isolation can also be defined between
2790-482: Is the need for nearly 100% reliable service for emergency calls. One of the standards available for digital cable telephony, PacketCable , seems to be the most promising and able to work with the quality of service (QOS) demands of traditional analog plain old telephone service (POTS) service. The biggest advantage to digital cable telephone service is similar to the advantage of digital cable, namely that data can be compressed, resulting in much less bandwidth used than
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2880-415: Is the output power from the coupled port and P 4 is the power output from the isolated port. The directivity should be as high as possible. The directivity is very high at the design frequency and is a more sensitive function of frequency because it depends on the cancellation of two wave components. Waveguide directional couplers will have the best directivity. Directivity is not directly measurable, and
2970-402: Is the section between ports 3 and 4. Since the directional coupler is a linear device, the notations on figure 1 are arbitrary. Any port can be the input, (an example is seen in figure 20) which will result in the directly connected port being the transmitted port, the adjacent port being the coupled port, and the diagonal port being the isolated port. On some directional couplers, the main line
3060-487: Is unavoidable. It is, however, possible with four-ports and this is the fundamental reason why four-port devices are used to implement three-port power dividers: four-port devices can be designed so that power arriving at port 2 is split between port 1 and port 4 (which is terminated with a matching load) and none (in the ideal case) goes to port 3. The term hybrid coupler originally applied to 3 dB coupled-line directional couplers, that is, directional couplers in which
3150-492: Is used for devices with tight coupling (commonly, a power divider will provide half the input power at each of its output ports – a 3 dB divider) and is usually considered a 3-port device. Common properties desired for all directional couplers are wide operational bandwidth , high directivity, and a good impedance match at all ports when the other ports are terminated in matched loads. Some of these, and other, general characteristics are discussed below. The coupling factor
3240-606: Is used in the US for cable television and originally stood for community antenna television , from cable television's origins in 1948; in areas where over-the-air TV reception was limited by distance from transmitters or mountainous terrain, large community antennas were constructed, and cable was run from them to individual homes. In 1968, 6.4% of Americans had cable television. The number increased to 7.5% in 1978. By 1988, 52.8% of all households were using cable. The number further increased to 62.4% in 1994. To receive cable television at
3330-492: The DVB-C , DVB-C2 stream to IP for distribution of TV over IP network in the home. Many cable companies offer internet access through DOCSIS . In the most common system, multiple television channels (as many as 500, although this varies depending on the provider's available channel capacity) are distributed to subscriber residences through a coaxial cable , which comes from a trunkline supported on utility poles originating at
3420-407: The coupling factor in dB marked on it. Directional couplers have four ports . Port 1 is the input port where power is applied. Port 3 is the coupled port where a portion of the power applied to port 1 appears. Port 2 is the transmitted port where the power from port 1 is outputted, less the portion that went to port 3. Directional couplers are frequently symmetrical so there also exists port 4,
3510-616: The high band 7–13 of North American television frequencies . Some operators as in Cornwall, Ontario , used a dual distribution network with Channels 2–13 on each of the two cables. During the 1980s, United States regulations not unlike public, educational, and government access (PEG) created the beginning of cable-originated live television programming. As cable penetration increased, numerous cable-only TV stations were launched, many with their own news bureaus that could provide more immediate and more localized content than that provided by
3600-641: The Internet. Traditional cable television providers and traditional telecommunication companies increasingly compete in providing voice, video and data services to residences. The combination of television, telephone and Internet access is commonly called triple play , regardless of whether CATV or telcos offer it. More than 400,000 television service subscribers. Power dividers and directional couplers Power dividers (also power splitters and, when used in reverse, power combiners ) and directional couplers are passive devices used mostly in
3690-485: The United States have switched to or are in the course of switching to digital cable television since it was first introduced in the late 1990s. Most cable companies require a set-top box ( cable converter box ) or a slot on one's TV set for conditional access module cards to view their cable channels, even on newer televisions with digital cable QAM tuners, because most digital cable channels are now encrypted, or scrambled , to reduce cable service theft . A cable from
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3780-735: The audio frequencies encountered in telephony . Also at microwave frequencies, particularly the higher bands, waveguide designs can be used. Many of these waveguide couplers correspond to one of the conducting transmission line designs, but there are also types that are unique to waveguide. Directional couplers and power dividers have many applications. These include providing a signal sample for measurement or monitoring, feedback, combining feeds to and from antennas, antenna beam forming, providing taps for cable distributed systems such as cable TV, and separating transmitted and received signals on telephone lines. The symbols most often used for directional couplers are shown in figure 1. The symbol may have
3870-404: The basic selection. By subscribing to additional tiers, customers could get specialty channels, movie channels, and foreign channels. Large cable companies used addressable descramblers to limit access to premium channels for customers not subscribing to higher tiers, however the above magazines often published workarounds for that technology as well. During the 1990s, the pressure to accommodate
3960-670: The best isolation. Directivity is directly related to isolation. It is defined as: Directivity: D 3 , 4 = − 10 log ( P 4 P 3 ) = − 10 log ( P 4 P 1 ) + 10 log ( P 3 P 1 ) d B {\displaystyle D_{3,4}=-10\log {\left({\frac {P_{4}}{P_{3}}}\right)}=-10\log {\left({\frac {P_{4}}{P_{1}}}\right)}+10\log {\left({\frac {P_{3}}{P_{1}}}\right)}\quad {\rm {dB}}} where: P 3
4050-481: The branch lines. High impedance lines have narrow tracks and this usually limits the design to three sections in planar formats due to manufacturing limitations. A similar limitation applies for coupling factors looser than 10 dB ; low coupling also requires narrow tracks. Coupled lines are a better choice when loose coupling is required, but branch-line couplers are good for tight coupling and can be used for 3 dB hybrids. Branch-line couplers usually do not have such
4140-563: The cable box itself, these midband channels were used for early incarnations of pay TV , e.g. The Z Channel (Los Angeles) and HBO but transmitted in the clear i.e. not scrambled as standard TV sets of the period could not pick up the signal nor could the average consumer de-tune the normal stations to be able to receive it. Once tuners that could receive select mid-band and super-band channels began to be incorporated into standard television sets, broadcasters were forced to either install scrambling circuitry or move these signals further out of
4230-429: The cable company's local distribution facility, called the headend . Many channels can be transmitted through one coaxial cable by a technique called frequency division multiplexing . At the headend, each television channel is translated to a different frequency . By giving each channel a different frequency slot on the cable, the separate television signals do not interfere with each other. At an outdoor cable box on
4320-515: The cable to send data from the customer box to the cable headend, for advanced features such as requesting pay-per-view shows or movies, cable internet access , and cable telephone service . The downstream channels occupy a band of frequencies from approximately 50 MHz to 1 GHz, while the upstream channels occupy frequencies of 5 to 42 MHz. Subscribers pay with a monthly fee. Subscribers can choose from several levels of service, with premium packages including more channels but costing
4410-675: The case of no local CBS or ABC station being available – rebroadcast the programming from a nearby affiliate but fill in with its own news and other community programming to suit its own locale. Many live local programs with local interests were subsequently created all over the United States in most major television markets in the early 1980s. This evolved into today's many cable-only broadcasts of diverse programming, including cable-only produced television movies and miniseries . Cable specialty channels , starting with channels oriented to show movies and large sporting or performance events, diversified further, and narrowcasting became common. By
4500-508: The chosen channel into the TV set on Channel 2, 3 or 4. Initially, UHF broadcast stations were at a disadvantage because the standard TV sets in use at the time were unable to receive their channels. With the passage of the All-Channel Receiver Act in 1964, all new television sets were required to include a UHF tuner, nonetheless, it would still take a few years for UHF stations to become competitive. Before being added to
4590-1084: The closest competitor of Sky Cable the Philippines' largest cable TV company in Metro Manila. Both have their own associates all over the country and both offer high-speed cable Internet service to its respective subscribers. On November 11, 2012, Sky Cable Corporation eventually acquired the assets of Global Destiny Cable through its parent, Destiny Cable, Inc. at the cost of P3.5 billion in order to improve services to customers of Destiny Cable, UniCable, and MyDestiny broadband Internet. Global Destiny Cable has been reverted to Destiny Cable after separation from Global Cable. On November 12, 2012, Destiny Cable headquarters moved from Solid House Building in Makati to Sky Cable's headquarters in Quezon City . The NTC consummated Sky's acquisition on December 18, 2012. On November 25, 2018, Destiny Cable announced that it would discontinue its cable TV operations effective January 1, 2019. The final broadcast and sign-off of Destiny Cable
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#17327796332334680-414: The coupled line a higher impedance than the main line such as shown in figure 6. This design is advantageous where the coupler is being fed to a detector for power monitoring. The higher impedance line results in a higher RF voltage for a given main line power making the work of the detector diode easier. The frequency range specified by manufacturers is that of the coupled line. The main line response
4770-434: The coupled line a signal of the same polarity is induced on the coupled line similar to the response of an RC-high-pass. This leads to two non-inverted pulses on the coupled line that travel in opposite direction to each other. When the pulse on the main line leaves the coupled line an inverted signal is induced on the coupled line, triggering two inverted impulses that travel in opposite direction to each other. Both impulses on
4860-417: The coupled line that go in the same direction as the pulse on the main line are of opposite polarity. They cancel each other so there is no response on the exit of the coupled line in forward direction. This is the decoupled port. The pulses on the coupled line that travel in the opposite direction to the pulse on the main line are also of opposite polarity to each other but the second impulse is delayed by twice
4950-427: The coupler are treated as being sections of a filter, and by adjusting the coupling factor of each section the coupled port can be made to have any of the classic filter responses such as maximally flat ( Butterworth filter ), equal-ripple ( Cauer filter ), or a specified-ripple ( Chebychev filter ) response. Ripple is the maximum variation in output of the coupled port in its passband , usually quoted as plus or minus
5040-423: The coupling loss. In a real directional coupler, however, the insertion loss consists of a combination of coupling loss, dielectric loss, conductor loss, and VSWR loss. Depending on the frequency range, coupling loss becomes less significant above 15 dB coupling where the other losses constitute the majority of the total loss. The theoretical insertion loss (dB) vs coupling (dB) for a dissipationless coupler
5130-445: The coupling. It is used for strong couplings in the range 3 dB to 6 dB . The earliest transmission line power dividers were simple T-junctions. These suffer from very poor isolation between the output ports – a large part of the power reflected back from port 2 finds its way into port 3. It can be shown that it is not theoretically possible to simultaneously match all three ports of a passive, lossless three-port and poor isolation
5220-447: The delay of the parallel line. For a λ/4 coupled-line the total delay length is λ/2 so the second signal is inverted and this gives a maximum response on the coupled port. A single λ/4 coupled section is good for bandwidths of less than an octave. To achieve greater bandwidths multiple λ/4 coupling sections are used. The design of such couplers proceeds in much the same way as the design of distributed-element filters . The sections of
5310-451: The dielectric rather than side by side. The coupling of the two lines across their width is much greater than the coupling when they are edge-on to each other. The λ/4 coupled-line design is good for coaxial and stripline implementations but does not work so well in the now popular microstrip format, although designs do exist. The reason for this is that microstrip is not a homogeneous medium – there are two different mediums above and below
5400-415: The fact that the descrambling circuitry was for a time present in these tuners, depriving the cable operator of much of their revenue, such cable-ready tuners are rarely used now – requiring a return to the set-top boxes used from the 1970s onward. The digital television transition in the United States has put all signals, broadcast and cable, into digital form, rendering analog cable television service
5490-445: The field of radio technology. They couple a defined amount of the electromagnetic power in a transmission line to a port enabling the signal to be used in another circuit. An essential feature of directional couplers is that they only couple power flowing in one direction. Power entering the output port is coupled to the isolated port but not to the coupled port. A directional coupler designed to split power equally between two ports
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#17327796332335580-428: The form; in this article have the meaning "parameter P at port a due to an input at port b ". A symbol for power dividers is shown in figure 2. Power dividers and directional couplers are in all essentials the same class of device. Directional coupler tends to be used for 4-port devices that are only loosely coupled – that is, only a small fraction of the input power appears at the coupled port. Power divider
5670-457: The growing array of offerings resulted in digital transmission that made more efficient use of the VHF signal capacity; fibre optics was common to carry signals into areas near the home, where coax could carry higher frequencies over the short remaining distance. Although for a time in the 1980s and 1990s, television receivers and VCRs were equipped to receive the mid-band and super-band channels. Due to
5760-450: The headend, the electrical signal is translated into an optical signal and sent through the fiber. The fiber trunkline goes to several distribution hubs , from which multiple fibers fan out to carry the signal to boxes called optical nodes in local communities. At the optical node, the optical signal is translated back into an electrical signal and carried by coaxial cable distribution lines on utility poles, from which cables branch out to
5850-511: The input and the isolated ports may be different from the isolation between the two output ports. For example, the isolation between ports 1 and 4 can be 30 dB while the isolation between ports 2 and 3 can be a different value such as 25 dB . Isolation can be estimated from the coupling plus return loss . The isolation should be as high as possible. In actual couplers the isolated port is never completely isolated. Some RF power will always be present. Waveguide directional couplers will have
5940-446: The isolated port. A portion of the power applied to port 2 will be coupled to port 4. However, the device is not normally used in this mode and port 4 is usually terminated with a matched load (typically 50 ohms). This termination can be internal to the device and port 4 is not accessible to the user. Effectively, this results in a 3-port device, hence the utility of the second symbol for directional couplers in figure 1. Symbols of
6030-460: The jack in the wall is attached to the input of the box, and an output cable from the box is attached to the television, usually the RF-IN or composite input on older TVs. Since the set-top box only decodes the single channel that is being watched, each television in the house requires a separate box. Some unencrypted channels, usually traditional over-the-air broadcast networks, can be displayed without
6120-490: The late 1980s, cable-only signals outnumbered broadcast signals on cable systems, some of which by this time had expanded beyond 35 channels. By the mid-1980s in Canada, cable operators were allowed by the regulators to enter into distribution contracts with cable networks on their own. By the 1990s, tiers became common, with customers able to subscribe to different tiers to obtain different selections of additional channels above
6210-497: The lines can be run side-by-side relying on the coax outer conductors for screening. The Wilkinson power divider solves the matching problem of the simple T-junction: it has low VSWR at all ports and high isolation between output ports. The input and output impedances at each port are designed to be equal to the characteristic impedance of the microwave system. This is achieved by making the line impedance 2 {\displaystyle \scriptstyle {\sqrt {2}}} of
6300-426: The matrix main diagonal are a consequence of perfect matching – power input to any port is not reflected back to that same port. The zeroes on the matrix antidiagonal are a consequence of perfect isolation between the input and isolated port. For a passive lossless directional coupler, we must in addition have, since the power entering the input port must all leave by one of the other two ports. Insertion loss
6390-423: The maximum number of channels that could be broadcast in one city was 7: channels 2, 4, either 5 or 6, 7, 9, 11 and 13, as receivers at the time were unable to receive strong (local) signals on adjacent channels without distortion. (There were frequency gaps between 4 and 5, and between 6 and 7, which allowed both to be used in the same city). As equipment improved, all twelve channels could be utilized, except where
6480-422: The minimum track width that can be produced and also puts a limit on how close the lines can be placed to each other. This becomes a problem when very tight coupling is required and 3 dB couplers often use a different design. However, tightly coupled lines can be produced in air stripline which also permits manufacture by printed planar technology. In this design the two lines are printed on opposite sides of
6570-451: The nearest network newscast. Such stations may use similar on-air branding as that used by the nearby broadcast network affiliate, but the fact that these stations do not broadcast over the air and are not regulated by the FCC, their call signs are meaningless. These stations evolved partially into today's over-the-air digital subchannels, where a main broadcast TV station e.g. NBC 37* would – in
6660-408: The old analog cable without a set-top box. To receive digital cable channels on an analog television set, even unencrypted ones, requires a different type of box, a digital television adapter supplied by the cable company or purchased by the subscriber. Another new distribution method that takes advantage of the low cost high quality DVB distribution to residential areas, uses TV gateways to convert
6750-476: The output port. Some applications make use of this phase difference. Letting κ = i κ I {\displaystyle \kappa =i\kappa _{\mathrm {I} }\ } , the ideal case of lossless operation simplifies to, The branch-line coupler consists of two parallel transmission lines physically coupled together with two or more branch lines between them. The branch lines are spaced λ/4 apart and represent sections of
6840-451: The primary property of a directional coupler. Coupling factor is a negative quantity, it cannot exceed 0 dB for a passive device, and in practice does not exceed −3 dB since more than this would result in more power output from the coupled port than power from the transmitted port – in effect their roles would be reversed. Although a negative quantity, the minus sign is frequently dropped (but still implied) in running text and diagrams and
6930-504: The programming at the headend (the individual channels, which are distributed nationally, also have their own nationally oriented commercials). Modern cable systems are large, with a single network and headend often serving an entire metropolitan area . Most systems use hybrid fiber-coaxial (HFC) distribution; this means the trunklines that carry the signal from the headend to local neighborhoods are optical fiber to provide greater bandwidth and also extra capacity for future expansion. At
7020-454: The programming without cost. Later, the cable operators began to carry FM radio stations, and encouraged subscribers to connect their FM stereo sets to cable. Before stereo and bilingual TV sound became common, Pay-TV channel sound was added to the FM stereo cable line-ups. About this time, operators expanded beyond the 12-channel dial to use the midband and superband VHF channels adjacent to
7110-476: The range of reception for early cable-ready TVs and VCRs. However, once consumer sets had the ability to receive all 181 FCC allocated channels, premium broadcasters were left with no choice but to scramble. The descrambling circuitry was often published in electronics hobby magazines such as Popular Science and Popular Electronics allowing anybody with anything more than a rudimentary knowledge of broadcast electronics to be able to build their own and receive
7200-418: The signals are typically encrypted on modern digital cable systems, and the set-top box must be activated by an activation code sent by the cable company before it will function, which is only sent after the subscriber signs up. If the subscriber fails to pay their bill, the cable company can send a signal to deactivate the subscriber's box, preventing reception. There are also usually upstream channels on
7290-403: The subscriber's residence, the company's service drop cable is connected to cables distributing the signal to different rooms in the building. At each television, the subscriber's television or a set-top box provided by the cable company translates the desired channel back to its original frequency ( baseband ), and it is displayed onscreen. Due to widespread cable theft in earlier analog systems,
7380-404: The television operations of the two companies, of which operates the cable providers; Global Cable and Destiny Cable. In November 2000 Destiny Cable formed a partnership with Global Cable to further strengthen and systematize its cable television ventures. However, it was only on November 2, 2003, that the corporate name was changed to Global Destiny Cable. Global Destiny Cable is perceived to be
7470-451: The transmission strip. This leads to transmission modes other than the usual TEM mode found in conductive circuits. The propagation velocities of even and odd modes are different leading to signal dispersion. A better solution for microstrip is a coupled line much shorter than λ/4, shown in figure 5, but this has the disadvantage of a coupling factor which rises noticeably with frequency. A variation of this design sometimes encountered has
7560-506: The two output ports. In this case, one of the output ports is used as the input; the other is considered the output port while the other two ports (input and isolated) are terminated by matched loads. Consequently: I 3 , 2 = − 10 log ( P 3 P 2 ) d B {\displaystyle I_{3,2}=-10\log {\left({\frac {P_{3}}{P_{2}}}\right)}\quad {\rm {dB}}} The isolation between
7650-414: The two outputs are each half the input power. This synonymously meant a quadrature 3 dB coupler with outputs 90° out of phase. Now any matched 4-port with isolated arms and equal power division is called a hybrid or hybrid coupler. Other types can have different phase relationships. If 90°, it is a 90° hybrid, if 180°, a 180° hybrid and so on. In this article hybrid coupler without qualification means
7740-459: The two paths through it. The design is a 3-branch coupler equivalent to two 3 dB 90° hybrid couplers connected in cascade . The result is effectively a 0 dB coupler. It will cross over the inputs to the diagonally opposite outputs with a phase delay of 90° in both lines. The construction of the Lange coupler is similar to the interdigital filter with paralleled lines interleaved to achieve
7830-532: The upstream speed to 31.2 Kbp/s and prevented the always-on convenience broadband internet typically provides. Many large cable systems have upgraded or are upgrading their equipment to allow for bi-directional signals, thus allowing for greater upload speed and always-on convenience, though these upgrades are expensive. In North America , Australia and Europe , many cable operators have already introduced cable telephone service, which operates just like existing fixed line operators. This service involves installing
7920-427: Was limited, meaning frequencies over 250 MHz were difficult to transmit to distant portions of the coaxial network, and UHF channels could not be used at all. To expand beyond 12 channels, non-standard midband channels had to be used, located between the FM band and Channel 7, or superband beyond Channel 13 up to about 300 MHz; these channels initially were only accessible using separate tuner boxes that sent
8010-559: Was mainly used to relay terrestrial channels in geographical areas poorly served by terrestrial television signals. Cable television began in the United States as a commercial business in 1950s. The early systems simply received weak ( broadcast ) channels, amplified them, and sent them over unshielded wires to the subscribers, limited to a community or to adjacent communities. The receiving antenna would be taller than any individual subscriber could afford, thus bringing in stronger signals; in hilly or mountainous terrain it would be placed at
8100-415: Was scheduled for December 31, 2018, at 11:59 p.m. Cable television A cable channel (sometimes known as a cable network ) is a television network available via cable television. Many of the same channels are distributed through satellite television . Alternative terms include non-broadcast channel or programming service , the latter being mainly used in legal contexts. The abbreviation CATV
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