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95-456: The AC Locomotive Group is a dedicated AC electric locomotive preservation society in England. It has five locomotives in its care: 81002 , 82008 , 83012 , 85101 and 89001 . In 1996, Pete Waterman , who had purchased the sole surviving examples of AC electric classes 81 , 82 , 83 and 85 , put his entire fleet of locomotives for sale. The AC Locomotive Group (ACLG) was formed with

190-403: A balanced signaling system, so that the two wires carry equal but opposite currents. Each wire in a twisted pair radiates a signal, but it is effectively cancelled by radiation from the other wire, resulting in almost no radiation loss. Coaxial cables are commonly used at audio frequencies and above for convenience. A coaxial cable has a conductive wire inside a conductive tube, separated by

285-441: A constellation diagram , showing the amplitude of the I signal at the x-axis, and the amplitude of the Q signal at the y-axis, for each symbol. PSK and ASK, and sometimes also FSK, are often generated and detected using the principle of QAM. The I and Q signals can be combined into a complex-valued signal I + jQ (where j is the imaginary unit ). The resulting so called equivalent lowpass signal or equivalent baseband signal

380-448: A dielectric layer. The current flowing on the surface of the inner conductor is equal and opposite to the current flowing on the inner surface of the outer tube. The electromagnetic field is thus completely contained within the tube, and (ideally) no energy is lost to radiation or coupling outside the tube. Coaxial cables have acceptably small losses for frequencies up to about 5 GHz. For microwave frequencies greater than 5 GHz,

475-477: A power plant , energy is generated at a convenient voltage for the design of a generator , and then stepped up to a high voltage for transmission. Near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer voltages vary somewhat depending on the country and size of load, but generally motors and lighting are built to use up to a few hundred volts between phases. The voltage delivered to equipment such as lighting and motor loads

570-513: A challenging topic in telecommunication systems and computer engineering. Such systems have many civil and military applications. Moreover, blind recognition of modulation type is an important problem in commercial systems, especially in software-defined radio . Usually in such systems, there are some extra information for system configuration, but considering blind approaches in intelligent receivers, we can reduce information overload and increase transmission performance. Obviously, with no knowledge of

665-440: A compromise between low frequency for traction and heavy induction motors, while still allowing incandescent lighting to operate (although with noticeable flicker). Most of the 25 Hz residential and commercial customers for Niagara Falls power were converted to 60 Hz by the late 1950s, although some 25 Hz industrial customers still existed as of the start of the 21st century. 16.7 Hz power (formerly 16 2/3 Hz)

760-439: A computer. This carrier wave usually has a much higher frequency than the message signal does. This is because it is impractical to transmit signals with low frequencies. Generally, to receive a radio wave one needs a radio antenna with length that is one-fourth of wavelength. For low frequency radio waves, wavelength is on the scale of kilometers and building such a large antenna is not practical. In radio communication ,

855-534: A cosine waveform) and a quadrature phase signal (or Q, with an example being a sine wave) are amplitude modulated with a finite number of amplitudes and then summed. It can be seen as a two-channel system, each channel using ASK. The resulting signal is equivalent to a combination of PSK and ASK. In all of the above methods, each of these phases, frequencies or amplitudes are assigned a unique pattern of binary bits . Usually, each phase, frequency or amplitude encodes an equal number of bits. This number of bits comprises

950-490: A direct current does not create electromagnetic waves. At very high frequencies, the current no longer flows in the wire, but effectively flows on the surface of the wire, within a thickness of a few skin depths . The skin depth is the thickness at which the current density is reduced by 63%. Even at relatively low frequencies used for power transmission (50 Hz – 60 Hz), non-uniform distribution of current still occurs in sufficiently thick conductors . For example,

1045-516: A discrete alphabet to be transmitted. This alphabet can consist of a set of real or complex numbers , or sequences, like oscillations of different frequencies, so-called frequency-shift keying (FSK) modulation. A more complicated digital modulation method that employs multiple carriers, orthogonal frequency-division multiplexing (OFDM), is used in WiFi networks, digital radio stations and digital cable television transmission. In analog modulation,

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1140-412: A finite number of M alternative symbols (the modulation alphabet ). A simple example: A telephone line is designed for transferring audible sounds, for example, tones, and not digital bits (zeros and ones). Computers may, however, communicate over a telephone line by means of modems, which are representing the digital bits by tones, called symbols. If there are four alternative symbols (corresponding to

1235-437: A form of dielectric waveguides, can be used. For such frequencies, the concepts of voltages and currents are no longer used. Alternating currents are accompanied (or caused) by alternating voltages. An AC voltage v can be described mathematically as a function of time by the following equation: where The peak-to-peak value of an AC voltage is defined as the difference between its positive peak and its negative peak. Since

1330-459: A higher voltage requires less loss-producing current than for the same power at a lower voltage. Power is often transmitted at hundreds of kilovolts on pylons , and transformed down to tens of kilovolts to be transmitted on lower level lines, and finally transformed down to 100 V – 240 V for domestic use. High voltages have disadvantages, such as the increased insulation required, and generally increased difficulty in their safe handling. In

1425-957: A lighting system where sets of induction coils were installed along a high voltage AC line. Instead of changing voltage, the primary windings transferred power to the secondary windings which were connected to one or several 'electric candles' (arc lamps) of his own design, used to keep the failure of one lamp from disabling the entire circuit. In 1878, the Ganz factory , Budapest, Hungary, began manufacturing equipment for electric lighting and, by 1883, had installed over fifty systems in Austria-Hungary . Their AC systems used arc and incandescent lamps, generators, and other equipment. Alternating current systems can use transformers to change voltage from low to high level and back, allowing generation and consumption at low voltages but transmission, possibly over great distances, at high voltage, with savings in

1520-412: A musical instrument that can generate four different tones, one at a time), the first symbol may represent the bit sequence 00, the second 01, the third 10 and the fourth 11. If the modem plays a melody consisting of 1000 tones per second, the symbol rate is 1000 symbols/second, or 1000 baud . Since each tone (i.e., symbol) represents a message consisting of two digital bits in this example, the bit rate

1615-429: A narrowband analog signal over an analog baseband channel as a two-level signal by modulating a pulse wave . Some pulse modulation schemes also allow the narrowband analog signal to be transferred as a digital signal (i.e., as a quantized discrete-time signal ) with a fixed bit rate, which can be transferred over an underlying digital transmission system, for example, some line code . These are not modulation schemes in

1710-417: A periodic waveform , called the carrier signal , with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone , a video signal representing moving images from a video camera , or a digital signal representing a sequence of binary digits, a bitstream from

1805-597: A proper class. Another recent approach is based on feature extraction. Digital baseband modulation changes the characteristics of a baseband signal, i.e., one without a carrier at a higher frequency. This can be used as equivalent signal to be later frequency-converted to a carrier frequency, or for direct communication in baseband. The latter methods both involve relatively simple line codes , as often used in local buses, and complicated baseband signalling schemes such as used in DSL . Pulse modulation schemes aim at transferring

1900-565: A single cable to customers. Since each carrier occupies a different frequency, the channels do not interfere with each other. At the destination end, the carrier signal is demodulated to extract the information bearing modulation signal. A modulator is a device or circuit that performs modulation. A demodulator (sometimes detector ) is a circuit that performs demodulation , the inverse of modulation. A modem (from mod ulator– dem odulator), used in bidirectional communication, can perform both operations. The lower frequency band occupied by

1995-522: A single center-tapped transformer giving two live conductors, is a common distribution scheme for residential and small commercial buildings in North America. This arrangement is sometimes incorrectly referred to as "two phase". A similar method is used for a different reason on construction sites in the UK. Small power tools and lighting are supposed to be supplied by a local center-tapped transformer with

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2090-555: A voltage of 55 V between each power conductor and earth. This significantly reduces the risk of electric shock in the event that one of the live conductors becomes exposed through an equipment fault whilst still allowing a reasonable voltage of 110 V between the two conductors for running the tools. A third wire , called the bond (or earth) wire, is often connected between non-current-carrying metal enclosures and earth ground. This conductor provides protection from electric shock due to accidental contact of circuit conductors with

2185-403: A wire that is made of a non-perfect conductor (a conductor with finite, rather than infinite, electrical conductivity) pushes the alternating current, along with their associated electromagnetic fields, away from the wire's center. The phenomenon of alternating current being pushed away from the center of the conductor is called skin effect , and a direct current does not exhibit this effect, since

2280-470: Is 230 × R × W × 2 {\displaystyle 230\times R\times W\times 2} , that is 460 RW. During the course of one cycle (two cycle as the power) the voltage rises from zero to 325 V, the power from zero to 460 RW, and both falls through zero. Next, the voltage descends to reverse direction, -325 V, but the power ascends again to 460 RW, and both returns to zero. Alternating current

2375-425: Is synchronous modulation . The most common digital modulation techniques are: MSK and GMSK are particular cases of continuous phase modulation. Indeed, MSK is a particular case of the sub-family of CPM known as continuous-phase frequency-shift keying (CPFSK) which is defined by a rectangular frequency pulse (i.e. a linearly increasing phase pulse) of one-symbol-time duration (total response signaling). OFDM

2470-444: Is a complex-valued representation of the real-valued modulated physical signal (the so-called passband signal or RF signal ). These are the general steps used by the modulator to transmit data: At the receiver side, the demodulator typically performs: As is common to all digital communication systems, the design of both the modulator and demodulator must be done simultaneously. Digital modulation schemes are possible because

2565-425: Is based on the idea of frequency-division multiplexing (FDM), but the multiplexed streams are all parts of a single original stream. The bit stream is split into several parallel data streams, each transferred over its own sub-carrier using some conventional digital modulation scheme. The modulated sub-carriers are summed to form an OFDM signal. This dividing and recombining help with handling channel impairments. OFDM

2660-530: Is called Litz wire . This measure helps to partially mitigate skin effect by forcing more equal current throughout the total cross section of the stranded conductors. Litz wire is used for making high-Q inductors , reducing losses in flexible conductors carrying very high currents at lower frequencies, and in the windings of devices carrying higher radio frequency current (up to hundreds of kilohertz), such as switch-mode power supplies and radio frequency transformers . As written above, an alternating current

2755-407: Is considered as a modulation technique rather than a multiplex technique since it transfers one bit stream over one communication channel using one sequence of so-called OFDM symbols. OFDM can be extended to multi-user channel access method in the orthogonal frequency-division multiple access (OFDMA) and multi-carrier code-division multiple access (MC-CDMA) schemes, allowing several users to share

2850-505: Is distributed as alternating current because AC voltage may be increased or decreased with a transformer . This allows the power to be transmitted through power lines efficiently at high voltage , which reduces the energy lost as heat due to resistance of the wire, and transformed to a lower, safer voltage for use. Use of a higher voltage leads to significantly more efficient transmission of power. The power losses ( P w {\displaystyle P_{\rm {w}}} ) in

2945-439: Is double of the one of the voltage's. To illustrate these concepts, consider a 230 V AC mains supply used in many countries around the world. It is so called because its root mean square value is 230 V. This means that the time-averaged power delivered P average {\displaystyle P_{\text{average}}} is equivalent to the power delivered by a DC voltage of 230 V. To determine

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3040-828: Is in the final stages of an overhaul to return it to main line operation. Alternating current The usual waveform of alternating current in most electric power circuits is a sine wave , whose positive half-period corresponds with positive direction of the current and vice versa (the full period is called a cycle ). In certain applications, like guitar amplifiers , different waveforms are used, such as triangular waves or square waves . Audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information such as sound (audio) or images (video) sometimes carried by modulation of an AC carrier signal. These currents typically alternate at higher frequencies than those used in power transmission. Electrical energy

3135-469: Is made of electric charge under periodic acceleration , which causes radiation of electromagnetic waves . Energy that is radiated is lost. Depending on the frequency, different techniques are used to minimize the loss due to radiation. At frequencies up to about 1 GHz, pairs of wires are twisted together in a cable, forming a twisted pair . This reduces losses from electromagnetic radiation and inductive coupling . A twisted pair must be used with

3230-521: Is probably by Guillaume Duchenne , inventor and developer of electrotherapy . In 1855, he announced that AC was superior to direct current for electrotherapeutic triggering of muscle contractions. Alternating current technology was developed further by the Hungarian Ganz Works company (1870s), and in the 1880s: Sebastian Ziani de Ferranti , Lucien Gaulard , and Galileo Ferraris . In 1876, Russian engineer Pavel Yablochkov invented

3325-446: Is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world. High-voltage direct-current (HVDC) electric power transmission systems have become more viable as technology has provided efficient means of changing the voltage of DC power. Transmission with high voltage direct current

3420-568: Is still used in some European rail systems, such as in Austria , Germany , Norway , Sweden and Switzerland . Off-shore, military, textile industry, marine, aircraft, and spacecraft applications sometimes use 400 Hz, for benefits of reduced weight of apparatus or higher motor speeds. Computer mainframe systems were often powered by 400 Hz or 415 Hz for benefits of ripple reduction while using smaller internal AC to DC conversion units. A direct current flows uniformly throughout

3515-422: Is therefore V peak − ( − V peak ) = 2 V peak {\displaystyle V_{\text{peak}}-(-V_{\text{peak}})=2V_{\text{peak}}} . Below an AC waveform (with no DC component ) is assumed. The RMS voltage is the square root of the mean over one cycle of the square of the instantaneous voltage. The relationship between voltage and

3610-554: Is twice the symbol rate, i.e. 2000 bits per second. According to one definition of digital signal , the modulated signal is a digital signal. According to another definition, the modulation is a form of digital-to-analog conversion . Most textbooks would consider digital modulation schemes as a form of digital transmission , synonymous to data transmission; very few would consider it as analog transmission . The most fundamental digital modulation techniques are based on keying : In QAM, an in-phase signal (or I, with one example being

3705-425: Is used to transmit information , as in the cases of telephone and cable television . Information signals are carried over a wide range of AC frequencies. POTS telephone signals have a frequency of about 3 kHz, close to the baseband audio frequency. Cable television and other cable-transmitted information currents may alternate at frequencies of tens to thousands of megahertz. These frequencies are similar to

3800-849: The Westinghouse Electric in Pittsburgh, Pennsylvania, on January 8, 1886. The new firm became active in developing alternating current (AC) electric infrastructure throughout the United States. The Edison Electric Light Company held an option on the US rights for the Ganz ZBD transformers, requiring Westinghouse to pursue alternative designs on the same principles. George Westinghouse had bought Gaulard and Gibbs' patents for $ 50,000 in February 1886. He assigned to William Stanley

3895-468: The frequency of the carrier wave is varied by the modulation signal. These were the earliest types of modulation , and are used to transmit an audio signal representing sound in AM and FM radio broadcasting . More recent systems use digital modulation , which impresses a digital signal consisting of a sequence of binary digits (bits), a bitstream , on the carrier, by means of mapping bits to elements from

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3990-411: The symbol that is represented by the particular phase, frequency or amplitude. If the alphabet consists of M = 2 N {\displaystyle M=2^{N}} alternative symbols, each symbol represents a message consisting of N bits. If the symbol rate (also known as the baud rate ) is f S {\displaystyle f_{S}} symbols/second (or baud ),

4085-752: The AC system at the Grosvenor Gallery power station in 1886 for the London Electric Supply Corporation (LESCo) including alternators of his own design and open core transformer designs with serial connections for utilization loads - similar to Gaulard and Gibbs. In 1890, he designed their power station at Deptford and converted the Grosvenor Gallery station across the Thames into an electrical substation , showing

4180-520: The QAM modulation principle are used to drive switching amplifiers with these FM and other waveforms, and sometimes QAM demodulators are used to receive the signals put out by these switching amplifiers. Automatic digital modulation recognition in intelligent communication systems is one of the most important issues in software-defined radio and cognitive radio . According to incremental expanse of intelligent receivers, automatic modulation recognition becomes

4275-413: The biggest difference being that waveguides have no inner conductor. Waveguides can have any arbitrary cross section, but rectangular cross sections are the most common. Because waveguides do not have an inner conductor to carry a return current, waveguides cannot deliver energy by means of an electric current , but rather by means of a guided electromagnetic field . Although surface currents do flow on

4370-547: The city of Pomona, California , which was 14 miles away. Meanwhile, the possibility of transferring electrical power from a waterfall at a distance was explored at the Grängesberg mine in Sweden. A 45  m fall at Hällsjön, Smedjebackens kommun, where a small iron work had been located, was selected. In 1893, a three-phase 9.5  kv system was used to transfer 400 horsepower a distance of 15  km , becoming

4465-507: The cost of conductors and energy losses. A bipolar open-core power transformer developed by Lucien Gaulard and John Dixon Gibbs was demonstrated in London in 1881, and attracted the interest of Westinghouse . They also exhibited the invention in Turin in 1884. However, these early induction coils with open magnetic circuits are inefficient at transferring power to loads . Until about 1880,

4560-514: The cross-section of a homogeneous electrically conducting wire. An alternating current of any frequency is forced away from the wire's center, toward its outer surface. This is because an alternating current (which is the result of the acceleration of electric charge ) creates electromagnetic waves (a phenomenon known as electromagnetic radiation ). Electric conductors are not conducive to electromagnetic waves (a perfect electric conductor prohibits all electromagnetic waves within its boundary), so

4655-411: The cross-sectional area. A conductor's AC resistance is higher than its DC resistance, causing a higher energy loss due to ohmic heating (also called I R loss). For low to medium frequencies, conductors can be divided into stranded wires, each insulated from the others, with the relative positions of individual strands specially arranged within the conductor bundle. Wire constructed using this technique

4750-407: The data rate is N f S {\displaystyle Nf_{S}} bit/second. For example, with an alphabet consisting of 16 alternative symbols, each symbol represents 4 bits. Thus, the data rate is four times the baud rate. In the case of PSK, ASK or QAM, where the carrier frequency of the modulated signal is constant, the modulation alphabet is often conveniently represented on

4845-476: The design of electric motors, particularly for hoisting, crushing and rolling applications, and commutator-type traction motors for applications such as railways . However, low frequency also causes noticeable flicker in arc lamps and incandescent light bulbs . The use of lower frequencies also provided the advantage of lower transmission losses, which are proportional to frequency. The original Niagara Falls generators were built to produce 25 Hz power, as

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4940-508: The electrical system to a safe state. All bond wires are bonded to ground at the main service panel, as is the neutral/identified conductor if present. The frequency of the electrical system varies by country and sometimes within a country; most electric power is generated at either 50 or 60  Hertz . Some countries have a mixture of 50 Hz and 60 Hz supplies, notably electricity power transmission in Japan . A low frequency eases

5035-522: The electromagnetic wave frequencies often used to transmit the same types of information over the air . The first alternator to produce alternating current was an electric generator based on Michael Faraday 's principles constructed by the French instrument maker Hippolyte Pixii in 1832. Pixii later added a commutator to his device to produce the (then) more commonly used direct current. The earliest recorded practical application of alternating current

5130-414: The experiments; In their joint 1885 patent applications for novel transformers (later called ZBD transformers), they described two designs with closed magnetic circuits where copper windings were either wound around a ring core of iron wires or else surrounded by a core of iron wires. In both designs, the magnetic flux linking the primary and secondary windings traveled almost entirely within the confines of

5225-479: The first commercial application. In 1893, Westinghouse built an alternating current system for the Chicago World Exposition . In 1893, Decker designed the first American commercial three-phase power plant using alternating current—the hydroelectric Mill Creek No. 1 Hydroelectric Plant near Redlands, California . Decker's design incorporated 10 kV three-phase transmission and established

5320-512: The group purchased 86101 and 86213. At the end of 2006 GNER put 89001 up for sale, and following a high-profile appeal, the ACLG successfully purchased the loco for preservation. In 2008, the group was able to acquire the loco that carried its name, 87002, for preservation. For four months in early 2008, 86101 operated services from London King's Cross to Doncaster hauling Cargo-D Mark 3s under hire to First Hull Trains . In February 2016, 86213

5415-443: The group while in 2004, 86401 was purchased. The same year, GNER placed 89001 into the group's care following closure of part of Doncaster Works where it had been stored out of use. In 2005 the ACLG was honoured by the naming of 87002 as The AC Locomotive Group . This was owned by Porterbrook and painted in its purple colour scheme, and later became the last Class 87 to haul a passenger train in regular service. Also in 2005,

5510-564: The inner walls of the waveguides, those surface currents do not carry power. Power is carried by the guided electromagnetic fields. The surface currents are set up by the guided electromagnetic fields and have the effect of keeping the fields inside the waveguide and preventing leakage of the fields to the space outside the waveguide. Waveguides have dimensions comparable to the wavelength of the alternating current to be transmitted, so they are feasible only at microwave frequencies. In addition to this mechanical feasibility, electrical resistance of

5605-651: The intention of purchasing all four machines. This was accomplished in June 1997, and three of the four locomotives were moved to Barrow Hill Engine Shed in December 1998, with the fourth joining them in early 2000. Also between 2000 and 2008, the group had 84001 on loan from the National Railway Museum , and this was given a major cosmetic overhaul following a long period stored in the open. In 2002, leasing company HSBC Rail UK placed 86213 on loan to

5700-511: The iron core, with no intentional path through air (see toroidal cores ). The new transformers were 3.4 times more efficient than the open-core bipolar devices of Gaulard and Gibbs. The Ganz factory in 1884 shipped the world's first five high-efficiency AC transformers. This first unit had been manufactured to the following specifications: 1,400 W, 40 Hz, 120:72 V, 11.6:19.4 A, ratio 1.67:1, one-phase, shell form. The ZBD patents included two other major interrelated innovations: one concerning

5795-625: The limitations of the direct current system. In 1886, the ZBD engineers designed the world's first power station that used AC generators to power a parallel-connected common electrical network, the steam-powered Rome-Cerchi power plant. The reliability of the AC technology received impetus after the Ganz Works electrified a large European metropolis: Rome in 1886. Building on the advancement of AC technology in Europe, George Westinghouse founded

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5890-429: The losses (due mainly to the dielectric separating the inner and outer tubes being a non-ideal insulator) become too large, making waveguides a more efficient medium for transmitting energy. Coaxial cables often use a perforated dielectric layer to separate the inner and outer conductors in order to minimize the power dissipated by the dielectric. Waveguides are similar to coaxial cables, as both consist of tubes, with

5985-419: The lower speed is preferable for larger machines. If the load on a three-phase system is balanced equally among the phases, no current flows through the neutral point . Even in the worst-case unbalanced (linear) load, the neutral current will not exceed the highest of the phase currents. Non-linear loads (e.g. the switch-mode power supplies widely used) may require an oversized neutral bus and neutral conductor in

6080-484: The main street of Great Barrington. The spread of Westinghouse and other AC systems triggered a push back in late 1887 by Thomas Edison (a proponent of direct current), who attempted to discredit alternating current as too dangerous in a public campaign called the " war of the currents ". In 1888, alternating current systems gained further viability with introduction of a functional AC motor , something these systems had lacked up till then. The design, an induction motor ,

6175-538: The maximum value of sin ⁡ ( x ) {\displaystyle \sin(x)} is +1 and the minimum value is −1, an AC voltage swings between + V peak {\displaystyle +V_{\text{peak}}} and − V peak {\displaystyle -V_{\text{peak}}} . The peak-to-peak voltage, usually written as V pp {\displaystyle V_{\text{pp}}} or V P-P {\displaystyle V_{\text{P-P}}} ,

6270-469: The metal chassis of portable appliances and tools. Bonding all non-current-carrying metal parts into one complete system ensures there is always a low electrical impedance path to ground sufficient to carry any fault current for as long as it takes for the system to clear the fault. This low impedance path allows the maximum amount of fault current, causing the overcurrent protection device (breakers, fuses) to trip or burn out as quickly as possible, bringing

6365-416: The modulated carrier is transmitted through space as a radio wave to a radio receiver . Another purpose of modulation is to transmit multiple channels of information through a single communication medium , using frequency-division multiplexing (FDM). For example, in cable television (which uses FDM), many carrier signals, each modulated with a different television channel , are transported through

6460-426: The modulation is applied continuously in response to the analog information signal. Common analog modulation techniques include: In digital modulation, an analog carrier signal is modulated by a discrete signal. Digital modulation methods can be considered as digital-to-analog conversion and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from

6555-405: The modulation signal is called the baseband , while the higher frequency band occupied by the modulated carrier is called the passband . In analog modulation , an analog modulation signal is "impressed" on the carrier. Examples are amplitude modulation (AM) in which the amplitude (strength) of the carrier wave is varied by the modulation signal, and frequency modulation (FM) in which

6650-425: The non-ideal metals forming the walls of the waveguide causes dissipation of power (surface currents flowing on lossy conductors dissipate power). At higher frequencies, the power lost to this dissipation becomes unacceptably large. At frequencies greater than 200 GHz, waveguide dimensions become impractically small, and the ohmic losses in the waveguide walls become large. Instead, fiber optics , which are

6745-435: The paradigm for AC power transmission from a high voltage supply to a low voltage load was a series circuit. Open-core transformers with a ratio near 1:1 were connected with their primaries in series to allow use of a high voltage for transmission while presenting a low voltage to the lamps. The inherent flaw in this method was that turning off a single lamp (or other electric device) affected the voltage supplied to all others on

6840-431: The peak voltage (amplitude), we can rearrange the above equation to: For 230 V AC, the peak voltage V peak {\displaystyle V_{\text{peak}}} is therefore 230  V × 2 {\displaystyle 230{\text{ V}}\times {\sqrt {2}}} , which is about 325 V, and the peak power P peak {\displaystyle P_{\text{peak}}}

6935-610: The power delivered is: where R {\displaystyle R} represents a load resistance. Rather than using instantaneous power, p ( t ) {\displaystyle p(t)} , it is more practical to use a time-averaged power (where the averaging is performed over any integer number of cycles). Therefore, AC voltage is often expressed as a root mean square (RMS) value, written as V rms {\displaystyle V_{\text{rms}}} , because For this reason, AC power's waveform becomes Full-wave rectified sine, and its fundamental frequency

7030-401: The restoration of auxiliary equipment (including cooling fans) in locomotives 82008 and 83012. In 2006, 81002 was completed electrically to a condition where it could be powered up from the overhead wires. Most locomotives in the collection have received full cosmetic overhauls since acquisition, with both 82008 and 85101 receiving fictitious makeovers for various periods. As at June 2020, 89001

7125-492: The same circuit. Many adjustable transformer designs were introduced to compensate for this problematic characteristic of the series circuit, including those employing methods of adjusting the core or bypassing the magnetic flux around part of a coil. The direct current systems did not have these drawbacks, giving it significant advantages over early AC systems. In the UK, Sebastian de Ferranti , who had been developing AC generators and transformers in London since 1882, redesigned

7220-414: The same phases with reverse polarity and so can be simply wired together. In practice, higher "pole orders" are commonly used. For example, a 12-pole machine would have 36 coils (10° spacing). The advantage is that lower rotational speeds can be used to generate the same frequency. For example, a 2-pole machine running at 3600 rpm and a 12-pole machine running at 600 rpm produce the same frequency;

7315-541: The same physical medium by giving different sub-carriers or spreading codes to different users. Of the two kinds of RF power amplifier , switching amplifiers ( Class D amplifiers ) cost less and use less battery power than linear amplifiers of the same output power. However, they only work with relatively constant-amplitude-modulation signals such as angle modulation (FSK or PSK) and CDMA , but not with QAM and OFDM. Nevertheless, even though switching amplifiers are completely unsuitable for normal QAM constellations, often

7410-411: The skin depth of a copper conductor is approximately 8.57 mm at 60 Hz, so high current conductors are usually hollow to reduce their mass and cost. This tendency of alternating current to flow predominantly in the periphery of conductors reduces the effective cross-section of the conductor. This increases the effective AC resistance of the conductor, since resistance is inversely proportional to

7505-585: The standards for the complete system of generation, transmission and motors used in USA today. The original Niagara Falls Adams Power Plant with three two-phase generators was put into operation in August 1895, but was connected to the remote transmission system only in 1896. The Jaruga Hydroelectric Power Plant in Croatia was set in operation two days later, on 28 August 1895. Its generator (42 Hz, 240 kW)

7600-410: The supply side. For smaller customers (just how small varies by country and age of the installation) only a single phase and neutral, or two phases and neutral, are taken to the property. For larger installations all three phases and neutral are taken to the main distribution panel. From the three-phase main panel, both single and three-phase circuits may lead off. Three-wire single-phase systems, with

7695-646: The task of redesigning the Gaulard and Gibbs transformer for commercial use in United States. On March 20, 1886, Stanley conducted a demonstrative experiment in Great Barrington : A Siemens generator's voltage of 500 volts was converted into 3000 volts, and then the voltage was stepped down to 500 volts by six Westinghouse transformers. With this setup, the Westinghouse company successfully powered thirty 100-volt incandescent bulbs in twenty shops along

7790-408: The theoretical basis of alternating current calculations include Charles Steinmetz , Oliver Heaviside , and many others. Calculations in unbalanced three-phase systems were simplified by the symmetrical components methods discussed by Charles LeGeyt Fortescue in 1918. Modulation In electronics and telecommunications , modulation is the process of varying one or more properties of

7885-496: The transmitted data and many unknown parameters at the receiver, such as the signal power, carrier frequency and phase offsets, timing information, etc., blind identification of the modulation is made fairly difficult. This becomes even more challenging in real-world scenarios with multipath fading, frequency-selective and time-varying channels. There are two main approaches to automatic modulation recognition. The first approach uses likelihood-based methods to assign an input signal to

7980-549: The transmitter-receiver pair has prior knowledge of how data is encoded and represented in the communications system. In all digital communication systems, both the modulator at the transmitter and the demodulator at the receiver are structured so that they perform inverse operations. Asynchronous methods do not require a receiver reference clock signal that is phase synchronized with the sender carrier signal . In this case, modulation symbols (rather than bits, characters, or data packets) are asynchronously transferred. The opposite

8075-403: The upstream distribution panel to handle harmonics . Harmonics can cause neutral conductor current levels to exceed that of one or all phase conductors. For three-phase at utilization voltages a four-wire system is often used. When stepping down three-phase, a transformer with a Delta (3-wire) primary and a Star (4-wire, center-earthed) secondary is often used so there is no need for a neutral on

8170-578: The use of parallel connected, instead of series connected, utilization loads, the other concerning the ability to have high turns ratio transformers such that the supply network voltage could be much higher (initially 1400 V to 2000 V) than the voltage of utilization loads (100 V initially preferred). When employed in parallel connected electric distribution systems, closed-core transformers finally made it technically and economically feasible to provide electric power for lighting in homes, businesses and public spaces. The other essential milestone

8265-519: The way to integrate older plants into a universal AC supply system. In the autumn of 1884, Károly Zipernowsky , Ottó Bláthy and Miksa Déri (ZBD), three engineers associated with the Ganz Works of Budapest, determined that open-core devices were impractical, as they were incapable of reliably regulating voltage. Bláthy had suggested the use of closed cores, Zipernowsky had suggested the use of parallel shunt connections , and Déri had performed

8360-477: The wire are a product of the square of the current ( I ) and the resistance (R) of the wire, described by the formula: This means that when transmitting a fixed power on a given wire, if the current is halved (i.e. the voltage is doubled), the power loss due to the wire's resistance will be reduced to one quarter. The power transmitted is equal to the product of the current and the voltage (assuming no phase difference); that is, Consequently, power transmitted at

8455-560: Was independently invented by Galileo Ferraris and Nikola Tesla (with Tesla's design being licensed by Westinghouse in the US). This design was independently further developed into the modern practical three-phase form by Mikhail Dolivo-Dobrovolsky and Charles Eugene Lancelot Brown in Germany on one side, and Jonas Wenström in Sweden on the other, though Brown favoured the two-phase system. A long-distance alternating current transmission

8550-547: Was installed in Telluride Colorado. The first three-phase system was established in 1891 in Frankfurt , Germany. The Tivoli – Rome transmission was completed in 1892. The San Antonio Canyon Generator was the third commercial single-phase hydroelectric AC power plant in the United States to provide long-distance electricity. It was completed on December 31, 1892, by Almarian William Decker to provide power to

8645-507: Was made and installed by the Hungarian company Ganz , while the transmission line from the power plant to the City of Šibenik was 11.5 kilometers (7.1 mi) long, and the municipal distribution grid 3000 V/110 V included six transforming stations. Alternating current circuit theory developed rapidly in the latter part of the 19th and early 20th century. Notable contributors to

8740-596: Was not feasible in the early days of electric power transmission , as there was then no economically viable way to step the voltage of DC down for end user applications such as lighting incandescent bulbs. Three-phase electrical generation is very common. The simplest way is to use three separate coils in the generator stator , physically offset by an angle of 120° (one-third of a complete 360° phase) to each other. Three current waveforms are produced that are equal in magnitude and 120° out of phase to each other. If coils are added opposite to these (60° spacing), they generate

8835-525: Was sold for export to Bulgaria. The ACLG hired 86101, 86401 and 87002 to main-line operator Electric Traction Limited for use on Caledonian Sleeper services from London Euston to Edinburgh and Glasgow between 2015 and 2019. After this work ceased in May 2019, 86101 and 87002 were sold to Locomotive Services and 86401 to West Coast Railways . The ACLG made great strides to restore electrical equipment in their early locomotives; early successes included

8930-506: Was the introduction of 'voltage source, voltage intensive' (VSVI) systems' by the invention of constant voltage generators in 1885. In early 1885, the three engineers also eliminated the problem of eddy current losses with the invention of the lamination of electromagnetic cores. Ottó Bláthy also invented the first AC electricity meter . The AC power system was developed and adopted rapidly after 1886 due to its ability to distribute electricity efficiently over long distances, overcoming

9025-754: Was used in 1883 for the Metropolitan Railway station lighting in London , while the single-phase 1884 system in Turin , Italy, was the first multiple-user AC distribution system in the world. The Ames Hydroelectric Generating Plant , constructed in 1890, was among the first hydroelectric alternating current power plants. A long distance transmission of single-phase electricity from a hydroelectric generating plant in Oregon at Willamette Falls sent power fourteen miles downriver to downtown Portland for street lighting in 1890. In 1891, another transmission system

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