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Single-sideband Modulation
In radio communications, SINGLE-SIDEBAND MODULATION (SSB) or SINGLE-SIDEBAND SUPPRESSED-CARRIER MODULATION (SSB-SC) is a type of modulation , used to transmit information, an audio signal , by radio waves . It is a refinement of amplitude modulation which uses transmitter power and bandwidth more efficiently. Amplitude modulation produces an output signal that has twice the bandwidth of the original baseband signal. Single-sideband modulation
Single-sideband modulation
avoids this bandwidth doubling, and the power wasted on a carrier, at the cost of increased device complexity and more difficult tuning at the receiver
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Delta-sigma Modulation
DELTA-SIGMA (ΔΣ; or SIGMA-DELTA, ΣΔ) modulation is a method for encoding analog signals into digital signals as found in an analog-to-digital converter (ADC). It is also used to transfer high bit-count low frequency digital signals into lower bit-count higher frequency digital signals as part of the process to convert digital signals into analog as part of a digital-to-analog converter (DAC). In a conventional ADC, an analog signal is integrated, or sampled, with a sampling frequency and subsequently quantized in a multi-level quantizer into a digital signal. This process introduces quantization error noise. The first step in a delta-sigma modulation is delta modulation. In delta modulation the change in the signal (its delta) is encoded, rather than the absolute value. The result is a stream of pulses, as opposed to a stream of numbers as is the case with PCM
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Radio
RADIO is the technology of using radio waves to carry information, such as sound, by systematically modulating properties of electromagnetic energy waves transmitted through space, such as their amplitude , frequency , phase , or pulse width . When radio waves strike an electrical conductor , the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form. Radio
Radio
systems need a transmitter to modulate (change) some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation (which can be frequency modulation or phase modulation ). Radio
Radio
systems also need an antenna to convert electric currents into radio waves , and radio waves into an electric current. An antenna can be used for both transmitting and receiving
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Audio Signal
An AUDIO SIGNAL is a representation of sound , typically as an electrical voltage . Audio signals have frequencies in the audio frequency range of roughly 20 to 20,000 Hz (the limits of human hearing ). Audio signals may be synthesized directly, or may originate at a transducer such as a microphone , musical instrument pickup , phonograph cartridge, or tape head . Loudspeakers or headphones convert an electrical audio signal into sound. Digital representations of audio signals exist in a variety of formats. An AUDIO CHANNEL or AUDIO TRACK is an audio signal communications channel in a storage device , used in operations such as multi-track recording and sound reinforcement . CONTENTS * 1 Signal flow * 2 Parameters * 3 Digital equivalent * 4 See also * 5 References * 6 External links SIGNAL FLOWSignal flow is the path an audio signal will take from source (microphone ) to the speaker or recording device
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Line Code
In telecommunication , a LINE CODE is a code chosen for use within a communications system for transmitting a digital signal down a line. Line coding is often used for digital data transport. Some line codes are DIGITAL BASEBAND MODULATION or DIGITAL BASEBAND TRANSMISSION methods, and these are baseband line codes that are used when the line can carry DC components. Line coding consists of representing the digital signal to be transported, by a waveform that is appropriate for the specific properties of the physical channel (and of the receiving equipment). The pattern of voltage, current or photons used to represent the digital data on a transmission link is called line encoding. The common types of line encoding are unipolar , polar , bipolar , and Manchester encoding
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Pulse-width Modulation
PULSE-WIDTH MODULATION (PWM), or PULSE-DURATION MODULATION (PDM), is a modulation technique used to encode a message into a pulsing signal . Although this modulation technique can be used to encode information for transmission, its main use is to allow the control of the power supplied to electrical devices, especially to inertial loads such as motors. In addition, PWM is one of the two principal algorithms used in photovoltaic solar battery chargers, the other being maximum power point tracking . The average value of voltage (and current ) fed to the load is controlled by turning the switch between supply and load on and off at a fast rate. The longer the switch is on compared to the off periods, the higher the total power supplied to the load. The PWM switching frequency has to be much higher than what would affect the load (the device that uses the power), which is to say that the resultant waveform perceived by the load must be as smooth as possible
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Pulse-code Modulation
PULSE-CODE MODULATION (PCM) is a method used to digitally represent sampled analog signals . It is the standard form of digital audio in computers, compact discs , digital telephony and other digital audio applications. In a PCM stream , the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps. LINEAR PULSE-CODE MODULATION (LPCM) is a specific type of PCM where the quantization levels are linearly uniform. This is in contrast to PCM encodings where quantization levels vary as a function of amplitude (as with the A-law algorithm or the μ-law algorithm ). Though PCM is a more general term, it is often used to describe data encoded as LPCM
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Modem
A MODEM (MOdulator-DEModulator) is a network hardware device that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used with any means of transmitting analog signals, from light emitting diodes to radio . A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data. Modems are generally classified by the maximum amount of data they can send in a given unit of time , usually expressed in bits per second (symbol BIT/S, sometimes abbreviated "bps"), or bytes per second (symbol B/S). Modems can also be classified by their symbol rate , measured in baud
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Angle Modulation
ANGLE MODULATION is a class of carrier modulation that is used in telecommunications transmission systems. The class comprises frequency modulation (FM) and phase modulation (PM), and is respectively based on altering the frequency or the phase of a carrier signal to encode the message signal. This contrasts with varying the amplitude of the carrier, practiced in amplitude modulation (AM) transmission, the earliest of the major modulation methods used widely in early radio broadcasting. CONTENTS * 1 Formalism * 2 Frequency modulation
Frequency modulation
* 3 Phase modulation
Phase modulation
* 4 See also * 5 References FORMALISMIn general form, an analog modulation process of a sinusoidal carrier wave may be described by the following equation: m ( t ) = A ( t ) cos ( t + ( t ) ) {displaystyle m(t)=A(t)cdot cos(omega t+phi (t)),}
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Polar Modulation
POLAR MODULATION is analogous to quadrature modulation in the same way that polar coordinates are analogous to Cartesian coordinates
Cartesian coordinates
. Quadrature modulation makes use of Cartesian coordinates, x and y. When considering quadrature modulation, the x axis is called the I (in-phase) axis, and the y axis is called the Q (quadrature) axis. Polar modulation makes use of polar coordinates, r (amplitude) and Θ (phase). The quadrature modulator approach to digital radio transmission requires a linear RF power amplifier which creates a design conflict between improving power efficiency or maintaining amplifier linearity. Compromising linearity causes degraded signal quality, usually by adjacent channel degradation, which can be a fundamental factor in limiting network performance and capacity
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Transmitter
In electronics and telecommunications a TRANSMITTER or RADIO TRANSMITTER is an electronic device which produces radio waves with an antenna . The transmitter itself generates a radio frequency alternating current , which is applied to the antenna. When excited by this alternating current the antenna radiates radio waves. In addition to their use in broadcasting , transmitters are necessary component parts of many electronic devices that communicate by radio , such as cell phones , wireless computer networks , Bluetooth
Bluetooth
enabled devices, garage door openers , two-way radios in aircraft, ships, spacecraft, radar sets and navigational beacons. The term transmitter is usually limited to equipment that generates radio waves for communication purposes; or radiolocation , such as radar and navigational transmitters
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Radio Wave
RADIO WAVES are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 GHz
GHz
to as low as 3 kHz , though some definitions describe waves above 1 or 3 GHz
GHz
as microwaves , or include waves of any lower frequency. At 300 GHz, the corresponding wavelength is 1 mm (0.039 in), and at 3 kHz is 100 km (62 mi). Like all other electromagnetic waves, they travel at the speed of light . Naturally occurring radio waves are generated by lightning , or by astronomical objects . Artificially generated radio waves are used for fixed and mobile radio communication , broadcasting , radar and other navigation systems, communications satellites , computer networks and innumerable other applications. Radio waves
Radio waves
are generated by radio transmitters and received by radio receivers
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World War I
Allied victory * Central Powers ' victory on the Eastern Front nullified by defeat on the Western Front * Fall of the German , Russian , Ottoman , and Austro-Hungarian empires * Russian Civil War and foundation of Soviet Union
Soviet Union
* Formation of new countries in Europe
Europe
and the Middle East * Transfer of German colonies and regions of the former Ottoman Empire to other powers * Establishment of the League of Nations
League of Nations
. (more..
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Electric Power
ELECTRIC POWER is the rate, per unit time, at which electrical energy is transferred by an electric circuit . The SI unit of power is the watt , one joule per second . Electric power
Electric power
is usually produced by electric generators , but can also be supplied by sources such as electric batteries . It is usually supplied to businesses and homes by the electric power industry through an electric power grid . Electric power
Electric power
is usually sold by the kilowatt hour (3.6 MJ) which is the product of power in kilowatts multiplied by running time in hours. Electric utilities measure power using an electricity meter , which keeps a running total of the electric energy delivered to a customer. Electrical power provides a low entropy form of energy and can be carried long distances and converted into other forms of energy such as motion , light or heat with high energy efficiency
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Spectrum
A SPECTRUM (plural spectra or spectrums ) is a condition that is not limited to a specific set of values but can vary, without steps, across a continuum . The word was first used scientifically in optics to describe the rainbow of colors in visible light after passing through a prism . As scientific understanding of light advanced, it came to apply to the entire electromagnetic spectrum . Spectrum
Spectrum
has since been applied by analogy to topics outside of optics. Thus, one might talk about the "spectrum of political opinion ", or the "spectrum of activity" of a drug, or the "autism spectrum ". In these uses, values within a spectrum may not be associated with precisely quantifiable numbers or definitions. Such uses imply a broad range of conditions or behaviors grouped together and studied under a single title for ease of discussion. Nonscientific uses of the term spectrum are sometimes misleading
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Longwave
In radio, LONGWAVE, LONG WAVE or LONG-WAVE, and commonly abbreviated LW, refers to parts of the radio spectrum with wavelengths longer than what was originally called the medium wave broadcasting band. The term is historic, dating from the early 20th century, when the radio spectrum was considered to consist of longwave (LW), medium wave (MW), and short wave (SW) radio bands. Most modern radio systems and devices use wavelengths which would then have been considered 'ultra-short'. In contemporary usage, the term longwave is not defined precisely, and its precise meaning varies. It may be used for radio wavelengths longer than 1,000 metres, i.e. frequencies up to 300 kilohertz (kHz) including the International Telecommunications Union\'s (ITU's) low frequency (LF) (30–300 kHz) and very low frequency (VLF) (3–30 kHz) bands. Sometimes the upper limit is taken to be higher than 300 kHz, but not above the start of the medium wave band at 520 kHz
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