on-off keying

Amplitude-shift keying (ASK) is a form of modulation which represents digital data as variations in the amplitude of a carrier wave. Amplitude-shift keying - Encoding. The simplest and most common form of ASK operates as a switch, using the presence of a carrier wave to indicate a binary one and its absence to indicate a binary zero. This type of modulation is called on-off keying, and is used at radio frequencies to transmit Morse code (referred to as continuous wave operation). More s ...

Including:

• Amplitude-shift keying - Encoding
• Amplitude-shift keying - Probability of error
• Amplitude-shift keying - Considerations

Read more here: » Amplitude-shift keying: Encyclopedia - Amplitude-shift keying

Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal. (Contrast this with frequency modulation, in which the frequency of the carrier is varied; and phase modulation, in which the phase is varied.) AM is commonly used at radio frequencies and was the first method used to broadcast commercial radio. The term "AM" is sometimes used generically to refer to the AM broadcast (mediumwave) band (see AM radio). Ampli ...

Including:

• Amplitude modulation - Applications in radio
• Amplitude modulation - AM vs. FM
• Amplitude modulation - Forms of AM
• Amplitude modulation - Example
• Amplitude modulation - A more general example
• Amplitude modulation - Modulation index
• Amplitude modulation - Amplitude modulator designs
• Amplitude modulation - Circuits
• Amplitude modulation - Low level
• Amplitude modulation - High level

Read more here: » Amplitude modulation: Encyclopedia - Amplitude modulation

Very early radio transmitters used a spark gap to produce radio-frequency oscillations in the transmitting antenna; these signals had a characteristic rapidly damped amplitude during each pulse of radiated energy. When alternators and later electronic oscillators became available, the signal strength remained constant during each code element, leading to the description of this technique as "continuous" waves. An unmodulated carrier has no bandwidth and conveys no information; the act of keying the carrier on and off produces a finite ...

See also:

Continuous wave, Continuous wave - Radio, Continuous wave - Key clicks, Continuous wave - Laser physics

Read more here: » Continuous wave: Encyclopedia II - Continuous wave - Radio

The simplest and most common form of ASK operates as a switch, using the presence of a carrier wave to indicate a binary one and its absence to indicate a binary zero. This type of modulation is called on-off keying, and is used at radio frequencies to transmit Morse code (referred to as continuous wave operation). More sophisticated encoding schemes have been developed which represent data in groups using additional amplitude levels. For instance, a four-level encoding scheme can represent two bits with each shift in amplitude ...

See also:

Amplitude-shift keying, Amplitude-shift keying - Encoding, Amplitude-shift keying - Probability of error, Amplitude-shift keying - Considerations

Read more here: » Amplitude-shift keying: Encyclopedia II - Amplitude-shift keying - Encoding

Suppose we wish to modulate a simple sine wave on a carrier wave. The equation for the carrier wave of frequency ωc, taking its phase to be a reference phase of zero, is c(t) = Csin(ωct). The equation for the simple sine wave of frequency ωm (the signal we wish to broadcast) is m(t) = Msin(ω ...

See also:

Amplitude modulation, Amplitude modulation - Applications in radio, Amplitude modulation - AM vs. FM, Amplitude modulation - Forms of AM, Amplitude modulation - Example, Amplitude modulation - A more general example, Amplitude modulation - Modulation index, Amplitude modulation - Amplitude modulator designs, Amplitude modulation - Circuits, Amplitude modulation - Low level, Amplitude modulation - High level

Read more here: » Amplitude modulation: Encyclopedia II - Amplitude modulation - Example

Any form of digital modulation necessarily uses a finite number of distinct signals to represent digital data. In the case of PSK, a finite number of phases are used. In the case of FSK, a finite number of frequencies are used. In the case of ASK, a finite number of amplitudes are used. This is very similar to pulse code modulation 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 th ...

See also:

Modulation, Modulation - Analog modulation techniques, Modulation - Digital modulation techniques, Modulation - Pulse modulation, Modulation - Miscellaneous techniques

Read more here: » Modulation: Encyclopedia II - Modulation - Digital modulation techniques

The invention of the device is credited to David Edward Hughes, among others. Oliver Joseph Lodge, in his Royal Institute lectures ("The Work of Hertz and Some of His Successors") coined the term "coherer" and gained the "syntonic" (or tuning) patent from the United States Patent Office. In 1892, Edouard Branly invented a coherer (which was named after him). Also, Alexander Popov developed a device similar to the "Branly coherer" to ...

See also:

Coherer, Coherer - History, Coherer - Description

Read more here: » Coherer: Encyclopedia II - Coherer - History

As with other modulation indices, in AM, this quantity, also called modulation depth, indicates by how much the modulated variable varies around its 'original' level. For AM, it relates to the variations in the carrier amplitude and is defined as: . So if h = 0.5, the carrier amplitude varies by 50% above and below its unmodulated level, and for h = 1.0 it varies by 100%. Modulation depth greater than 100% is generally to be avoided - practical transmitter systems will usually incorporate some ...

See also:

Amplitude modulation, Amplitude modulation - Applications in radio, Amplitude modulation - AM vs. FM, Amplitude modulation - Forms of AM, Amplitude modulation - Example, Amplitude modulation - A more general example, Amplitude modulation - Modulation index, Amplitude modulation - Amplitude modulator designs, Amplitude modulation - Circuits, Amplitude modulation - Low level, Amplitude modulation - High level

Read more here: » Amplitude modulation: Encyclopedia II - Amplitude modulation - Modulation index

ASK is the simplest kind of modulation that can be used to send data through a channel. It has several bad points: it can be used only when the signal-to-noise ratio is very high, because most of the signal is transmitted at reduced power, so it would be hard to recover. it needs A/D converters working at a frequency that could be higher than necessary: for example, if the bandwidth between 100 and 101 MHz is used for the transmission, the spectrum of the signal will be only 1 MHz wide, but the A/D converter will need to work at 101*2 = 202 MHz. In QAM modulation, ...

See also:

Amplitude-shift keying, Amplitude-shift keying - Encoding, Amplitude-shift keying - Probability of error, Amplitude-shift keying - Considerations

Read more here: » Amplitude-shift keying: Encyclopedia II - Amplitude-shift keying - Considerations

A basic AM radio transmitter works by first DC-shifting the modulating signal, then multiplying it with the carrier wave using a frequency mixer. The output of this process is a signal with the same frequency as the carrier but with peaks and troughs that vary in proportion to the strength of the modulating signal. This is amplified and fed to an antenna. Amplitude modulation - AM vs. FM. AM radio's main limitation is its susceptibility to atmospheric interference, which is heard as static from the receive ...

See also:

Amplitude modulation, Amplitude modulation - Applications in radio, Amplitude modulation - AM vs. FM, Amplitude modulation - Forms of AM, Amplitude modulation - Example, Amplitude modulation - A more general example, Amplitude modulation - Modulation index, Amplitude modulation - Amplitude modulator designs, Amplitude modulation - Circuits, Amplitude modulation - Low level, Amplitude modulation - High level

Read more here: » Amplitude modulation: Encyclopedia II - Amplitude modulation - Applications in radio

In its basic form, amplitude modulation produces a signal with power concentrated at the carrier frequency and in two adjacent sidebands. Each sideband is equal in bandwidth to that of the modulating signal and is a mirror image of the other. Thus, most of the power output by an AM transmitter is effectively wasted: half the power is concentrated at the carrier frequency, which carries no useful information (beyond the fact that a signal is present); the remaining power is split between t ...

See also:

Amplitude modulation, Amplitude modulation - Applications in radio, Amplitude modulation - AM vs. FM, Amplitude modulation - Forms of AM, Amplitude modulation - Example, Amplitude modulation - A more general example, Amplitude modulation - Modulation index, Amplitude modulation - Amplitude modulator designs, Amplitude modulation - Circuits, Amplitude modulation - Low level, Amplitude modulation - High level

Read more here: » Amplitude modulation: Encyclopedia II - Amplitude modulation - Forms of AM

Amplitude modulation - Circuits. A wide range of different circuits have been used for AM, but one of the simplest circuits uses anode or collector modulation applied via a transformer. While it is perfectly possible to create good designs using solid-state electronics, valved (tube) circuits are shown here. In general, valves are able to easily yield RF powers far in excess of what can be achieved using solid state. Most high-power broadcast stations still use valves. Modulation circuit designs can be broadly divided into low and high l ...

See also:

Amplitude modulation, Amplitude modulation - Applications in radio, Amplitude modulation - AM vs. FM, Amplitude modulation - Forms of AM, Amplitude modulation - Example, Amplitude modulation - A more general example, Amplitude modulation - Modulation index, Amplitude modulation - Amplitude modulator designs, Amplitude modulation - Circuits, Amplitude modulation - Low level, Amplitude modulation - High level

Read more here: » Amplitude modulation: Encyclopedia II - Amplitude modulation - Amplitude modulator designs