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Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to that of the message signal, such as an audio signal .
When modulation is applied to the plate of the final tube, a large audio amplifier is needed for the modulation stage, equal to 1/2 of the DC input power of the modulated stage. Traditionally the modulation is applied using a large audio transformer. However many different circuits have been used for high level AM modulation. See Amplitude ...
Envelope detectors are often a component of other circuits, such as a compressor or an auto-wah or envelope-followed filter. In these circuits, the envelope follower is part of what is known as the " side chain ", a circuit which describes some characteristic of the input, in this case its volume.
A simple crystal radio with no tuned circuit can be used to listen to strong AM broadcast signals. An early form of envelope detector was the crystal detector, which was used in the crystal set radio receiver. A later version using a crystal diode is still used in crystal radio sets today.
DSB-SC is basically an amplitude modulation wave without the carrier, therefore reducing power waste, giving it a 50% efficiency. This is an increase compared to normal AM transmission (DSB) that has a maximum efficiency of 33.333%, since 2/3 of the power is in the carrier which conveys no useful information and both sidebands containing identical copies of the same information.
The mixer circuit can be used not only to shift the frequency of an input signal as in a receiver, but also as a product detector, modulator, phase detector or frequency multiplier. [6] For example, a communications receiver might contain two mixer stages for conversion of the input signal to an intermediate frequency and another mixer employed ...
The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet). Schematic of 4 baud, 8 bit/s data link containing arbitrarily chosen values. A simple example: A telephone line is designed for transferring audible sounds, for example, tones, and not digital bits (zeros and ones). Computers ...
Detectors may be as simple as an "envelope" detector for amplitude modulation, or may be more complex circuits for more recently developed techniques such as frequency-hopping spread spectrum. While not fundamental to a receiver, automatic gain control is a great convenience to the user, since it automatically compensates for changing received ...