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Schematic of an AGC used in the analog telephone network; the feedback from output level to gain is effected via a Vactrol resistive opto-isolator.. Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the input.
Note that there is no AGC loop, but simply uses a high-gain IF amplifier which is intentionally driven into saturation (or limiting). For single conversion superheterodyne AM receivers designed for medium wave (AM broadcast) the IF is commonly 455 kHz. Most superheterodyne receivers designed for broadcast FM (88 - 108 MHz) use an IF of 10.7 MHz.
AGC can be compared to the dark adaptation mechanism in the human eye; on entering a dark room the gain of the eye is increased by the iris opening. [20] In its simplest form, an AGC system consists of a rectifier which converts the RF signal to a varying DC level, a lowpass filter to smooth the variations and produce an average level. [21]
A direct-conversion receiver (DCR), also known as a homodyne, synchrodyne, zero intermediate frequency or zero-IF receiver, is a radio receiver design that demodulates the incoming radio signal using synchronous detection driven by a local oscillator whose frequency is identical to, or very close to the carrier frequency of the intended signal.
The Block I AGC initially had 12 kilowords of fixed memory, but this was later increased to 24 kilowords. Block II had 36 kilowords of fixed memory and 2 kilowords of erasable memory. The AGC transferred data to and from memory through the G register in a process called the memory cycle. The memory cycle took 12 timing pulses (11.72 μs).
A block diagram is a diagram of a system in which the principal parts or functions are represented by blocks connected by lines that show the relationships of the blocks. [1] They are heavily used in engineering in hardware design , electronic design , software design , and process flow diagrams .
The block diagram shows the general form of a simple reflex receiver. The receiver functions as a tuned radio frequency (TRF) receiver. The radio frequency (RF) signal from the tuned circuit ( bandpass filter ) is amplified, then passes through the high pass filter to the demodulator , which extracts the audio frequency (AF) ( modulation ...
A 5-tube superheterodyne receiver manufactured by Toshiba circa 1955 Superheterodyne transistor radio circuit circa 1975. A superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency.