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erece
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What is the purpose of delayed automatic gain controller (AGC) in communication receiver ?
See figure 1 in this paper.erece said:What is the purpose of delayed automatic gain controller (AGC) in communication receiver ?
I believe the AGC is needed at all input signal levels to maintain a constant audio output signal level.skeptic2 said:Bob, I still don't agree. The only reference to delayed AGC in your reference is in the second sentence on page VI which says, "AGC systems that include a reference voltage inside the control loop are referred as delayed AGC." Unless I am missing something, I don't believe the addition of a reference voltage will cause a time delay in the AGC action. Its purpose is to disable the AGC at low signal levels.
The AGC signal control voltage is supposed to be an average over a second or two. Causality requires that averaging produces a delay. Anything faster than this will distort the audio signal. This is why there is an RC low-pass filter in the feedback loop. Too much gain in the feedback loop will make it unstable.I am not aware of any AGC systems in which a time delayed AGC is desired. True, in AM, SSB or QAM, the desired amplitude modulation needs to be filtered out of the AGC and that results in some time delay, but the delay introduced by the filtering is not desired. Time delayed AGC results in overshoot and if severe enough, oscillation.
Bob S said:The AGC signal control voltage is supposed to be an average over a second or two. Causality requires that averaging produces a delay. Anything faster than this will distort the audio signal. This is why there is an RC low-pass filter in the feedback loop. Too much gain in the feedback loop will make it unstable.
Bob S
AGC stands for Automatic Gain Control, which is a feature in communication receivers that automatically adjusts the gain or amplification of the received signal to maintain a constant output level. This helps to achieve a consistent and clear signal, even in situations where the received signal may be weak or fluctuating.
AGC works by continuously monitoring the strength of the received signal and adjusting the gain or amplification accordingly. When the received signal is weak, the AGC increases the gain to amplify the signal. Conversely, when the received signal is strong, the AGC decreases the gain to prevent overloading and distortion.
AGC offers several benefits, including improved signal quality, reduced interference, and increased dynamic range. It also helps to protect the receiver from damage due to overloading. Additionally, AGC allows for a more efficient use of the receiver's amplification capabilities, resulting in better overall performance.
One potential drawback of AGC is that it can introduce some delay in the signal, which may affect real-time communication. Additionally, if the AGC is not properly calibrated or the received signal is too weak, it may cause the receiver to amplify background noise or unwanted signals.
Yes, most communication receivers have the option to turn off AGC. This can be useful in situations where a constant gain is desired, such as when working with strong and stable signals. However, turning off AGC may result in a less clear or distorted signal in situations where the received signal is weak or fluctuating.