Rectifier/LPF

2. Delayed AGC

Mechanism: Delayed AGC introduces a threshold voltage. The AGC action (gain reduction) only begins when the input signal strength exceeds a predetermined level. For signals below this threshold, the receiver operates at its maximum gain.
Operation: A diode or other threshold device is incorporated into the AGC circuit. This diode is reverse-biased by a fixed voltage. The AGC voltage generated by the detector must overcome this reverse bias before it can affect the gain of the amplifier stages. This ensures that weak signals receive full amplification.
Advantages: Maximizes sensitivity for weak signals, as the gain is not reduced until the signal is strong enough. This is particularly useful for distant stations.

3. Amplified AGC

Mechanism: In situations where a stronger and faster-acting AGC voltage is required, an additional transistor or amplifier stage is used to amplify the rectified AGC voltage before it is applied to control the gain.
Advantages: Provides a more effective and responsive AGC action, suitable for receivers operating in environments with rapidly changing signal strengths.

⭐ TOPIC 9 — AM TRANSMITTER / HIGH LEVEL MODULATION

An AM (Amplitude Modulation) transmitter is an electronic system that modulates a high-frequency carrier wave with an audio frequency (AF) message signal, amplifies the modulated signal, and then transmits it via an antenna. High-level modulation refers to performing the modulation process at a high power level, typically in the final RF amplifier stage.

Block Diagram

Microphone $\rightarrow$ AF amplifier $\rightarrow$ Modulator $\rightarrow$ RF Oscillator $\rightarrow$ Buffer Amplifier $\rightarrow$ Driver Amplifier $\rightarrow$ Power Amplifier (modulated by AF) $\rightarrow$ Antenna