Question
Why is automatic level control (ALC) used with an RF power amplifier?
Answer Options
- A) To balance the transmitter audio frequency response
- B) To reduce harmonic radiation
- C) To prevent excessive drive
- D) To increase overall efficiency
Correct Answer: C
Explanation
Automatic Level Control (ALC) is a negative feedback circuit used primarily in linear RF power amplifiers (required for modes like SSB) to maintain signal quality. The primary function of ALC is to prevent excessive drive to the final amplifier stage.
When the input signal peaks too high (such as during a voice peak), the ALC circuit senses the overdriven condition and reduces the gain in the earlier stages (like the microphone amplifier). This prevents the final amplifier from entering saturation, which would cause ‘flat-topping,’ distortion, and the generation of spurious signals (splatter) outside the desired bandwidth.
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