Question
What is meant by the term “flat-topping,” when referring to an amplitude-modulated phone signal?
Answer Options
- A) Signal distortion caused by insufficient collector current
- B) The transmitter’s automatic level control (ALC) is properly adjusted
- C) Signal distortion caused by excessive drive or speech levels
- D) The transmitter’s carrier is properly suppressed
Correct Answer: C
Explanation
Flat-topping is a form of severe non-linear distortion that occurs in Amplitude Modulation (AM) and Single Sideband (SSB) transmitters. It is caused by excessive drive or speech levels that push the amplifier beyond its linear operating range.
When the input audio signal is too high, the final amplifier attempts to exceed its maximum possible peak power output, which results in the clipping (flattening) of the peaks of the RF modulation envelope. This clipping is highly non-linear, introducing excessive bandwidth (‘splatter’) and making the voice sound harsh and distorted.
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