Ham Radio General Class Practice Test

What is meant by flat-topping of a single-sideband phone transmission?

1. Signal distortion caused by insufficient collector current

2. The transmitter's automatic level control is properly adjusted

3. Signal distortion caused by excessive drive

4. The transmitter's carrier is properly suppressed

The correct answer is: Signal distortion caused by excessive drive

Flat-topping refers to a specific type of signal distortion that occurs in a single-sideband (SSB) phone transmission when the modulation exceeds the linear operating range of the transmitter. This is characterized by the waveform of the audio signal becoming "flat" at the peaks, which leads to loss of fidelity and introduces unwanted harmonics into the signal. In the context of option C, when excessive drive is applied to the transmitter, it forces the output signal beyond its intended amplitude level. This causes the peaks of the audio waveform to flatten out, resulting in distortion that compromises the quality of the transmitted signal. Flat-topping can impact not only the sound quality for listeners but also the signal's effectiveness over long distances due to the introduction of spurious emissions. The other options refer to different phenomena: the insufficient collector current is more about the circuitry being underused and doesn't specifically relate to modulation levels; proper adjustment of the automatic level control (ALC) helps manage output levels but is not the sole cause of flat-topping; and while proper suppression of the carrier is important in SSB transmission, it does not address the distortion caused by excessive drive. Therefore, recognizing that excessive drive leads to signal distortion is crucial in understanding flat-topping and maintaining transmission quality