Question
What is a common cause of overmodulation of AFSK signals?
Answer Options
- A) Excessive numbers of retries
- B) Excessive frequency deviation
- C) Bit errors in the modem
- D) Excessive transmit audio levels
Correct Answer: D
Explanation
AFSK (Audio Frequency-Shift Keying) is a digital mode achieved by injecting audio tones (the two shifted frequencies) into the microphone input of a Single-Sideband (\text{SSB}) transceiver. The \text{SSB} transmitter is then responsible for amplifying and transmitting this audio signal as an \text{SSB} signal on the \text{RF} carrier.
Overmodulation in \text{AFSK} refers to driving the \text{SSB} transmitter beyond its linear operating range, causing clipping and distortion (splatter). The common cause of this is excessive transmit audio levels. If the audio tones injected into the microphone input are too loud, the \text{SSB} final amplifier will clip the signal peaks, generating wideband distortion that causes interference on adjacent frequencies.
This topic was automatically created to facilitate community discussion about this exam question. Feel free to share study tips, memory tricks, or additional explanations!