Question
Why should the ALC system be inactive when transmitting AFSK data signals?
Answer Options
- A) ALC will invert the modulation of the AFSK mode
- B) The ALC action distorts the signal
- C) When using digital modes, too much ALC activity can cause the transmitter to overheat
- D) All these choices are correct
Correct Answer: B
Explanation
Audio Frequency-Shift Keying (AFSK) involves generating a digital signal using two distinct, constant-amplitude audio tones. These tones are fed into the Single Sideband (SSB) transmitter’s microphone input, where they are converted into an RF signal. Because the tones are of constant amplitude, the resulting RF signal should also be of constant, maximum amplitude.
If the Automatic Level Control (ALC) system detects this constant, high-level input and attempts to reduce it, it will create unnecessary amplitude modulation (clipping) of the constant-amplitude signal. This clipping means the ALC action distorts the signal, introducing unwanted sidebands and interfering with the ability of the receiving station’s modem to decode the data accurately. Therefore, ALC should be kept out of the loop for most data modes.
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