ARRL Technician Practice Exam

What happens when the deviation of an FM transmitter is increased?

1. The audio quality improves

2. Its signal occupies more bandwidth

3. The frequency range decreases

4. The power output increases

The correct answer is: Its signal occupies more bandwidth

When the deviation of an FM transmitter is increased, the signal occupies more bandwidth. This is due to the nature of frequency modulation, where the carrier frequency shifts based on the amplitude of the incoming audio signal. According to Carson's Rule, the total bandwidth of an FM signal can be approximated as twice the sum of the deviation and the highest frequency of the modulating signal. Thus, as the deviation increases, the total bandwidth required for the transmission also increases. Greater deviation means that the frequency of the transmitted signal varies more widely, resulting in a broader spectrum used for broadcasting. This increase in bandwidth is necessary to accommodate the wider swings in frequency caused by the audio signals being transmitted. It is important in practical terms, as using excessive deviation could lead to interference with nearby channels. Other options do not accurately address the consequences of increased deviation in FM transmission. While audio quality may improve with proper deviation settings, this is not guaranteed and heavily depends on other factors like the modulation index. Likewise, increasing deviation does not lead to a decrease in frequency range or an increase in power output; these are unrelated characteristics of the transmitter operation.