Question
What is the highest modulation index permitted at the highest modulation frequency for angle modulation below 29.0 MHz?
Answer Options
- A) 0.5
- B) 1.0
- C) 2.0
- D) 3.0
Correct Answer: B
Explanation
Angle modulation (which includes both Frequency Modulation, FM, and Phase Modulation, PM) is generally permitted in certain segments below 29.0 MHz, but the bandwidth is strictly controlled to conserve spectrum on the HF bands. The degree of modulation for angle-modulated signals is quantified by the modulation index, which is the ratio of frequency deviation to the modulating frequency.
To limit the occupied bandwidth of angle-modulated signals on the HF bands, the FCC places a restriction on the modulation index. The highest modulation index permitted at the highest modulation frequency for angle modulation below 29.0 MHz is 1.0. This is a strict control measure to ensure that the transmitted signal does not become unnecessarily wide, which could cause interference to adjacent users.
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