BasicB-001-019-004
What is the maximum percentage of modulation permitted for amateur radio voice communications?
C
Answer
Regulations and administration
Type
A
75%
B
50%
C
100%
D
90%
Answer Notes
In amplitude modulation (AM) and related voice modes, 100% modulation represents the maximum level where the radio frequency carrier is fully modulated by the audio signal without clipping or distortion.
Exceeding 100% modulation means the carrier is completely cut off during negative audio peaks. This abrupt cutoff creates severe distortion and generates spurious emissions (splatter) that bleed into adjacent radio channels.
Therefore, regulations strictly prohibit modulation exceeding 100%. Lower percentages like 50% or 75% are perfectly legal but result in a quieter signal, whereas 100% is the absolute maximum permitted limit.
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Amateur radio stations are required to have means of indicating or preventing a signal quality problem unique to voice transmissions. What is it?
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What must all amateur radio stations be capable of reliably measuring, regardless of emission mode?