BasicB-003-011-007

You are transmitting using amplitude modulation. What bandwidth does your signal occupy if the highest frequency of your voice is 3 kHz?

B
Answer
Basic radio theory
Type
A
9 kHz
B
6 kHz
C
3 kHz
D
12 kHz

Answer Notes

Standard Amplitude Modulation (AM) creates a signal that includes both an Upper Sideband (USB) and a Lower Sideband (LSB). Each of these sidebands occupies an amount of spectrum equal to the highest frequency of the modulating audio signal. Since the highest frequency of the voice in this example is 3 kHz, each sideband will be 3 kHz wide. To find the total bandwidth, you add the width of both sidebands together (3 kHz + 3 kHz), which results in a total bandwidth of 6 kHz. Options like 3 kHz are incorrect because that would only account for a single sideband (SSB), while 9 kHz and 12 kHz simply do not follow the mathematical rule that standard AM bandwidth is exactly twice the modulating frequency.
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What frequency components are present in the bandwidth of an amplitude modulated signal?