1.

A speech  signal of 3kHz is used to modulate a carrier signal of frequency 1MHz using amplitude modulation. The frequencies of the side bands will be

Answer»

  Key concept: The process of changing the amplitude of a carrier wave in accordance with the amplitude of the audio frequency (AF) signal is known as amplitude modulation (AM).
In AM, frequency of the carrier wave remains unchanged.
Side band frequencies: The AM wave contains three frequencies fc, (fc + fm) and (fc -fm),fc is called carrier frequency, (fc +fm) and (fc -fm) are called side band frequencies.
(fc +fm): Upper side band (USB) frequency
(fc -fm): Lower side band (LSB) frequency
Side band frequencies are generally close to the carrier frequency.
According to the problem, frequency of carrier signal is fc = 1 MHz and frequency of speech signal = 3 kHz
= 3 x 10-3 MHz
= 0.003 MHz
We know that, Frequencies of side bands = (fc ± fm) = (1 + 0.003) and (1 – 0.003)
So, side band frequencies are 1.003 MHz and 0.997 MHz.  


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