Sarthaks Test
+1 vote
in Physics by (38.1k points)

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

(a) 1.003 MHz and 0.997 MHz. 

(b) 3001 kHz and 2997 kHz. 

(c) 1003 kHz and 1000 kHz. 

(d) 1 MHz and 0.997 MHz.

2 Answers

+1 vote
by (257k points)
Best 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.

+1 vote
by (63.6k points)

(a) 1.003 MHz and 0.997 MHz.

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