Question

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) 1003 KHz and 1000 KHz
(BX 1.003 MHz and 0.997 MHz
(C) 1 MHz and 0.997 MHz
(D) 3001 KHz and 2997 KHZMO

Answer 1

Solution :

γ=1MHz

Δγ=3KHz

=0.003Mz

The frequencies of the side band =

(γ+Δγ) and (γ−Δγ)

=(1+0.003)and(1−003)

=1.003and0.997

Answer 2

ANSWER:

The side band frequencies are 1.003 MHz and 0.997 MHz.

EXPLANATION:

   The speech signal frequency is represented as $f_{m}$ and the carrier signal frequency is represented as $f_{c}$. In amplitude modulation, the carrier frequency signal will get amplified based on their speech signal frequency.

   The variation in the resultant frequency using amplitude modulation comes in three types, (i) $f_{C}$ which is the carrier signal itself without any change, (ii) $\left(f_{c}+f_{m}\right)$ and (iii) $\left(f_{c}-f_{m}\right)$ The last two types of resultant frequencies are termed as side bands frequency as upper side band and lower side band frequencies respectively.

Here, the carrier frequency is given as $f_{c}=1 M H z$

The speech frequency is given as $f_{m}=3 \mathrm{KHz}=0.003 \mathrm{MHz}$

So the side band frequencies will be

$\text {Upper side band frequency}=\left(f_{c}+f_{m}\right)=(1+0.003)=1.003 \mathrm{MHz}$

$\text { Lower side band frequency }=\left(f_{c}-f_{m}\right)=(1-0.003)=0.997 M H z$

Thus the side band frequencies are 1.003 MHz and 0.997 MHz.