Modern Physics 7 Question 20

21. An amplitude modulates signal is given by v(t)=10[1+0.3cos(2.2×104t)]sin(5.5×105t).

Here, t is in seconds. The sideband frequencies (in kHz) are Take, π=227

(Main 2019, 11 Jan I)

(a) 892.5 and 857.5

(c) 178.5 and 171.5

(b) 89.25 and 85.75

(d) 1785 and 1715

Show Answer

Solution:

  1. v(t)=10[1+0.3cos(2.2×104t)][sin(5.5×105t)]

Upper band angular frequency

ων=(2.2×104+5.5×105)rad/s=572×103rad/s

Similarly, lower band angular frequency.

ωL=(5.5×1052.2×104)rad/s=528×103rad/s

Side band frequency are,

fu=ωu2π=5722πkHz91kHz and fL=ωL2π=5282πkHz84kHz



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