Communication Systems - Study Mode

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[#66] If m t is modulation index of FM. What is the value of ratio $$frac{{{{left( {frac{{ ext{S}}}{{ ext{N}}}}
ight)}_{{ ext{WBFM}}}}}}{{{{left( {frac{{ ext{S}}}{{ ext{N}}}}
ight)}_{{ ext{AM}}}}}}$$ xa0 for 100% amplitude modulation with identical total transmitted power?

(A) $$frac{9}{2}{ ext{m}}_{ ext{f}}^2$$

(B) $$frac{3}{2}{ ext{m}}_{ ext{f}}^2$$

(C) $$frac{3}{2}{ ext{m}}_{ ext{f}}^3$$

(D) $$frac{9}{2}{ ext{m}}_{ ext{f}}^3$$

Correct Answer

(A) $$frac{9}{2}{ ext{m}}_{ ext{f}}^2$$

[#67] Which is not true about frequency deviation in PM

(A) ∆f decreases with f m increasing

(B) ∆f independent of f m

(C) ∆f increases with f m increasing

(D) ∆f increases with f m decreasing

Correct Answer

(C) ∆f increases with f m increasing

[#68] An amplitude modulated amplifier has a radio frequency output of 50 W at 100% modulation. The internal loss in the modulator is 10 W. The unmodulated carrier power is

(A) 40 W

(B) 50 W

(C) 60 W

(D) 80 W

Correct Answer

(A) 40 W

[#69] What is the assigned bandwidth of each of the channels in the AM broadcast band?

(A) 5 kHz

(B) 15 kHz

(C) 10 kHz

(D) 200 kHz

Correct Answer

(C) 10 kHz

[#70] A carrier wave is phase modulated with frequency deviation of 20 kHz by a single tone frequency of 2 kHz. If the single tone frequency is increased to 2 kHz, assuming that phase deviation remains unchanged, bandwidth of the PM signal is

(A) 20 kHz

(B) 32 kHz

(C) 22 kHz

(D) 44 kHz

Correct Answer

(D) 44 kHz