Read the following statements regarding different modulation techniques: 1. In Amplitude Modulation (AM), the bandwidth of the modulated signal is twice the modulating signal frequency. 2. Frequency Modulation (FM) typically consumes less power than AM for the same coverage area. 3. Phase Modulation (PM) is equivalent to Frequency Modulation (FM) when the modulating signal is integrated before applying to the phase modulator. Which of the above statements are correct?
1 and 3 only
Statement 1 is correct: an AM wave contains the carrier fc and two sidebands at fc + fm and fc − fm, so its bandwidth is 2fm, i.e. twice the modulating signal frequency.
Statement 2 is incorrect: FM is broadcast at VHF frequencies that travel by line-of-sight (space wave), so covering the same large area as medium-wave AM (which travels as a ground wave) needs more transmitters or more radiated power. FM's real advantages are better noise immunity and fidelity, not lower power for the same coverage.
Statement 3 is correct: in FM the frequency deviation is proportional to the message, while in PM the phase deviation is proportional to it. Since frequency is the rate of change of phase, integrating the message first and then feeding it to a phase modulator produces an FM wave. This is the indirect (Armstrong) method of generating FM.
Hence, statements 1 and 3 only are correct.
Important Questions from Electromagnetic Waves
The radio waves used for signaling and communication can be classified as which of the following?
- An electromagnetic wave propagates through a transparent, non-magnetic medium. If the relative permittivity of this medium is $\epsilon_r = 4$, and its relative permeability is $\mu_r = 1$, what is the speed of the electromagnetic wave in this medium? (Assume the speed of light in vacuum is $c = 3 \times 10^8$ m/s).
X-rays are produced when a target of suitable material element of high atomic mass is bombarded by a beam of fast moving and high energy particles such as:
Which of the following rays are used in doing LASIK (Laser - Assisted in Situ keratomileusis) eye surgery?
A positively charged particle is placed at the origin (with zero initial velocity) in the presence of a constant electric and a constant magnetic field along the positive z and x directions, respectively. At large times, the overall motion of the particle is adrift along the
