Communication Systems — Practice Quiz

mₐ = vao / vco

Step 1: In AM, the modulated wave is expressed as: v_mod = vco(1 + mₐ sin ωₐt) sin ωct. Step 2: The modulation index mₐ represents the ratio of the amplitude of the modulating (audio) signal to the amplitude of the carrier wave. Step 3: So mₐ = vao / vco, where vao = amplitude of audio (modulating) signal and vco = amplitude of carrier wave. Step 4: This ratio measures the 'depth' of modulation — how much the carrier amplitude is being varied by the audio signal. Step 5: If mₐ > 1, overmodulation occurs causing distortion, so mₐ ≤ 1 is desirable. The option vco/vao is the reciprocal — a common

Optical fibre

Step 1: Total internal reflection (TIR) occurs when light travels from a denser medium (higher refractive index n₁) to a rarer medium (lower refractive index n₂ < n₁) at an angle greater than the critical angle. Step 2: An optical fibre has a central glass core (refractive index n₁) surrounded by a cladding of slightly lower refractive index (n₂). Step 3: Light entering the core strikes the core-cladding interface at angles greater than the critical angle, and TIR keeps the light confined within the core as it travels along the fibre. Step 4: Coaxial cables use electric field confinement betwe

3 MHz – 30 MHz (HF)

Step 1: Recall the different modes of radio wave propagation and their associated frequency ranges. Step 2: Sky wave (ionospheric) propagation involves radio waves being launched upward, reflected by the ionosphere, and returning to distant locations on Earth. Step 3: The ionosphere (specifically the F₂ layer) reflects electromagnetic waves up to approximately 30 MHz. Waves of frequency 3–30 MHz (HF or High Frequency range, also called short waves) are ideal for this. Step 4: MF waves are absorbed by the ionosphere during daytime. VHF and UHF waves pass through the ionosphere and are not refle

Frequency

Step 1: In any modulation technique, one parameter of the high-frequency carrier wave is varied in accordance with the low-frequency modulating (audio) signal. Step 2: In Frequency Modulation (FM): the frequency of the carrier wave varies according to the instantaneous amplitude of the modulating signal, while the amplitude of the carrier wave remains constant. Step 3: When modulating signal amplitude is HIGH → carrier frequency increases. When modulating signal amplitude is LOW → carrier frequency decreases. Step 4: In contrast, Amplitude Modulation (AM) varies the amplitude, and Phase Modula