Answer Key

1. The three basic parts of a communication system are the Sender, Channel, and Receiver. The Sender is the person or station that transmits a message, the Channel is the medium through which the signal travels, and the Receiver is the person or station that receives the message.
2. Modulation is the process of changing the parameters of a high-frequency carrier signal in accordance with the instantaneous values of a message signal. Its purpose is to increase the strength of the baseband message signal, allowing it to travel longer distances without distortion and enabling the use of smaller, more practical antennas.
3. An analog signal is a continuous time-varying signal that represents a time-varying quantity, such as the gradual filling of a water tank. A digital signal is discrete and non-continuous, representing individual values like binary 1s and 0s or the daily attendance of students in a class.
4. Noise is an unwanted signal that interferes with the original message signal, corrupting its parameters. Two primary effects of noise are that it limits the operating range of systems by affecting the weakest signal that can be processed, and it negatively affects the sensitivity of receivers, which is their ability to process a minimum input signal for a quality output.
5. The Sampling Theorem states that a signal can be exactly reproduced if it is sampled at a rate (fs) greater than or equal to twice its maximum frequency (W). This minimum sampling rate (fs = 2W) is called the Nyquist rate. Sampling below the Nyquist rate causes Aliasing, where high-frequency components overlap and distort the signal, leading to information loss.
6. The Modulation Index states the level of modulation a carrier wave undergoes. Under-modulation occurs when the index is less than 1, resulting in an inefficient but clean signal. Over-modulation occurs when the index is greater than 1, causing the carrier to experience a 180-degree phase reversal, which distorts the wave and creates interference.
7. Multiplexing is the process of combining multiple signals into one signal over a shared medium. In Frequency Division Multiplexing (FDM), signals are combined by assigning each to a different frequency. In Time Division Multiplexing (TDM), a time frame is divided into slots, with each signal being allotted a specific time slot for transmission.
8. The key difference is which parameter of the carrier signal is varied. In Frequency Modulation (FM), the frequency of the carrier signal varies in accordance with the instantaneous amplitude of the message signal. In Phase Modulation (PM), the phase of the carrier signal is varied in accordance with the message signal’s instantaneous amplitude.
9. Spread Spectrum Modulation is a class of signaling techniques that spreads a signal over a wide frequency band to provide secure communication that is resistant to interference and jamming. The two main classifications are Frequency Hopped Spread Spectrum (FHSS), where users change frequencies at specified intervals, and Direct Sequence Spread Spectrum (DSSS), where data is multiplied by a secret “chipping code.”
10. Total Internal Reflection is a phenomenon where a light ray is completely reflected back into its original medium when the angle of incidence is greater than the critical angle. Optical fibers use this principle with a core (n1) and cladding (n2) where n1 > n2; light signals sent down the core repeatedly strike the core-cladding boundary at an angle greater than the critical angle, causing them to be totally reflected and guided along the fiber.

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