# Analog Communications Questions and Answers – Channel

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This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Channel”.

1. Notch is a ________
a) High pass filter
b) Low pass filter
c) Band stop filter
d) Band pass filter

Explanation: Notch filter is a band stop filter that allows most frequencies to pass through it, except frequencies in a specific range. It is just opposite of a band-pass filter. High pass filter allows higher frequencies to pass while Low pass filter allows lower frequencies to pass through it.

2. Sin wave is ________
a) Aperiodic Signal
b) Periodic Signal
c) Random Signal
d) Deterministic Signal

Explanation: Periodic signal is that which repeats itself after a regular interval. Sin wave is a periodic function since it’s value can be determined at any point of time, as it repeats itself at a regular interval. Aperiodic Signal does not repeat itself at regular interval of time. Random signals are the signals which have uncertain values at any time. While Deterministic signals are the signals which are constant over a period of time.

3. What is the role of channel in communication system?
a) acts as a medium to send message signals from transmitter to receiver
b) converts one form of signal to other
c) allows mixing of signals
d) helps to extract original signal from incoming signal

Explanation: Channel acts as a medium to transmit message signal from source transmitter to the destination receiver. Transducer converts a signal from one form of energy to other. Mixer allows mixing of signals while Demodulator helps to extract original message signal from incoming signal.
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4. Sum of a periodic and aperiodic signal always be an aperiodic signal.
a) True
b) False

Explanation: Periodic signal is a signal which repeats itself after a regular interval. While Aperiodic Signal does not repeat itself at regular interval of time.
For example: Let f(x) = sin(x), be a periodic function with period 2π and g(x) = −sin(x) + sin(√2x), be an aperiodic function. Now the sum of both i.e. f(x) + g(x) = sin(√2x), which is a periodic function.
Therefore, the sum of a periodic and aperiodic signal can be periodic.

5. Noise is added to a signal ________
a) In the channel
b) At receiving antenna
c) At transmitting antenna
d) During regeneration of information

Explanation: Noise is an unwanted signal that gets mixed with the transmitted signal while passing through the channel. The noise interferes with the signal and provides distortion in received signal. The transmitting antenna transmits modulated message signal while the receiving antenna receives the transmitted signal. Regeneration of information refers to demodulating the received signal to produce the original message signal.
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6. Agreement between communication devices are called ________
a) Transmission medium
b) Channel
c) Protocol
d) Modem

Explanation: Protocol is a set of rules that looks after data communication, by acting as an agreement between communication devices. Channel is the transmission medium or the path through which information travels. Modem is a device that modulates and demodulates data.

7. What is the advantage of superheterodyning?
a) High selectivity and sensitivity
b) Low Bandwidth
d) Low fidelity

Explanation: The main advantage of superheterodyning is that it provides high selectivity and sensitivity. It’s bandwidth remains same. It has high adjacent channel rejection and high fidelity.

8. Low frequency noise is ________
a) Flicker noise
b) Shot noise
c) Thermal noise
d) Partition Noise

Explanation: Flicker noise is a type of electronic noise which is generated due to fluctuations in the density of carrier. It’s also known as 1/f as it’s power spectral density increases with a decrease in frequency or increase in offset from a signal.

9. Relationship between amplitude and frequency is represented by ________
a) Time-domain plot
b) Phase-domain plot
c) Frequency-domain plot
d) Amplitude-domain plot

Explanation: Relationship between amplitude and frequency is represented by a frequency-domain plot. Also, it represents the relation between phase and frequency. While a time-domain plot shows how a signal varies over time.

10. A function f(x) is even, when?
a) f(x) = -f(x)
b) f(x) = f(-x)
c) f(x) = -f(x)f(-x)
d) f(x) = f(x)f(-x)

Explanation: Geometrically a function f(x) is even, if plot of the function is symmetric over y-axis. Algebraically, for any function f(x) to be even, f(x) = f(-x).
While for a function f(x) to be odd, f(x) = -f(-x).

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