Download Electrical Communication sheet--1

Electrical Communication
Sheet-1
Dr. Waleed M. Gaballah
Q.1 Choose the best answer ..
1- ---------------- process that allows information to pass between a sender and receiver
a) Channel
b) Communication
c) Modulation
d) Multiplexing
2- ---------------- means communication by electrical or electromagnetic means, usually
over a distance
a) Communication
b) Modulation
c) Telecommunication d) Transducing
3- ---------------- converts the message produced by a source to a form suitable for the
communication system.
a) Modulator
b) transducer
c) antenna
d) encoder
4- The TV communication is a --------------- communication system
a) Simplex
b) Half duplex
c) Full Duplex
d) None of the above
5- Twisted pairs are used extensively in ----------------.
a) TV cables
b) Link between switching centers
c) LAN networks
d) All the above
6- The transmission channel is the ------------- that bridges the distance from source to
destination.
a) Filter
b) Transmitter
c) Noise
d) medium
7- The ------------ plot shows changes in signal amplitude with respect to time.
a) Frequency domain
b) Time domain
c) Power gain
d) Spectrum
8- Any composite signal is actually a combination of simple sine waves with different ------------------.
a) amplitudes
b) Frequencies
c) Phases
d) All of the above
9- Simultaneous transmission of many signals by sharing the transmission time is
called --------------------.
a) AM
b) FM
c) TDM
d) FDM
10- Simultaneous transmission of many signals by sharing the bandwidth of the
communication channel is called --------------------.
a) AM
b) FM
c) TDM
d) FDM
11- Your home telephone is directly connected to the local exchange by ---------------cable.
a) Twisted pair
b) Coaxial Cable
c) SMF
d) MMF
12- Optical fibers are made up of ………
a) Plastic
b) glass
c) silica
d) all of the above
13- FM stands for ________
a) Frequency Modulation
b) Frequency Modulator
c) Frequency Multiplier
d) Frequency Mixer
14- Why a sinusoidal signal is considered analog?
a) It moves in both positive and negative direction
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b) It is positive for one half cycle
c) It is negative for one half cycle
d) It has infinite number of amplitudes in the range of values of the independent
variable
15- What do you understand by the term analog communication?
a) A method in which one of the properties of a carrier signal varies in proportion
to an instantaneous value of modulation signal
b) A way for data and computer communication
c) A numerical coded communication
d) A suitable method for long distance communication
16- What is Demodulation?
a) Process of varying one or more properties of a periodic waveform
b) Recovering information from modulated signal
c) Process of mixing a signal with a sinusoid to produce a new signal
d) Involvement of noise
17- Medium which sends information from source to receiver is called ________
a) Transmitter
b) Transducer
c) Loudspeaker
d) Channel
18- Telephones send information through wires in form of ________
a) radio signals
b) electrical signal
c) electromagnetic waves
d) microwaves
19- Cell phones sent information in form of ________
a) microwaves
b) electrical signals
c) infrared Waves
d) radio waves
20- Modulation is done in ________
a) Receiver
b) Transducer
c) Between transmitter and radio receiver
d) Transmitter
21- What is the role of transmitter in communication system?
a) to decode a signal to be transmitted
b) to convert one form of energy into other
c) to detect and amplify information signal from the carrier
d) to produce radio waves to transmit data
22- Demodulation is done in ________
a) Channel
b) Receiver
c) Receiving antenna
d) Transducer
23- Process of recovering information signal from received carrier is known as _______
a) Sensitivity
b) Selectivity
c) Demodulation
d) Fidelity
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24- What is the function of radio receiver?
a) to detect and amplify information signal from the carrier
b) to modulate a message signal
c) to produce radio waves
d) to convert one form of energy into other
25- Sin wave is ________
a) Aperiodic Signal
b) Periodic Signal
c) Random Signal
d) Digital Signal
26- 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
27- Noise is added to a signal ________
a) In the channel
b) At receiving antenna
c) At transmitting antenna
d) During regeneration of information
28- Agreement between communication devices are called ________
a) Transmission medium
b) Channel
c) Protocol
d) Modem
29- Relationship between amplitude and frequency is represented by ________
a) Time-domain plot
b) Phase-domain plot
c) Frequency-domain plot
d) Amplitude-domain plot
Q.2 In front of each statement write either TRUE or FALSE
1. The speaker turns the voice into electrical signal
2. The human ear can listen to frequencies up to 150 kHz
3. The TV communication is a duplex communication system
4. Analog communication systems are more accurate than digital
ones
5. Your home telephone is connected to the switching via twisted
pair copper wire.
6. Radar systems are analog communication systems.
7. The receiver prepares the signal to be appropriate for
transmission
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8. At the transmitter, the antenna converts the electromagnetic
wave into a high frequency signal
9. The transmitting antenna converts the high frequency electrical
signal into electromagnetic wave.
10. The receiving antenna converts the electromagnetic wave into
high frequency electrical signal
11. Multiplexing is the simultaneous transmission of many signals
over the same channel
12. Filters
are
electrical/electronic
circuits
that
pass
some
frequencies and reject the others.
13. Coaxial cables have more bandwidth than twisted pairs.
14. Repeaters reduce the noise effects.
15. Channel capacity is a channel bandwidth.
16. A composite signal can be periodic or nonperiodic.
17. Baseband signal is not suitable for long distance communication.
18. The Modulated signal transmission is a Baseband transmission.
Q.3 Complete the following ……
1- The communication system in fig.:
..............
..............
..............
..............
..............
..............
..............
Q.4
1- The loss in a cable is usually defined in decibels per kilometer
(dB/km). If the signal at the beginning of a cable with − 0.3 dB/km
has a power of 2 mW, what is the power of the signal at 5 km?
2- The power of a signal is 10 mW and the power of the noise is 1µW;
what are the values of SNR and SNRdB?
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3- A nonperiodic composite signal has a bandwidth of 200 kHz, with a
middle frequency of 140 kHz and peak amplitude of 20 V. The two
extreme frequencies have amplitude of 0. Draw the frequency
domain (spectrum) of the signal.
4- If a periodic signal is decomposed into five sine waves with
frequencies of 100, 300, 500, 700, and 900 Hz, what is its
bandwidth? Draw the spectrum, assuming all components have a
maximum amplitude of 10 V.
5- Sketch the spectrum of the following ..
a) The unit impulse (t)
b) x(t) = 1
c) x(t) = cos(t)
d) x(t) = sin(t)
e) x(t) = rect(t/)
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END
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