ECE121 – QUIZ 1 c. 290 K d.
580 K
MULTIPLE CHOICE – Choose the best answer. NO 8 How many international commercial AM 16 A kind of distortion due to sum and difference
ERASURE/S. Correct answer/s with alteration of any broadcast channels (assume BW = 10kHz) can of signals entering a non-linear device.
sort will not be given credit. (1 point each) fit into the bandwidth occupied by a a. harmonic
commercial FM broadcast channel (assume b. amplitude distortion
1 A complete communication system must BW = 200kHz)? c. intramodulation distortion
include a. 20 b. 200 c. 10 d. 5 d. intermodulation distortion
a. a transmitter and receiver
b. a transmitter, a receiver, and a channel 9 A naturally occurring disturbance that
c. a transmitter, a receiver, and a originates from the earth’s atmosphere
spectrum analyzer a. Solar Noise b. Cosmic 17 An increase in the equivalent resistance
d. a multiplexer, a demultiplexer, and a Noise generating the noise results to
channel c. Atmospheric Noise d. Man made a. an increase in the average noise power
Noise b. an increase in the rms noise voltage
2 If the measured wavelength is 6m, calculate c. a decrease in the average noise power
the frequency in MHz. 10 It is the relative strength of the desired signal d. a decrease in the average noise voltage
a. 25 MHz. b. 10 MHz. power to the noise power measured at the
c. 50 MHz d. 100 MHz. same point. 18 Which of the following is not used for
a. noise figure b. power communications?
3 A TV channel can accommodate ___ FM ratio a. X-rays b. Infrared
stations. c. signal-to-noise ratio d. noise c. Millimeter waves d. Microwaves
a. 6 b. 7 c. 8 d. 9 voltage
19 In a frequency domain plot, the horizontal
4 "Man-made" noise can come from 11 The equivalent noise temperature of an axis measures the ______.
a. equipment that sparks b. static amplifier is 25 ºK. What is the noise factor? a. Peak amplitude b. frequency
c. temperature d. all of the a. 0.913 b. 0.086 c. phase d. slope
above c. 1.086 d. 10.086
20 Simultaneous 2-way communications is
5 What percentage of the VHF band does a 6 12 The ideal noise figure is called________.
MHz TV signal occupy? a. 1 dB b. 0 dB a. Half-duplex b. Full-duplex
a. 2.2% b. 8.8% c. infinity d. none of the c. Bicomm d. Simplex
c. 4.4% d. 1.1% choices
IDENTIFICATION - . NO ERASURE/S. Correct
6 Signal-to-Noise ratio is calculated as 13 An amplifier has output S/N that is half of its answer/s with alteration of any sort will not be given
a. signal voltage divided by noise voltage input S/N. What is its noise figure? credit. (1 point each)
b. signal power divided by noise power a. 3 dB b. -3 dB
c. first add the signal power to the noise c. 2 dB d. none of the 1 Wavelength, in meters, of a 300 GHz
power, then divide by noise power choices electromagnetic wave.
d. none of the above 2 The totality of mechanisms that provide
14 Determine the noise current of a device for a information transfer.
7 Noise Figure is a measure of current of 5 mA and bandwidth of 3.2 kHz. 3 If you have an available number of amplifiers
a. how much noise is in a communications a. 1.6 µA b. 3.2 nA with a gain of 100 each, how many such
system c. 1.6 nA d. none of the amplifiers do you need to cascade to give an
b. how much noise is in the channel choices overall gain of 60dB?
c. how much noise an amplifier adds to a 4 Mode of transmission of cable television.
signal 15 What is the equivalent noise temperature for a 5 True or false. Full duplex is a type of
d. signal-to-noise ratio in dB noise figure of 3dB? transmission mode where a station can
a. 17 K b. 145 K transmit and receive signals at the same time
but not to and from the same station.
6 The standard FM Radio Broadcast is from 88
to 108 MHz. At which FCC frequency
designation is this band located?
7 This is a collection of electronic components
designed to convert the information into a
form suitable for transmission.
8 The frequency spectrum occupied by AM
broadcast system in the Philippines.
9 RF band of TV Channel 13.
10 Normal range of human speech.
11 Noise always affect the signal in a 2. For a non-ideal amplifier and the following
communication systems at the _____. parameters, Determine:
12 If the voltage change equal to twice the (a) Input S/N ratio in dB (2 points)
original value, what is the corresponding (b) Output S/N ratio in dB (2 points)
change in dB? (c) Noise factor and noise figure\ (3 points)
13 Random noise power is proportional to the Input Signal Power = 6.2 dBn
______ over which it is measured.
Input Noise Power = –62 dBn
14 In the FCC rules, the frequency band from 3 to
Power Gain = 75 dB
30 GHz is known as ______.
15 What is the shot noise current for a transistor Internal Noise (Nd) = 10.8 dBp
with a forward bias current of 1.25 mA
operating over a 70kHz bandwidth.
PROBLEMS
1. Four amplifiers with the following characteristics
are to be connected in cascade.
AMPLIFIER Power Gain Noise
Figure
A 10 dB 2 dB
B 6 dB 7 dB
C 8 dB 5 dB
D 14 dB 3 dB
A. What is the lowest overall noise factor
obtainable? (2 points)
B. Draw a diagram showing the connection of
the amplifiers that will give the lowest overall
noise factor. (2 points)
C. If the input signal power is 3 mW and the
input noise power is 5 nW, what is the output
signal power in dBm and the signal-to-noise
ratio at the output. Assume that the
amplifiers does not contribute noise
internally. (4 pts)
