EST Essentials - Chapter 1 Concepts
"Man-made" noise came from a. equipment that sparks b. temperature c. static d. all of the above
a
A more precise evaluation of the quality of a receiver as far as noise is concerned a. S/N b. VSWR c. noise factor d. noise margin
a
As frequency increase, the period: a. decreases b. increases c. remains the same d. doubles
a
Electrical energy at a frequency of 7125kHz is in what frequency range? a. radio b. audio c. hyper d. super-high
a
Electromagnetic waves produced primarily by heat are called: a. infrared rays b. microwaves c. shortwaves d. x-rays
a
If a periodic waveform is symmetric about the vertical axis, it is said to have axes, or mirror, symmetry and is called a/n a. even function b. odd function c. half-wave symmetry d. full-wave symmetry
a
If bandwidth is tripled, the signal power is;: a. not changed b. quadrupled c. tripled d. doubled
a
In a frequency-domain plot, the vertical axis measures the: a. peak amplitude b. frequency c. phase d. slope
a
In a time-domain plot, the vertical axis is a measure of: a. amplitude b. frequency c. phase d. time
a
Indicate the false statement. Fourier analysis shows that a sawtooth wave consist of: a. fundamental and subharmonic sine waves b. a fundamental sine wave and an infinite number of harmonics c. fundamental and harmonic sine waves whose amplitude decreases with the harmonic number d. sinusoidal voltages, some of which are small enough to ignore in practice
a
Indicate the false statement. Modulation is used to: a. reduce the bandwidth used b. separate differing transmissions c. ensure that intelligence may be transmitted over long distances d. allow the use of practicable antennas
a
Noise at the input to a receiver can be as high as several: a. microvolts b. millivolts c. volts d. kilovolts
a
Noise is primarily: a. high-frequency spikes b. low-frequency variations c. random level shifts d. random frequency variations
a
Radians per second is equal to a. 2pi + f b. f / 2pi c. the phase angle d. none of the above
a
Shot noise is generated in a. transistors and diodes b. resistors c. copper wire d. none of the above
a
Solar noise: a. a constant radiation from the sun b. RF noise radiated by distant stars c. a constant radiation from the sun and RF noise radiated by distant stars d. none of the above
a
The Hartley oscillator uses: a. a tapped inductor b. a two-capacitor divider c. an RC time constant d. a piezoelectric crystal
a
What class of operation has the highest fidelity? a. A b. C c. AB d. AC
a
What electrical characteristic makes the frequency stability of a crystal better than that of an LC tank circuit? a. higher Q b. higher inductance c. higher resistance d. higher capacitance
a
What is attenuation? a. the signal loses strength due to the resistance of the transmission medium b. the signal loses strength due to the different propagation speeds of each frequency that makes up the signal c. an outside source such as crosstalk corrupts a signal d. any of these
a
Which noise figure represents the lowest noise? a. 1.5dB b. 2.0dB c. 3.7dB d. 4.1dB
a
Which of the following can be determined from a frequency-domain graph of a signal? a. bandwidth b. phase c. power d. all of the above
a
Which of the following describes white noise? a. noise that is produced by random motion of electrons in a conductor due to heat b. noise that is die to random variations in current flow in active devices such as tubes, transistors, semiconductor diodes, etc c. noise power that varies inversely with frequency d. any modification to a stream of carriers as they pass from input to output of a device produces an irregular, random variation
a
Which of the following is not a source of external noise? a. thermal agitation b. auto ignitions c. the sun d. fluorescent lights
a
Which of the following is not a source of noise? a. another communication signal b. atmospheric effects c. manufactured electrical systems d. thermal agitation in electronics components
a
Which of the following is not a source of noise? a. another communications signal b. atmospheric effects c. manufactured electrical systems d. thermal agitation in electronic components
a
Which of the following is not an actual amount of power? a. dB b. dBm c. dBw d. dBk
a
Which of the following is not used for communications? a. x-rays b. millimeter waves c. infrared d. microwaves
a
Which of the following oscillators is used to provide a highly stable output stable output at a very precise frequency? a. crystal b. hartley c. colpitts d. armstrong
a
Why are amplifiers used in electronic devices? a. to provide signals of usable amplitude b. to "pick up" broadcast signal c. to select the proper broadcast signal d. to change the broadcast signal to an audio signal
a
_______ is mathematically equal to the logarithm to the base ten of the power ratio P1 over P2. a. bel b. dB c. bel/10 d. dB/2
a
"Pink" noise has a. equal power per Hertz b. equal power per octave c. constant power d. none of the above
b
A class B amplifier conducts for how many degrees of an input sine wave? a. 90 deg to 150 deg b. 180 deg c. 180 deg to 360 deg d. 360 deg
b
A complete communication system must include: a. a transmitter and receiver b. a transmitter, a receiver, and a channel c. a transmitter, a receiver, and a spectrum analyzer d. a multiplexer, a demultiplexer, and a channel
b
A micron is a. one-millionth of a foot b. one-millionth of a meter c. one-thousandth of a meter d. one ten-thousandth of an inch
b
A periodic signal can always be decomposed into: a. exactly an odd number b. a set of sine waves c. a set of sine waves, one of which must have a phase set of 0 degrees d. none of the above
b
A signal is measured at two different points. The power is P1 at the first point and P2 at the second point. The dB is 0. This means: a. P2 is zero b. P2 equals P1 c. P2 is much larger than P1 d. P2 is much smaller than P1
b
An analog signal is a. continuous signal which represents digital measurements b. continuous signal which represents physical measurements c. discrete time signals generated by analog modulation d. discrete time signals generated by digital modulation
b
Approximate wavelength of green light: a. 700nm b. 530nm c. 475nm d. 400nm
b
Continuous voice or video signals are referred to as being a. baseband b. analog c. digital d. continuous waves
b
Cosmic nose: a. a constant radiation from the sun b. RF noise radiated by distant stars c. a constant radiation from the sun and RF noise radiated by distant stars d. none of these
b
If a periodic voltage waveform is symmetric about a line midway between the vertical axis and the negative horizontal axis and passing through the coordinate origin, it is said to have point, or skew, symmetry is call a/n: a. even function b. odd function c. half-wave symmetry d. full-wave symmetry
b
If the output of a circuit should be a representation of less than one-half of the input signal, what class of operation should be used? A. A B. C C. AB D. AC
b
In half duplex communications a. there is only one way of transmission b. only one of the two parties can transmit at a time c. both parties may transmit and receive simultaneously d. there is no half duplex communication
b
Indicate the false statement. From the transmitter the signal deterioration because of noise is usually: a. unwanted energy b. predictable in character c. present in the transmitter d. due to any cause
b
Noise can be reduced by: a. widening the bandwidth b. narrowing the bandwidth c. increasing temperature d. increasing transistor current levels
b
Propagation time is _____ proportional to distance and ______ proportional to propagation speed a. inversely, directly b. directly, inversely c. inversely, inversely d. directly, directly
b
Radio signals are made up of a. voltages and currents b. electric and magnetic fields c. electrons and protons d. noise and data
b
So called "1/f" noise is also called a. random noise b. pink noise c. white noise d. partition noise
b
The Clapp oscillator is: a. a modified Hartley oscillator b. a modified Colpitts oscillator c. a type of crystal-controlled oscillator d. only built with FETs
b
The Colpitts VFO uses: a. a tapped inductor b. a two-capacitor divider c. an RC time constant d. a piezoelectric crystal
b
The baseband signal cannot usually be transmitted through space by radio because: a. the antennas required are too short b. multiple base band signals transmitting simultaneously would interfere with one another c. the signal will be attenuated d. any of these
b
The degree to which a cycle has been completed at any given instant is referred to as the: a. phase b. period c. frequency d. amplitude
b
The following are characteristics of atmospheric noise, except: a. it is caused by lightning discharges in thunderstorms b. dominates at higher frequencies c. has a very high peak-to-average power ratio d. also called static noise
b
The following are the characteristics of industrial noise except: a. noise that is due to automobile and aircraft ignition, electric motors and switching equipment, leakage from high voltage lines, fluorescent lamps, etc. b. usually between 1-600 GHz c. usually most intense in industrial and densely populated areas d. also called man-made noise
b
The part of sinewave that is above the voltage reference line is referred to as the: a. peak amplitude b. positive alternation c. negative alternation d. instantaneous amplitude
b
The term "bel" is a unit of measurement that expresses which of the following relationships a. ratio of voltage and resistance b. logarithmic ratio between input and output c. geometric progression from input to output d. ratio of voltage to current
b
The unit "decibel" is used to indicate a. an oscilloscope wave form b. a mathematical ratio c. a certain radio waves d. a single side band signal
b
What is an oscilloscope? a. a description of signal with respect to time b. an instrument that shows signal waveforms c. a description of signal with respect to its frequency d. an instrument that shows amplitude-versus-frequency plot
b
What is correlated noise? a. noise that is present regardless of whether there is signal present or not b. noise that cannot be present in the circuit unless there is an input signal c. noise that affects the communication system coming from the outside environment d. noise which is generated internally or within the communication system or in the receiver
b
What is distortion? a. the signal loses strength due to the resistance of the transmission medium b. the signal loses strength due to the different propagation speeds of each frequency that makes up the signal c. an outside source such as crosstalk corrupts a signal d. any of these
b
What is true about noise limiter? a. suppressed low frequency noise components b. prevents externally generated noise from exceeding certain amplitude c. it is inserted in series wit the a-c power cord of an electronic device d. any of these
b
What three circuits are most commonly used as frequency determining devices? a. class C amplifier, class B amplifier, and class A amplifier b. crystal-controlled oscillator, RC oscillator, and LC oscillator c. common-emitter amplifier, common-base amplifier, and common-collector amplifier d. transformer coupler, RC coupler, and direct coupler
b
Which of the following describes shot noise? a. noise that is produced by random motion of electrons in a conductor due to heat b. noise that is due to random variations in current flow in active devices such as tubes, transistors, semiconductor diodes, etc. c. noise power that varies inversely with frequency d. any modification to a stream of carrier as they pass from input to output of a device produces an irregular, random variation
b
Which of the following is different from the other? a. facsimile b. telemetry c. videotex d. teletex
b
An ideal sinusoidal oscillator would produce which of the following outputs? a. a square wave of constant frequency and amplitude b. a square wave of varying frequency and amplitude c. a sine wave of constant frequency and amplitude d. a sine wave of varying frequency and constant amplitude
c
Another name for signals in the HF range is a. microwaves b. RF waves c. shortwaves d. millimeter waves
c
If a periodic voltage waveform is such that the waveform for the first half cycle repeats itself expect with the opposite sign for the second half cycle, it is said to have a. even function b. odd function c. half-wave symmetry d. full-wave symmetry
c
If the maximum amplitude of a sine wave is 2V, the minimum amplitude is ____V. a. 2 b. 1 c. -2 d. between -2 and 2
c
Indicate the false statement. The need for modulation can best be exemplified by the following a. antenna lengths will be approximately λ/4 long b. an antenna in the standard broadcast am band is 16,000 ft c. all sound is concentrated from 20Hz to 20kHz d. a message is composed of unpredictable variations in both amplitude and frequency
c
Indicate the false statement. The square of the thermal noise voltage generated by a resistor is proportional to a. its resistance b. its temperature c. Boltzmann's constant d. the bandwidth over which it is measured
c
Most internal noise come from a. shot noise b. transit-time noise c. thermal agitation d. skin effect
c
Noise figure is a measure of a. how much noise is in a communications system b. how much noise is in the channel c. how much noise an amplifier add to a signal d. signal-to-noise ratio in dB
c
Radiowave spectrum is from ____ to _____. a. ELF, EHF b. VF, EHF c. VLF, EHF d. VLF, Light Frequencies
c
Television broadcasting occurs in which ranges? a. HF b. EHF c. VHF d. UHF
c
The communications medium causes the signal to be a. amplified b. modulated c. attenuated d. interfered with
c
The original electrical information signal to be transmitted is called the a. modulating signal b. carrier c. baseband signal d. source signal
c
The power density of "flicker" noise is a. the same at all frequencies b. greater at high frequencies c. greater at low frequencies d. the same as "white noise"
c
The three primary communications media are the following, except: a. wires b. free space c. waveguides d. fiber optic cable
c
The wavelength of a radio signal is a. equal to f/c b. equal to c/lambda c. the distance a wave travels in one period d. how far the signal can travel without distortion
c
What happens to a signal's frequency as its wavelength gets longer? a. it disappears b. it stays the same c. it goes down d. it goes up
c
What is noise? a. the signal loses strength due to the resistance of the transmission medium b. the signal loses strength due to different propagation speeds of each frequency that makes up the signal c. an outside source such as crosstalk corrupts a signal d. any of thes
c
What is simplex operation? a. transmitting and receiving over a wide area b. transmitting on one frequency and receiving on another c. transmitting one-way communications d. transmitting and receiving on the same frequency
c
Which of the following advantages does the Colpitts oscillator have over the Armstrong and Hartley oscillators? a. easier to tune b. wider frequency range c. better frequency stability d. all of the above
c
Which of the following describes pink noise? a. noise that is produced by random motion of electrons in a conductor due to heat b. noise that is due to random variations in current flow in active devices such as tubes, transistors, semiconductor diodes, etc c. noise power that varies inversely with frequency d. any modification to a stream of a device produces an irregular, random variation
c
Which of the following describes transistor noise? a. noise that is produced by random motion of electrons in a conductor due to heat b. noise that is due to random variations in current flow in active devices such as tubes, transistors, semiconductor diodes, etc. c. noise that occurs only in devices where signal current separates into two or more paths d. any modification to a stream of carriers as they pass from input to output of a device produces an irregular, random variation
c
A digital signal is a a. continuous signal which represents digital measurements b. continuous signal which represents physical measurements c. discrete time signal generated by analog modulation d. discrete time signal generated by digital modulation
d
A display of signal amplitude versus frequency is called the a. time domain b. frequency spectrum c. amplitude spectrum d. frequency domain
d
A signal is composed of a fundamental frequency of 2kHz and another of 4kHz. This 4kHz signal is referred to as: a. a fundamental of the 2kHz signal b. the DC component of the main signal c. a dielectric signal of the main signal d. a harmonic of the 2kHz signal
d
Crystal-controlled oscillators are a. used for a precise frequency b. used for very low frequency drift (parts per million) c. made for grinding quartz to extract dimensions d. all of the above
d
Distortion is caused by: a. creation of harmonics of baseband frequencies b. baseband frequencies "mixing" with each other c. shift in phase relationships between baseband frequencies d. all of the above
d
For a given bandwidth signal, more channel space is available for signals in the range of a. HF b. UHF c. SHF d. EHF
d
Noise in communication systems originates in: a. the sender b. the receiver c. the channel d. all of the above
d
Random interference to transmitted signals is called a. adjacent channel overlap b. cross talk c. garbage-in-garbage-out d. noise
d
Signal attenuation can be corrected by: a. filtering b. modulation c. equalization d. amplification
d
The most efficient RF power amplifier is which class amplifier? a. Class B b. Class A. c. Class AB d. Class C
d
The value of a resistor creating thermal noise is tripled. The noise power generated is therefore: a. halved b. quadrupled c. doubled d. unchanged
d
The wavelength of a signal depends on the a. frequencies of the signal b. medium c. phase of the signal d. a and b
d
Thermal noise is generated in a. transistors and diodes b. resistors c. copper wire d. all of the above
d
Wavelength is ________ proportional to propagation speed and ________ proportional to period. a. inversely; directly b. directly; inversely c. inversely; inversely d. directly; directly
d
What happens to a signal's wavelength as its frequency increases? a. it gets longer b. it stays the same c. it disappears d. it gets shorter
d
What is spectrum analyzer? a. a description of signal with respect to time b. an instrument that shows signal waveforms c. a description of signal with respect to its frequencies d. all of the above
d
Which of the following characterizes impulse noise? a. it is characterized by low-amplitude peaks of long duration in the total noise spectrum b. produced when unwanted harmonics of a signal are produced through non-linear amplification c. it is the generation of unwanted sum and difference frequencies when two or more signals are amplified by a non-linear device d. consists of sudden burst of irregularly shaped pulses
d
Which of the following describes transit time noise? a. noise that is produced by random motion of electrons in a conductor due to heat b. noise that is due to random variations in current flow in active devices such as tubes, transistors, semiconductor diodes, etc. c. noise power that varies inversely with frequency d. any modification to a stream of carriers as they pass from input to output of a device produces an irregular, random variation
d
Which of the following statements describes the relationship of input and output signals in an amplifier? a. the input signal is actually changed into the output signal b. both the input and output signal are unchanged; neither is affected by the other c. all sound is concentrated from 20Hz to 20kHz d. a message is composed of unpredictable variations in both amplitude and frequency
d
Why do we call signals in the range 20kHz to 20 000 Hz audio frequencies? a. because the human ear cannot sense anything in this range b. because this range is too low for radio energy c. because the human ear can sense radio waves in this range d. because the human ear can sense sound in this range
d