System Technician
Which of the following statements about the amplitude modulation waveform is not true
- answer Only one frequency exists as it appears in the wave form
Regarding the modulation factor - answerit is the variation in the AM signal compared
with the unmodulated carrier
Which of the following is an advantage of standard AM signals - answerThe standard
AM System uses inexpensive transmitting and receiving equipment
With respect to high-level modulation - answerIn general a crystal oscillator is used for
stability if the transmitter is to be used at ta standard fixed frequency
The sensitivity of a receiver - answerIs determined by the amount of gain a receiver has
For superheterodyne receivers - answerThe principle of fixed tuning is used, mixing the
incoming RF signal with a signal generated within the receiver
The balanced modulator - answerType, called the balanced ring modulator, is capable
of suppressing the carrier by 60 dB, but the diodes must be carefully matched
The filter method of side-band suppression - answerMay use piezoelectric crystals to
produce the narrow pass bands and sharply defined skirts required to properly filter out
the unwanted side-band
The automatic gain control (AGC) - answerSystem can be achieved with conventional
diode rectifiers and additional amplification
Which of the following is not an advantage of single-side-band (SSB) communications
systems over standard AM systems - answerSSB offers more cost savings and system
simplicity than standard AM
What determines the frequency deviation and deviation rate of a frequency modulation -
answerThe frequency deviation is determined by the amplitude of the modulating signal
the deviation rate is determined by the frequency of the modulating signal
What must be known about the frequency modulation (FM) carrier before using a
Bessel function table to determine the number of significant side-bands which result
during modulation - answerThe maximum frequency deviation and the maximum
frequency of the modulation signal
,How does an audio signal modulate an RF carrier during direct frequency modulation -
answerAudio waves applied to a capacitor microphone, connected in parallel with the
tank circuit of an RF oscillator, vary the capacitance of the tank circuit in step with the
audio wave vibrations, causing the frequency of the RF wave generated by the oscillator
to vary in step with the audio wave
Why is automatic frequency control (AFC) required with a reactance modulator -
answerTo correct for any carrier frequency drift as a result of the instability of the
inductive/capacitive (LC) oscillator in the reactance modulator and to maintain
compliance with transmission standards for frequency accuracy.
What additional circuitry must be included with a phase modulator during frequency
modulation - answerAn integrator circuit must be included in a phase modulator to
detach the frequency deviation from the modulation signal frequency
What does the frequency multiplier do to the frequency and deviation of the frequency
modulation (FM) carrier - answerThe frequency multiplier is a class C amplifier with its
output circuitry tuned to a harmonic of the input frequency so that the frequency and
deviation of of the FM carrier are multiplied together
How is the output of a frequency modulation (FM) receiver maintained at a relatively
constant level despite fluctuations of the input signal level - answerAutomatic Gain
Control (AGC) is employed to adjust the gain of the receivers RF amplifier stage so that
the amplitude of the limiters input signal is fairly constant
How does the discriminator demodulate the frequency modulation (FM) carrier -
answerThe FM discriminator converts the frequency variations of the FM carrier into
voltages where the amplitude voltage is proportional to the carrier frequency deviation
and the voltage frequency is proportional to the carrier frequency deviation rate.
List the critical elements of a good phase-locked loop (PLL) discriminator circuit -
answerFirst the phase detector must produce a linear output over the range of input
signals from the limiter and voltage controlled oscillator (VCO) Second, the low-pass
filter determines the bandwidth and throughput of the PLL. Third, the VCO must be
linear and produce a constant change in frequency per volt of control signal
Why must a limiter stage precede the Foster-Seeley phase discriminator -
answerBecause the Foster-Seeley phase discriminator circuit is also sensitive to
amplitude variations in the frequency modulation (FM) wave
According to SCTE-and NCTA- recommended trunk system map symbols, fiber-optic
cable is represented - answerDouble arrows within a small circle on a solid line
, The forward path signal in a traditional tree-and branch architecture - answerOriginates
at the head end and is transmitted downstream through coaxial trunk cable and trunk
amplifier
In an HFC network - answerProcessing equipment in the head end converts the forward
RF signal to a light signal
During aerial plant construction - answerThe strand is tensioned so its sag profile
matches that of the overhead utility power lines.
With underground plan construction - answerThe fiber-optic and coaxial cables are
often placed underground with other utility lines to jointly share construction cost.
Standby power supplies - answerContinue providing an output voltage even during a
utility power outage by using a backup power source.
Centralized power configurations - answerProvide the advantage of increased reliability
through sharing of expensive backup generators and sophisticated monitoring
equipment among different power realms.
When transmitting broadband signals - answerIna two-way HFC network, two or more
individual optical fibers are required for each optical node location.
RF trunk amplifiers - answerHave attenuator pads, equalizers, and diplex filters that
control and route the RF signals.
Verifying plant reliability includes - answerFrequency response sweeping, which is
adjusting RF amplifier circuits to amplify all frequencies in the bandpass spectrum as
equally as possible.
which of the following statements about aural communications and its history is NOT
true? - answerWireless telegraphic transmission became practical many years before
the vacuum tube was perfected.
Concerning the history of visual communications, - answerArpanet's descendants form
the global backbone of the internet
Which statement about modulation is accurate? - answerModulation may be high-level
or low-level, depending on the point in the system at which the modulating signal is
injected.
Which of the following is NOT a type of modulation used by communications systems? -
answerShield modulation
Which of the following statements about the amplitude modulation waveform is not true
- answer Only one frequency exists as it appears in the wave form
Regarding the modulation factor - answerit is the variation in the AM signal compared
with the unmodulated carrier
Which of the following is an advantage of standard AM signals - answerThe standard
AM System uses inexpensive transmitting and receiving equipment
With respect to high-level modulation - answerIn general a crystal oscillator is used for
stability if the transmitter is to be used at ta standard fixed frequency
The sensitivity of a receiver - answerIs determined by the amount of gain a receiver has
For superheterodyne receivers - answerThe principle of fixed tuning is used, mixing the
incoming RF signal with a signal generated within the receiver
The balanced modulator - answerType, called the balanced ring modulator, is capable
of suppressing the carrier by 60 dB, but the diodes must be carefully matched
The filter method of side-band suppression - answerMay use piezoelectric crystals to
produce the narrow pass bands and sharply defined skirts required to properly filter out
the unwanted side-band
The automatic gain control (AGC) - answerSystem can be achieved with conventional
diode rectifiers and additional amplification
Which of the following is not an advantage of single-side-band (SSB) communications
systems over standard AM systems - answerSSB offers more cost savings and system
simplicity than standard AM
What determines the frequency deviation and deviation rate of a frequency modulation -
answerThe frequency deviation is determined by the amplitude of the modulating signal
the deviation rate is determined by the frequency of the modulating signal
What must be known about the frequency modulation (FM) carrier before using a
Bessel function table to determine the number of significant side-bands which result
during modulation - answerThe maximum frequency deviation and the maximum
frequency of the modulation signal
,How does an audio signal modulate an RF carrier during direct frequency modulation -
answerAudio waves applied to a capacitor microphone, connected in parallel with the
tank circuit of an RF oscillator, vary the capacitance of the tank circuit in step with the
audio wave vibrations, causing the frequency of the RF wave generated by the oscillator
to vary in step with the audio wave
Why is automatic frequency control (AFC) required with a reactance modulator -
answerTo correct for any carrier frequency drift as a result of the instability of the
inductive/capacitive (LC) oscillator in the reactance modulator and to maintain
compliance with transmission standards for frequency accuracy.
What additional circuitry must be included with a phase modulator during frequency
modulation - answerAn integrator circuit must be included in a phase modulator to
detach the frequency deviation from the modulation signal frequency
What does the frequency multiplier do to the frequency and deviation of the frequency
modulation (FM) carrier - answerThe frequency multiplier is a class C amplifier with its
output circuitry tuned to a harmonic of the input frequency so that the frequency and
deviation of of the FM carrier are multiplied together
How is the output of a frequency modulation (FM) receiver maintained at a relatively
constant level despite fluctuations of the input signal level - answerAutomatic Gain
Control (AGC) is employed to adjust the gain of the receivers RF amplifier stage so that
the amplitude of the limiters input signal is fairly constant
How does the discriminator demodulate the frequency modulation (FM) carrier -
answerThe FM discriminator converts the frequency variations of the FM carrier into
voltages where the amplitude voltage is proportional to the carrier frequency deviation
and the voltage frequency is proportional to the carrier frequency deviation rate.
List the critical elements of a good phase-locked loop (PLL) discriminator circuit -
answerFirst the phase detector must produce a linear output over the range of input
signals from the limiter and voltage controlled oscillator (VCO) Second, the low-pass
filter determines the bandwidth and throughput of the PLL. Third, the VCO must be
linear and produce a constant change in frequency per volt of control signal
Why must a limiter stage precede the Foster-Seeley phase discriminator -
answerBecause the Foster-Seeley phase discriminator circuit is also sensitive to
amplitude variations in the frequency modulation (FM) wave
According to SCTE-and NCTA- recommended trunk system map symbols, fiber-optic
cable is represented - answerDouble arrows within a small circle on a solid line
, The forward path signal in a traditional tree-and branch architecture - answerOriginates
at the head end and is transmitted downstream through coaxial trunk cable and trunk
amplifier
In an HFC network - answerProcessing equipment in the head end converts the forward
RF signal to a light signal
During aerial plant construction - answerThe strand is tensioned so its sag profile
matches that of the overhead utility power lines.
With underground plan construction - answerThe fiber-optic and coaxial cables are
often placed underground with other utility lines to jointly share construction cost.
Standby power supplies - answerContinue providing an output voltage even during a
utility power outage by using a backup power source.
Centralized power configurations - answerProvide the advantage of increased reliability
through sharing of expensive backup generators and sophisticated monitoring
equipment among different power realms.
When transmitting broadband signals - answerIna two-way HFC network, two or more
individual optical fibers are required for each optical node location.
RF trunk amplifiers - answerHave attenuator pads, equalizers, and diplex filters that
control and route the RF signals.
Verifying plant reliability includes - answerFrequency response sweeping, which is
adjusting RF amplifier circuits to amplify all frequencies in the bandpass spectrum as
equally as possible.
which of the following statements about aural communications and its history is NOT
true? - answerWireless telegraphic transmission became practical many years before
the vacuum tube was perfected.
Concerning the history of visual communications, - answerArpanet's descendants form
the global backbone of the internet
Which statement about modulation is accurate? - answerModulation may be high-level
or low-level, depending on the point in the system at which the modulating signal is
injected.
Which of the following is NOT a type of modulation used by communications systems? -
answerShield modulation
