PROGRESSION: MAINTENANCE TECH
I - II CONVENTIONAL QUESTIONS AND
CORRECT ANSWERS
Why is it imperative to keep all ingress and impulse noise, even that outside the frequency range of
the RF return carriers, to a minimum? ANSW✅✅Regardless of the frequency, if the impulse noise
or ingress is high enough, it can cause laser clipping.
When looking at a cable modem's PreEqualization Tap response, what do you know if the ninth bar
is less than 10 dB below the eighth bar? ANSW✅✅That there are high micro-reflections and that
the cause is near the modem, likely in the drop system.
What practice can uncover potential return path problems in the drop system that can be mitigated
before entering the network? ANSW✅✅Prescreening the drop system for ingress or egress.
Why is installing high-pass filters (HPF) at the tap on drops without two-way services considered a
short-term solution to ingress and impulse noise migrating into the hybrid fiber/coax (HFC) network?
ANSW✅✅The HPF will have to be removed when cable modems and digital set-top boxes (STB)
are activated at the addresses that have an HPF installed.
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What should be done before diagnosing a return path problem in the drop system?
ANSW✅✅Confirm that the hybrid fiber/coax (HFC) network is working properly.
What spectrum analyzer function is particularly useful as it captures and holds ingress, impulse
noise, and other impairments on its display so that they can be viewed and analyzed?
ANSW✅✅The Max Hold function.
What should be done when the location of electrical interference in the power network is identified?
ANSW✅✅Notify the power company with the exact location so the cause of the interference can
be repaired.
What can be used with a signal level meter (SLM) to check the drop system for RF continuity at sub-
band frequencies? ANSW✅✅A signal generator.
, What information can be gathered by a return path monitoring system that captures the quadrature
amplitude modulation (QAM) return channel from a DOCSIS modem? ANSW✅✅The group delay,
in-band ripple/tilt, and micro-reflections on the QAM channel.
What feature of DOCSIS proactive network maintenance (PNM) can save the technician hours of
troubleshooting? ANSW✅✅PNM performs correlation of data from all the modems in an area to
pinpoint where the likely problem in the network can be found.
When should a preamplifier be used to measure impairments with a spectrum analyzer?
ANSW✅✅If the noise floor drops less than 10 dB when the input signal is removed from the
spectrum analyzer.
What does the spectrum analyzer Zero Span function do? ANSW✅✅The Zero Span function stops
the analyzer's sweep and parks its tuner to a specific frequency, displaying amplitude vs. time
How is laser clipping in the return path characterized on a spectrum analyzer? ANSW✅✅By an
elevated noise floor above 42 MHz after the optical signal has been converted back to RF, typically in
the headend.
If a return path impairment appears to be caused by impulse noise, why is it a good idea to begin
troubleshooting at distribution taps of 17 dB or lower? ANSW✅✅Low value taps have less
isolation between ports and offer less attenuation to ingress and impulse noise coming from an
individual drop system.
What amplitude level should the output of return amplifiers be adjusted? ANSW✅✅So that the
amplifier gain is equal to the path attenuation that follows the amplifier.
What should be checked if a large percentage of set-top boxes (STB) transmit above 55 dBmV, the
upper end of the STB transmission level range? ANSW✅✅The value of the attenuator pad at the
input of the STB demodulator.
What type of measurement removes any errors attributable to bandwidth and provides an "apples-
to-apples" comparison between carriers of differing bandwidths? ANSW✅✅The constant power
per hertz (power/Hz) measurement.
I - II CONVENTIONAL QUESTIONS AND
CORRECT ANSWERS
Why is it imperative to keep all ingress and impulse noise, even that outside the frequency range of
the RF return carriers, to a minimum? ANSW✅✅Regardless of the frequency, if the impulse noise
or ingress is high enough, it can cause laser clipping.
When looking at a cable modem's PreEqualization Tap response, what do you know if the ninth bar
is less than 10 dB below the eighth bar? ANSW✅✅That there are high micro-reflections and that
the cause is near the modem, likely in the drop system.
What practice can uncover potential return path problems in the drop system that can be mitigated
before entering the network? ANSW✅✅Prescreening the drop system for ingress or egress.
Why is installing high-pass filters (HPF) at the tap on drops without two-way services considered a
short-term solution to ingress and impulse noise migrating into the hybrid fiber/coax (HFC) network?
ANSW✅✅The HPF will have to be removed when cable modems and digital set-top boxes (STB)
are activated at the addresses that have an HPF installed.
Main Menu2of12
What should be done before diagnosing a return path problem in the drop system?
ANSW✅✅Confirm that the hybrid fiber/coax (HFC) network is working properly.
What spectrum analyzer function is particularly useful as it captures and holds ingress, impulse
noise, and other impairments on its display so that they can be viewed and analyzed?
ANSW✅✅The Max Hold function.
What should be done when the location of electrical interference in the power network is identified?
ANSW✅✅Notify the power company with the exact location so the cause of the interference can
be repaired.
What can be used with a signal level meter (SLM) to check the drop system for RF continuity at sub-
band frequencies? ANSW✅✅A signal generator.
, What information can be gathered by a return path monitoring system that captures the quadrature
amplitude modulation (QAM) return channel from a DOCSIS modem? ANSW✅✅The group delay,
in-band ripple/tilt, and micro-reflections on the QAM channel.
What feature of DOCSIS proactive network maintenance (PNM) can save the technician hours of
troubleshooting? ANSW✅✅PNM performs correlation of data from all the modems in an area to
pinpoint where the likely problem in the network can be found.
When should a preamplifier be used to measure impairments with a spectrum analyzer?
ANSW✅✅If the noise floor drops less than 10 dB when the input signal is removed from the
spectrum analyzer.
What does the spectrum analyzer Zero Span function do? ANSW✅✅The Zero Span function stops
the analyzer's sweep and parks its tuner to a specific frequency, displaying amplitude vs. time
How is laser clipping in the return path characterized on a spectrum analyzer? ANSW✅✅By an
elevated noise floor above 42 MHz after the optical signal has been converted back to RF, typically in
the headend.
If a return path impairment appears to be caused by impulse noise, why is it a good idea to begin
troubleshooting at distribution taps of 17 dB or lower? ANSW✅✅Low value taps have less
isolation between ports and offer less attenuation to ingress and impulse noise coming from an
individual drop system.
What amplitude level should the output of return amplifiers be adjusted? ANSW✅✅So that the
amplifier gain is equal to the path attenuation that follows the amplifier.
What should be checked if a large percentage of set-top boxes (STB) transmit above 55 dBmV, the
upper end of the STB transmission level range? ANSW✅✅The value of the attenuator pad at the
input of the STB demodulator.
What type of measurement removes any errors attributable to bandwidth and provides an "apples-
to-apples" comparison between carriers of differing bandwidths? ANSW✅✅The constant power
per hertz (power/Hz) measurement.
