BDS Customer Premises Equipment and Installation 1 — Questions and Answers
Question 1: What is the purpose of the ground block at a subscriber's home entry point?
- To amplify the signal entering the home
- To provide a weatherproof connector for outdoor cable
- To connect the coaxial shield to the home's grounding electrode system, protecting equipment from lightning and electrical surges (Correct answer)
- To split the signal to multiple rooms
Correct answer: To connect the coaxial shield to the home's grounding electrode system, protecting equipment from lightning and electrical surges
The ground block bonds the coaxial cable's outer shield to the home's grounding system, providing a path for lightning-induced surges to safely dissipate to earth rather than enter and damage subscriber equipment.
Question 2: What is a cable modem's downstream receive power operating range per DOCSIS specification?
- 0 to +10 dBmV
- –15 to +15 dBmV (Correct answer)
- –7 to +7 dBmV
- +10 to +30 dBmV
Correct answer: –15 to +15 dBmV
DOCSIS specifies that a cable modem must operate correctly with downstream SC-QAM signal levels between –15 dBmV and +15 dBmV, with an optimal range near 0 dBmV.
Question 3: What is a MoCA adapter and what problem does it solve?
- A modem-over-coax adapter that replaces the cable modem
- A device that uses existing coaxial cable in the home to create a home network, avoiding the need to run new Ethernet wiring (Correct answer)
- A coaxial cable amplifier for whole-home distribution
- A mesh Wi-Fi node that connects to the headend via coax
Correct answer: A device that uses existing coaxial cable in the home to create a home network, avoiding the need to run new Ethernet wiring
MoCA (Multimedia over Coax Alliance) adapters use the existing coaxial cable infrastructure in a home to carry gigabit Ethernet signals, enabling wired home networking without new cable installation.
Question 4: What does a cable technician check when a subscriber reports slow internet speeds but the modem appears online?
- Replace the modem immediately
- Check downstream receive power, upstream transmit power, SNR/MER, uncorrectables, and T3/T4 timeout counts in the modem's diagnostic page or CMTS (Correct answer)
- Verify the subscriber's credit card is on file
- Reboot the headend CMTS
Correct answer: Check downstream receive power, upstream transmit power, SNR/MER, uncorrectables, and T3/T4 timeout counts in the modem's diagnostic page or CMTS
Signal diagnostics — downstream power, upstream transmit power, SNR/MER, correctable/uncorrectable errors, and ranging event counts — reveal plant impairments that degrade throughput without taking the modem offline.
Question 5: What is the maximum recommended length for a standard RG-6 subscriber drop to maintain acceptable signal levels?
- 150 feet
- 300 feet (Correct answer)
- 500 feet
- 1,000 feet
Correct answer: 300 feet
RG-6 coax drops are generally limited to approximately 150–200 feet in residential installations; beyond 300 feet, signal loss becomes excessive and an amplifier or closer tap may be required.
Question 6: What is the function of a PoE (Point of Entry) filter installed at the ground block?
- It blocks all signals above 1 GHz from entering the home
- It prevents upstream ingress noise generated inside the home from entering the cable plant, while passing downstream signals unaffected (Correct answer)
- It amplifies the downstream signal to compensate for the ground block insertion loss
- It separates the MoCA home network signal from the DOCSIS upstream signal
Correct answer: It prevents upstream ingress noise generated inside the home from entering the cable plant, while passing downstream signals unaffected
A PoE filter (also called an ingress filter or home isolation filter) passes downstream signals but attenuates or blocks upstream frequencies, preventing household devices and wiring from injecting noise into the shared cable plant.
BDS Customer Premises Equipment and Installation 1
What is the purpose of the ground block at a subscriber's home entry point?