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Cable 101- Passive Troubleshooting

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1. Which category of network components includes splitters, taps, and coaxial cable?
Active Components Power Components Digital Components Passive Components
2. The total signal loss in a drop line is a combination of the cable attenuation and the loss from all which type of devices?
Active amplifiers Power supplies Video processors Passive devices (splitters, couplers, etc.)
3. If a technician measures a high Return Loss (low numerical value) at a customer's modem, what is the most likely cause?
Excessive amplifier gain in the trunk line Ingress noise entering the upstream path A poorly made connection or faulty connector creating an impedance mismatch The modem is overheating and failing
4. What is the industry-standard impedance in Ohms that all CATV coaxial cable and passive devices must maintain for optimal signal transmission?
100 300 75 50
5. Which tool is used to locate a fault or break in a coaxial cable by sending a pulse down the line and measuring the time it takes for the reflection to return?
Digital Multi-meter (DMM) Spectrum Analyzer Time Domain Reflectometer (TDR) Return Path Ingress Monitor (RPIM)
6. If a cable modem intermittently loses connectivity and diagnostics show high Corrected codeword errors but low Uncorrected codeword errors, the issue is most likely a:
Total loss of signal -40dBmV Severe impedance mismatch causing extreme reflections Minor signal impairment, such as low-level noise or marginal signal level Headend equipment failure
7. What is the primary technical consequence of using a non-approved, cheap, or damaged 'barrel splice' (coupler) to extend a coaxial cable?
It will reverse the signal polarity, causing video to display upside down. It will automatically amplify the signal, causing over-modulation. It will introduce significant insertion loss and create a serious impedance mismatch leading to reflections. It will filter out all the upstream (return) path frequencies.
8. During a routine drop installation, a technician should ALWAYS attach the ground block to which safety feature of the home's electrical system?
A nearby water spigot or garden hose connection The main power line neutral wire (white wire) inside the service panel The commercial power meter post, or a dedicated copper rod driven into the earth near the main service entrance The cable's center conductor to complete the DC circuit
9. What common troubleshooting symptom is often associated with Ingress (external RF noise entering the cable), particularly in the low-frequency Upstream path?
The downstream TV channels are completely black and silent. The cable modem struggles to maintain a connection, showing a high level of uncorrected errors. Only the highest-frequency channels are lost, while low-frequency channels are clear. The TV displays a message about HDCP copy protection failure.
10. A splitter is marked with a loss value of -3.5dB per leg. What does this loss value primarily represent?
The amount of noise the splitter will introduce to the signal. The maximum frequency the splitter can pass before failing. The intentional reduction in signal power due to dividing the signal path. The amount of AC power consumed by the splitter.
11. If a technician attempts to terminate a coaxial cable and finds strands of the shield braid touching the center conductor, this fault will cause a:
Dead short, resulting in high return loss and zero signal. Perfect impedance match, maximizing signal transfer. Loss of only the upstream path, while the downstream path remains operational. A DC voltage surge that damages the television.
12. Which signal measurement, specifically in digital services, is the best indicator of a low-level noise floor or subtle distortion that can cause intermittent errors?
DC voltage level Signal Level (dBmV) Modulation Error Ratio (MER) or Signal-to-Noise Ratio (SNR) Return Loss (RL)
13. If a technician observes a 'tilted' signal spectrum, where high-frequency channels have significantly lower power than low-frequency channels, the likely cause is:
The use of an active amplifier at the customer's premises. A short-circuit in the coaxial cable. The normal property of coaxial cable attenuation over distance, where high frequencies are lost more rapidly. The deliberate filtering of high-frequency data channels by the headend.
14. What is the recommended method for sealing outdoor coaxial cable connections (such as on taps or splitters) against moisture and corrosion?
Wrapping the connection tightly with black electrical tape. Applying silicone caulk directly over the connection points. Using dielectric grease on the threads followed by a weather-resistant compression seal or weather boot. Leaving the connection unsealed, as modern connectors are fully weatherproof.
15. What does a measurement of Egress indicate in a CATV network?
External noise entering the cable system from the outside. The signal power loss caused by a passive splitter. RF signal leakage from the cable system into the atmosphere. The quality of the video after passing through the set-top box.
16. When troubleshooting a tap, which statement is true regarding the signal level on the 'out' port (signal continuation) versus the 'tap' port (subscriber connection)?
The signal level on the 'out' port must be 10dBmV higher than the 'tap' port. The signal level on the 'tap' port must be significantly lower than the 'out' port to allow the signal to continue down the line. The signal level on both the 'out' and 'tap' ports must be exactly the same. Only the quality (MER) of the 'tap' port needs to be checked.
17. What is the maximum cable length for a standard RG-6 drop before attenuation becomes a critical issue for high-frequency services (like DOCSIS 3.1)?
There is no limit, as long as the signal is amplified at the demarcation point. Around 500 feet (152 meters). Around 150 feet (46 meters). Less than 20 feet (6 meters).
18. What is the primary technical issue created by an un-terminated (open) port on a coaxial splitter?
Excessive AC power is consumed by the splitter. The unused port introduces a high-impedance mismatch >75 Ohms, causing signal reflections (standing waves). The return path is completely blocked on all active ports. It filters out all frequencies below 54MHz.
19. If a cable modem registers an Upstream signal level that is too high (requiring the modem to 'shout'), the technician should investigate:
Downstream signals levels being too low. Too much passive loss between the modem and the CMTS. The presence of a 75 Ohm terminator on an active port. The headend is experiencing too much egress.
20. When troubleshooting coaxial cable, a common cause of intermittent signal loss that is not a hard fault (short or open) is:
Constant system-wide ingress from the headend. A crimped cable or 'kink' that alters the spacing of the center conductor/dielectric only when the cable moves. Corrosion in the connection that causes a temporary open circuit when wet. An active amplifier going into full overload.
21. What is the primary reason why a loose F-connector connection can cause severe ingress noise in the return path?
The loose connection acts as a low-pass filter, blocking high-frequency signals. A loose connection compromises the shield, allowing external, low-frequency broadcast signals to enter the cable. The modem increases its transmit power to compensate for the bad connection. It causes the cable's characteristic impedance to drop to 50 Ohms
22. Which problem is correctly solved by using a 75 Ohm terminator on an unused splitter port?
To block AC power from traveling into the customer equipment. To prevent an impedance mismatch that causes signal reflections back into the system. To reduce the signal loss (attenuation) of the splitter. To prevent ingress noise from entering the cable via the shield.
23. What should be done to the center conductor of a coaxial cable when preparing it for a connector termination?
It should be bent at a 90-degree angle to ensure a tight connection. It should be trimmed so that it is exactly flush with the end of the cable jacket. It must be kept clean, straight, and properly exposed beyond the dielectric to make full contact with the connector pin. It must be covered with dielectric grease to prevent corrosion.
24. Which type of loss in a drop line is dependent on the ambient temperature?
Insertion Loss of passive devices (splitters/taps) Loss due to signal reflection (Return Loss) Attenuation loss of the coaxial cable (higher temperature = higher loss) Loss due to the cable's permanent crimp or kink.
25. If a customer is experiencing slow, intermittent internet speeds, which two technical readings are most crucial to check first?
DC voltage level and cable type (RG-59 vs. RG-6). Signal Level (dBmV) and Modulation Error Ratio (MER) or Signal-to-Noise Ratio (SNR). The splitter brand and the color of the cable jacket. Cable length and the number of neighboring homes on the same tap.