SBCA System Troubleshooting & Maintenance 3 — Questions and Answers
Question 1: A satellite dish experiences intermittent signal loss only between 11 AM and 2 PM local time during certain months. What phenomenon is most likely responsible?
- Sun outage caused by solar interference when the sun aligns behind the satellite (Correct answer)
- Peak daytime electrical grid interference
- Thermal overload of the LNB during peak sunlight
- Atmospheric ducting increasing interference
Correct answer: Sun outage caused by solar interference when the sun aligns behind the satellite
Sun outages occur when the sun passes directly behind a geostationary satellite relative to the receive antenna, flooding it with solar noise.
Question 2: When testing coaxial cable continuity in a satellite system, a technician measures 0 ohms between center conductor and shield. What does this indicate?
- The cable is functioning normally
- A short circuit between the center conductor and shield (Correct answer)
- The cable impedance is correctly matched at 75 ohms
- DC power is flowing correctly to the LNB
Correct answer: A short circuit between the center conductor and shield
Zero ohms between center conductor and outer shield indicates a dead short, which will prevent signal transmission and may damage connected equipment.
Question 3: A DVB-S2 receiver locks onto a signal but immediately loses lock repeatedly. Which modulation/coding parameter mismatch is most likely causing this?
- Incorrect symbol rate entered in the receiver (Correct answer)
- Wrong LNB local oscillator frequency selected
- Incorrect satellite orbital position in receiver settings
- Wrong DiSEqC switch port selected
Correct answer: Incorrect symbol rate entered in the receiver
An incorrect symbol rate setting causes the demodulator to sample at the wrong rate, preventing stable carrier lock even when frequency is correct.
Question 4: What is the recommended method for waterproofing an outdoor F-connector on a satellite coaxial cable?
- Apply standard electrical tape only
- Use self-amalgamating tape over a weatherproof boot or wrap with self-fusing silicone tape (Correct answer)
- Apply silicone sealant directly into the connector threads
- Leave unsealed since F-connectors are weather-rated
Correct answer: Use self-amalgamating tape over a weatherproof boot or wrap with self-fusing silicone tape
Self-amalgamating or self-fusing silicone tape creates a waterproof seal around the connector without leaving adhesive residue that can trap moisture.
Question 5: A satellite technician is called to service a system where the IRD shows a signal but no audio is present on any channel. What is the most likely cause?
- Audio decoding format mismatch (e.g., Dolby AC3 with no license) (Correct answer)
- Incorrect satellite transponder frequency
- Faulty LNB causing signal degradation
- DiSEqC communication failure
Correct answer: Audio decoding format mismatch (e.g., Dolby AC3 with no license)
If video is present but audio is absent on all channels, an audio codec license issue (such as AC3/Dolby) or audio output configuration mismatch is the most common cause.
Question 6: During a site survey for a new VSAT installation, which tool is essential for determining dish pointing angles?
- A spectrum analyzer
- A satellite finder meter combined with a compass and inclinometer (Correct answer)
- A network protocol analyzer
- A time-domain reflectometer (TDR)
Correct answer: A satellite finder meter combined with a compass and inclinometer
A satellite finder provides real-time signal feedback while a compass sets azimuth and an inclinometer sets the elevation angle for dish alignment.
Question 7: What maintenance schedule is generally recommended for inspecting outdoor satellite dish mounting hardware in a harsh coastal environment?
- Every 5 years
- Annually at minimum, with quarterly visual checks recommended (Correct answer)
- Only when signal degradation is observed
- Once after initial installation
Correct answer: Annually at minimum, with quarterly visual checks recommended
Coastal salt air accelerates corrosion of mounting hardware, requiring more frequent inspection cycles than inland installations to prevent structural failures.
SBCA System Troubleshooting & Maintenance 3
A satellite dish experiences intermittent signal loss only between 11 AM and 2 PM local time during certain months.
What phenomenon is most likely responsible?