SBCA System Maintenance 4 — Questions and Answers
Question 1: What is the purpose of a redundancy switch (1:1 or 1:N) in a satellite uplink facility?
- To split the signal between two satellites simultaneously
- To automatically switch to a backup HPA or LNB if the primary unit fails (Correct answer)
- To combine signals from multiple satellites
- To filter out-of-band interference
Correct answer: To automatically switch to a backup HPA or LNB if the primary unit fails
Redundancy switches automatically route the signal path through a backup unit when the primary fails, maintaining continuous operation.
Question 2: A technician is tasked with cleaning a satellite dish surface. Which cleaning agent should be avoided to prevent surface degradation?
- Mild soap and water
- Solvents containing acetone or MEK (methyl ethyl ketone) (Correct answer)
- Deionized water with a soft brush
- Isopropyl alcohol at low concentration
Correct answer: Solvents containing acetone or MEK (methyl ethyl ketone)
Acetone and MEK-based solvents can dissolve painted surfaces and damage protective coatings on reflector dishes, leading to long-term corrosion.
Question 3: Which maintenance activity is recommended to prevent intermodulation distortion in a multi-carrier satellite system?
- Increasing all carrier power levels
- Properly setting output back-off levels and verifying carrier power ratios (Correct answer)
- Disabling the automatic level control (ALC)
- Bypassing the bandpass filter
Correct answer: Properly setting output back-off levels and verifying carrier power ratios
Proper output back-off and carrier power management ensures the HPA operates in a linear range, minimizing intermodulation products between carriers.
Question 4: During a VSAT network maintenance window, the NOC reports elevated BER on several remotes. All remotes use the same hub. What should the maintenance team investigate first at the hub?
- Individual remote dish alignments
- Hub HPA output power and uplink carrier quality (Correct answer)
- Remote site power supplies
- Remote IRD software versions
Correct answer: Hub HPA output power and uplink carrier quality
If multiple remotes show elevated BER simultaneously, a hub-side issue such as reduced HPA power or degraded uplink is the most likely common cause.
Question 5: What is the function of an automatic level control (ALC) circuit in a satellite uplink chain?
- To control dish rotation speed
- To maintain constant output power from the uplink chain despite input signal variations (Correct answer)
- To decrypt conditional access signals
- To monitor downlink frequency stability
Correct answer: To maintain constant output power from the uplink chain despite input signal variations
ALC circuits automatically adjust gain to compensate for rain fade or input variations, maintaining a stable uplink power level at the satellite.
Question 6: A satellite technician notices the noise figure of a receive system has degraded by 2 dB since the last maintenance. Which component is most likely responsible?
- The IRD's MPEG decoder
- The LNB, as it is the first active element and dominates system noise figure (Correct answer)
- The bandpass filter after the LNB
- The power splitter at the IRD input
Correct answer: The LNB, as it is the first active element and dominates system noise figure
The LNB is the first active component in the receive chain and contributes most to the overall system noise figure, so LNB degradation has the greatest impact.
Question 7: When documenting satellite system maintenance activities, why is it important to record baseline signal level measurements?
- To comply with FCC frequency allocation rules
- To establish a reference for detecting future degradation and trending performance over time (Correct answer)
- To set the IRD video output resolution
- To program the dish actuator limits
Correct answer: To establish a reference for detecting future degradation and trending performance over time
Baseline measurements allow technicians to identify trends, detect gradual degradation, and distinguish normal system variation from emerging faults.
SBCA System Maintenance 4
What is the purpose of a redundancy switch (1:1 or 1:N) in a satellite uplink facility?