SBCA System Maintenance 3 — Questions and Answers
Question 1: What is the purpose of a waveguide pressure window in a satellite uplink system?
- To amplify signal power
- To maintain pressurized dry air inside the waveguide and prevent moisture entry (Correct answer)
- To filter harmonics from the HPA
- To match impedance between the HPA and antenna
Correct answer: To maintain pressurized dry air inside the waveguide and prevent moisture entry
Waveguide pressure windows seal the waveguide system to keep it pressurized with dry nitrogen or air, preventing moisture from causing arcing or signal degradation.
Question 2: Which parameter is checked to verify that a high-power amplifier (HPA) is operating within its linear region?
- DC input voltage
- Output back-off (OBO) relative to the saturated power rating (Correct answer)
- LNB noise temperature
- Dish surface accuracy
Correct answer: Output back-off (OBO) relative to the saturated power rating
Output back-off measures how far below saturation the HPA is operating; maintaining adequate OBO ensures linear, interference-free amplification.
Question 3: During a scheduled maintenance window, a technician discovers that the BUC (Block Up-Converter) output power is 3 dB below spec. What should be checked first?
- Satellite ephemeris data
- DC power supply voltage and current draw of the BUC (Correct answer)
- IRD software version
- Antenna polarization skew
Correct answer: DC power supply voltage and current draw of the BUC
A 3 dB power drop often indicates a power supply issue, so verifying DC voltage and current is the first diagnostic step before replacing the BUC.
Question 4: What maintenance task is critical when replacing a feedhorn on a prime-focus dish?
- Updating the IRD subscription
- Re-peaking the antenna for maximum signal after feedhorn installation (Correct answer)
- Replacing the entire LNB assembly
- Reformatting the receiver hard drive
Correct answer: Re-peaking the antenna for maximum signal after feedhorn installation
After replacing a feedhorn, the antenna must be re-peaked to ensure the new feedhorn is correctly positioned at the focal point for maximum gain.
Question 5: A satellite dish's actuator motor moves the dish but the position sensor reports no change. What component has most likely failed?
- The IRD tuner
- The position sensor (reed switch or encoder) (Correct answer)
- The LNB power supply
- The demodulator board
Correct answer: The position sensor (reed switch or encoder)
If the motor operates but position feedback is absent, the position sensor (reed switch or optical encoder) that tracks dish movement has failed.
Question 6: When performing cable entry maintenance on an outdoor unit, what is the primary sealing method to prevent water ingress?
- Standard PVC electrical tape only
- Self-amalgamating (self-fusing) tape applied over weatherproof compound on all connectors (Correct answer)
- Silicone grease inside the connectors
- Heat-shrink tubing without adhesive
Correct answer: Self-amalgamating (self-fusing) tape applied over weatherproof compound on all connectors
Self-amalgamating tape creates a waterproof seal over weatherproofed connectors, preventing moisture ingress that could cause corrosion and signal degradation.
Question 7: What is the significance of monitoring HPA cathode current during satellite uplink maintenance?
- It indicates the satellite's orbital position
- It reveals the health of the traveling wave tube (TWT) and can predict impending failure (Correct answer)
- It measures downlink signal strength
- It shows the dish's pointing accuracy
Correct answer: It reveals the health of the traveling wave tube (TWT) and can predict impending failure
Cathode current trends in a TWT HPA are a key health indicator; a rising or erratic cathode current can predict tube degradation before complete failure.
SBCA System Maintenance 3
What is the purpose of a waveguide pressure window in a satellite uplink system?