SBCA System Troubleshooting & Maintenance 2 — Questions and Answers
Question 1: A satellite receiver shows a signal strength of 85% but signal quality drops to 20% during rain. What is the most likely cause?
- Faulty LNB power supply
- Rain fade causing signal attenuation on Ku-band frequencies (Correct answer)
- Misaligned dish azimuth
- Defective coaxial cable connector
Correct answer: Rain fade causing signal attenuation on Ku-band frequencies
Rain fade is a well-known phenomenon where precipitation absorbs and scatters Ku-band signals, reducing signal quality even when the carrier is detected.
Question 2: When performing a spectrum analyzer sweep on a satellite transponder, you observe a raised noise floor across the entire bandwidth. What does this typically indicate?
- A strong desired signal is overdriving the LNB
- Uplink interference or transponder overload from excess carrier power (Correct answer)
- The spectrum analyzer's reference level is set too low
- A single interfering carrier on an adjacent transponder
Correct answer: Uplink interference or transponder overload from excess carrier power
A raised noise floor across a full transponder typically indicates uplink interference or an overdriven transponder from excess carrier power.
Question 3: A VSAT terminal suddenly loses two-way communication but can still receive broadcast channels. Which component is most likely faulty?
- The receive LNB
- The indoor unit (modem) receive card
- The transmit BUC (Block Upconverter) (Correct answer)
- The dish feed horn
Correct answer: The transmit BUC (Block Upconverter)
Since receive functionality is intact, the transmit BUC is the most likely failed component preventing two-way communication.
Question 4: What does a C/N (Carrier-to-Noise) ratio measurement indicate in satellite link analysis?
- The ratio of carrier power to thermal noise power in the receiver bandwidth (Correct answer)
- The ratio of uplink power to downlink power
- The number of carriers occupying a transponder
- The signal attenuation caused by the atmosphere
Correct answer: The ratio of carrier power to thermal noise power in the receiver bandwidth
C/N ratio expresses how much stronger the desired carrier signal is compared to the thermal noise floor, directly impacting demodulation performance.
Question 5: During routine maintenance, a technician finds the dish elevation has drifted 2 degrees below the optimal setting. What is the most likely cause on a fixed mount?
- Thermal expansion and contraction cycles loosening mount bolts (Correct answer)
- Increased satellite orbital inclination
- Uplink power reduction from the satellite operator
- Atmospheric refraction shifting apparent satellite position
Correct answer: Thermal expansion and contraction cycles loosening mount bolts
Thermal cycling causes metal mounting hardware to expand and contract, gradually loosening bolts and allowing dish position to drift.
Question 6: A headend operator notices BER (Bit Error Rate) increasing gradually over several weeks without any weather events. What should be checked first?
- Satellite orbital slot change by the operator
- LNB gain degradation or connector corrosion at the feedhorn (Correct answer)
- Transponder frequency plan change
- IRD firmware update requirement
Correct answer: LNB gain degradation or connector corrosion at the feedhorn
Gradual BER degradation without weather correlation typically points to slow-onset issues like LNB aging, internal corrosion, or connector oxidation.
Question 7: What is the primary purpose of a satellite link budget calculation during troubleshooting?
- To determine the cost of satellite bandwidth
- To calculate expected signal margins and identify where losses exceed design parameters (Correct answer)
- To schedule maintenance windows with the satellite operator
- To measure actual transponder output power
Correct answer: To calculate expected signal margins and identify where losses exceed design parameters
A link budget analysis compares expected vs. actual signal levels at each stage, helping isolate where losses are exceeding design margins.
SBCA System Troubleshooting & Maintenance 2
A satellite receiver shows a signal strength of 85% but signal quality drops to 20% during rain.
What is the most likely cause?