SSPI Satellite Communications Technologies & Systems 5

Question 1

What is the primary purpose of Forward Error Correction (FEC) in a satellite communications system?

Accepted Answer

Add redundant bits to allow the receiver to detect and correct errors without retransmission

Answer

FEC codes (e.g., Turbo codes, LDPC) add calculated redundancy so the receiver can reconstruct corrupted bits, crucial for one-way broadcast links where retransmission is impractical.

Question 2

A satellite in a Molniya orbit is specifically designed to provide extended coverage over which geographic regions?

Accepted Answer

High-latitude polar and sub-polar regions

Answer

Molniya orbits (63.4° inclination, ~12-hour period) spend most of their time at high apogee over the northern latitudes, providing long dwell times over Arctic and high-latitude areas.

Question 3

What is 'intermodulation distortion' in a satellite transponder, and when does it become most severe?

Accepted Answer

Nonlinear mixing of multiple carriers in an amplifier; worst when operating near saturation

Answer

When multiple carriers share a nonlinear amplifier near saturation, their mixing products create intermodulation (IM) products that interfere with adjacent carriers; output back-off reduces but doesn't eliminate IM.

Question 4

In the context of satellite communications, what does 'orbital debris mitigation' require of GEO satellites at end of life?

Accepted Answer

Boost to a graveyard orbit at least 300 km above GEO

Answer

ITU and national regulations require end-of-life GEO satellites to be boosted to a graveyard orbit ≥300 km above GEO (≥36,086 km) to protect the operational GEO belt.

Question 5

What advantage does Direct Broadcast Satellite (DBS) service have over traditional FSS (Fixed Satellite Service) in the context of consumer reception?

Accepted Answer

DBS uses higher EIRP spot beams enabling small (45–90 cm) consumer dishes

Answer

DBS transponders transmit at high power in concentrated spot beams, allowing households to receive signals with small, inexpensive fixed dishes rather than large C-band dishes.

(SSPI) Society of Satellite Professionals International Certification Practice Test

(SSPI) Society of Satellite Professionals International Certification Practice Test

SSPI Satellite Communications Technologies & Systems 5