Satellite Theory & Signal Transmission Flashcards

In satellite forward error correction (FEC), what does a code rate of 3/4 mean?

Answer: For every 4 bits transmitted, 3 are information bits and 1 is redundancy

A 3/4 code rate means 3 information bits are transmitted for every 4 bits on the channel; the additional bit is redundancy used for error correction at the receiver.

What is the effect of increasing the symbol rate (baud rate) of a satellite carrier while keeping the transponder bandwidth constant?

Answer: The carrier eventually exceeds the transponder bandwidth, causing adjacent channel interference

Symbol rate and bandwidth are directly related; increasing symbol rate beyond the transponder bandwidth causes spectral spillover and interference to adjacent carriers.

Which type of satellite orbit is used by GPS, Galileo, and Glonass navigation systems?

Answer: Medium Earth Orbit (MEO)

Navigation constellations use MEO at approximately 19,000–24,000 km altitude, providing global coverage with relatively few satellites compared to LEO.

In satellite link budgets, free-space path loss (FSPL) increases with what two parameters?

Answer: Frequency and distance

FSPL (dB) = 20log(d) + 20log(f) + 92.44 (for km and GHz), showing that higher frequency and greater distance both increase path loss.

What is the purpose of a low-noise block downconverter (LNB) in a satellite receive system?

Answer: Amplify the weak satellite signal and convert it to a lower intermediate frequency with minimal added noise

The LNB amplifies the downlink signal at the dish focal point and frequency-converts it to an L-band IF (950–2150 MHz) for transmission over coaxial cable to the indoor receiver.

Frequency reuse in satellite systems allows the same frequency band to be used multiple times by exploiting which technique(s)?

Answer: Orthogonal polarizations and/or spatially separated spot beams

Satellites reuse spectrum by separating signals with orthogonal polarizations (horizontal/vertical or left/right circular) and with geographically isolated spot beams that limit interference.

What is a geosynchronous satellite, and how does it differ from a geostationary satellite?

Answer: Geosynchronous matches Earth's rotation period but may have non-zero inclination; geostationary is also equatorial

All geostationary satellites are geosynchronous, but geosynchronous satellites with non-zero inclination trace a figure-8 ground track (analemma) instead of remaining fixed over one point.