Which statement correctly describes a satellite transponder used in communications satellites?
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AIt contains a receiver and a transmitter designed to relay microwave transmissions from one point on earth to another.
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BIt simply echoes received radiation without change from one point on earth to another.
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CIt transforms the message code to a different coding scheme before transmission to earth.
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DIt receives at a lower frequency from earth stations and retransmits at a higher frequency to earth stations.
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ENone of the above
Answer
Correct Answer: It contains a receiver and a transmitter designed to relay microwave transmissions from one point on earth to another.
Explanation
Introduction: A satellite transponder is the fundamental “bent-pipe” element aboard a communications satellite. It listens to uplink signals, conditions them (filtering, frequency translation, amplification), and retransmits them back toward earth on a designated downlink frequency. Understanding this basic operation helps differentiate correct and incorrect statements about satellite links.
Given Data / Assumptions:
- We consider a conventional bent-pipe communications satellite (not regenerative on-board processing).
- Standard operation involves receive chain, frequency conversion, amplification, and transmit chain.
- Uplink and downlink use different frequency bands to avoid interference.
Concept / Approach: A transponder includes a receiver (LNA, filtering), a frequency converter/translator, and a power amplifier feeding the transmit chain. It does not “echo” without change; it performs translation and amplification. Also, for most services, the satellite receives at a higher uplink frequency and transmits at a lower downlink frequency (e.g., C-band, Ku-band), contrary to the misleading claim about the direction of frequency change.
Step-by-Step Solution:
1) Identify required blocks: receiver + translator + transmitter.2) Recognize purpose: relay (bent-pipe) from uplink beam to downlink beam.3) Compare options: only the statement describing RX + TX relay fits universally.Verification / Alternative check: Industry diagrams show transponders converting uplink to a different downlink frequency while applying gain and filtering, confirming the receiver-transmitter characterization.
Why Other Options Are Wrong:
- Echo without change: ignores frequency translation and amplification.
- Transforms code: regenerative satellites can process, but basic transponders do not change message coding.
- Lower RX, higher TX: reversed; satellites typically receive higher-frequency uplinks and transmit lower-frequency downlinks.
- None of the above: one option is correct.
Common Pitfalls: Assuming satellites behave like passive mirrors; confusing regenerative processing with bent-pipe relaying.
Final Answer: A satellite transponder contains a receiver and a transmitter that relay microwave transmissions between earth stations.