Question
What is the link margin in a system with a transmit power level of 10 W (+40 dBm), a system antenna gain of 10 dBi, a cable loss of 3 dB, a path loss of 136 dB, a receiver minimum discernable signal of -103 dBm, and a required signal-to-noise ratio of 6 dB?
Answer Options
- A) -8dB
- B) -14dB
- C) +8dB
- D) +14dB
Correct Answer: C
Explanation
Link margin is a quantitative measure of a communication system’s robustness. It is defined as the difference between the received signal level (what the receiver actually sees) and the minimum signal level required for acceptable communication. A positive link margin indicates reliable operation, while a negative margin indicates a performance failure.
The calculations performed show a received signal level (P_{RX}) of -89 dBm (40 dBm + 10 dBi - 3 dB - 136 dB). The minimum required signal level (S_{Req}) is -97 dBm (-103 dBm + 6 dB). The link margin is therefore +8 dB (-89 dBm - (-97 dBm)). This positive value means the received signal exceeds the minimum requirement by 8 dB and the link is highly robust.
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