Question
What power level does a receiver minimum discernible signal of -100 dBm represent?
Answer Options
- A) 100 microwatts
- B) 0.1 microwatt
- C) 0.001 microwatts
- D) 0.1 picowatts
Correct Answer: D
Explanation
The abbreviation dBm is a power ratio referenced to 1 milliwatt (mW). A value of 0 dBm equals 1 mW. To convert a negative dBm value (which represents a fractional mW) to watts, the formula is P_{W} = 10^{(P_{dBm}/10)} / 1000. This calculation reveals that the Minimum Discernible Signal (MDS) in amateur radio often represents an extremely small amount of power.
To find the power represented by -100 dBm, we calculate 10^{(-100/10)} mW = 10^{-10} mW. Since 1 mW is 10^{-3} W, 10^{-10} mW is 10^{-13} W. Using picowatts (pW) as the unit (1 pW = 10^{-12} W), 10^{-13} W = 0.1\times 10^{-12} W. Thus, -100 dBm represents a power level of 0.1 picowatts. This highlights the incredible sensitivity of modern amateur radio receivers.
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