In the described RF chain, what is the RF power level at the antenna input after amplification?

In the described RF chain, what is the RF power level at the antenna input after amplification?

• A. 50 mW
• B. 75 mW
• C. 100 mW
• D. 150 mW

Answer: (B)

Amplification increases power by a constant factor, called the gain. To find the power at the antenna input after amplification, you multiply the power entering the amplifier by the amplifier’s linear gain (which you get by converting the gain from dB to a linear ratio). In this scenario, the numbers imply the signal entering the amplifier is 30 mW, and the amplifier provides a gain of about 4 dB. A 4 dB gain corresponds to a linear factor of roughly 2.5 (since 10^(4/10) ≈ 2.5). Multiplying gives 30 mW × 2.5 = 75 mW. So the RF power at the antenna input after amplification is 75 mW. The other options would require different gain values: about 1.67× gain for 50 mW, about 3.33× for 100 mW, and about 5× for 150 mW. These do not match the described amplification in this chain, so they’re not correct.

Amplification increases power by a constant factor, called the gain. To find the power at the antenna input after amplification, you multiply the power entering the amplifier by the amplifier’s linear gain (which you get by converting the gain from dB to a linear ratio).

In this scenario, the numbers imply the signal entering the amplifier is 30 mW, and the amplifier provides a gain of about 4 dB. A 4 dB gain corresponds to a linear factor of roughly 2.5 (since 10^(4/10) ≈ 2.5). Multiplying gives 30 mW × 2.5 = 75 mW. So the RF power at the antenna input after amplification is 75 mW.

The other options would require different gain values: about 1.67× gain for 50 mW, about 3.33× for 100 mW, and about 5× for 150 mW. These do not match the described amplification in this chain, so they’re not correct.