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An amplifier has small-signal gain 15 dB and 1-dB gain compression at an input power of 13.2 dBm. The amplifier is used to amplify four modulated signals of equal power. To avoid problems with intermodulation products, the amplifier will be operated at least 5 dB below the 1-dB gain compression point. What is the maximum output power of each signal?

My workings:
1-dB compression point: 15 dB - 1 dB = 14 dB
5 dB below this value: 14 dB - 5 dB = 9 dB
5 dB below the input power: 13.2 dBm - 5 dB = 8.2 dBm
Divide by 4 input powersL 8.2 dBm - 6 dB = 2.2 dBm
Max output power: Gain + input power = 9 dB + 2.2 dB = 11.2 dB

Is this correct?

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  • \$\begingroup\$ Why do you think a gain 5 dB below the gain with 1 dB compression (your 2nd equation) is relevant? \$\endgroup\$
    – The Photon
    Commented Oct 31, 2017 at 2:56

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I'd work it like this:

The 1 dB compression input power is 13.2 dBm

5 dB below this is 8.2 dBm

You have 4 equal-power inputs, so each must have 1/4 of this much power to avoid compression,

8.2 dBm - 6 dB = 2.2 dBm

This is the input power you'll be operating at. The output power for each signal will be

2.2 dBm + 15 dB = 17.2 dBm

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  • \$\begingroup\$ What about instantaneous summation of the various sinusoids? \$\endgroup\$ Commented Oct 31, 2017 at 15:11

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