Standing alone, yes, decibels are ambiguous. But decibels are as ambiguous as saying "times two" without referencing what you're doubling. There should always be a reference.

The gain listed in dB is referring to the input type. So...

What's your input?

I'm not sure I've seen something as ambiguous as a device called "amplifier" with its gain in dB and no other information. You'll usually have a voltage amplifier or a current amplifier; an amplifier with the input being voltage or current respectively. That is, if you have a voltage amplifier, then the input is voltage and the output is the voltage with gain. A voltage amplifier with 3dB gain will turn a 1V input into 1.4125V (0dBV to 3dBV).

If your input is dBm, then the input is power, and the output is power with gain. For your example, a device with a 0 dBm input and a +3dB gain, the output will with 3dBm. Similarly, if the input is 0dBW the output will be 3dBW.

Standing alone, yes, decibels are ambiguous. But decibels are as ambiguous as saying "times two" without referencing what you're doubling. There should always be a reference.

The gain listed in dB is referring to the input type. So...

What's your input?

I'm not sure I've seen something as ambiguous as a device called "amplifier" with its gain in dB and no other information. You'll usually have a voltage amplifier or a current amplifier; an amplifier with the input being voltage or current respectively. That is, if you have a voltage amplifier, then the input is voltage and the output is the voltage with gain. A voltage amplifier with 3dB gain will turn a 1V input into 1.4125V (0dBV to 3dBV).

If your input is dBm, then the input is power, and the output is power with gain. For your example, a device with a 0 dBm input and a +3dB gain, the output will be 3dBm. Similarly, if the input is 0dBW the output will be 3dBW.

The gain listed in dB is referring to the input type. So...

What's your input?

I'm not sure I've seen something as ambiguous as a device called "amplifier" with its gain in dB and no other information. You'll usually have a voltage amplifier or a current amplifier; an amplifier with the input being voltage or current respectively. That is, if you have a voltage amplifier, then the input is voltage and the output is the voltage with gain. A voltage amplifier with 3dB gain will turn a 1V input into 1.4125V (0dBV to 3dBV).

If your input is dBm, then the input is power, and the output is power with gain. For your example, a device with a 0 dBm input and a +3dB gain, the output will with 3dBm. Similarly, if the input is 0dBW the output will be 3dBW.

Standing alone, yes, decibels are ambiguous. But decibels are as ambiguous as saying "times two" without referencing what you're doubling. There should always be a reference.

The gain listed in dB is referring to the input type. So...

What's your input?

I'm not sure I've seen something as ambiguous as a device called "amplifier" with its gain in dB and no other information. You'll usually have a voltage amplifier or a current amplifier; an amplifier with the input being voltage or current respectively. That is, if you have a voltage amplifier, then the input is voltage and the output is the voltage with gain. A voltage amplifier with 3dB gain will turn a 1V input into 1.4125V (0dBV to 3dBV).

If your input is dBm, then the input is power, and the output is power with gain. For your example, a device with a 0 dBm input and a +3dB gain, the output will with 3dBm. Similarly, if the input is 0dBW the output will be 3dBW.