TIL that a lot of people who think they understand decibels don’t realize that there are different scales for amplitude (volts), where a factor of 10 is 20dB, and for power (watts),where a factor of 10 is 10dB ). It’s confusing, but part of what makes dBs useful.
Why? Because it enables sorcery where once you measure ratio and convert to dB (whether with volts or Watts), the same dB values are useful for calculations in either.
In other words, suppose I have a circuit that attenuates volts. I measure 1 volt going in and 0.1 volts coming out. That’s a 20 dB attenuation.
Now I can take this 20 dB attenuator and calculate that if I put 1 Watt in, I’ll get 0.01 Watts out (a 20dB reduction in power).
Now I can take this 20 dB attenuator and calculate that if I put 1 Watt in, I’ll get 0.01 Watts out (a 20dB reduction in power).
I swear I am not lying to you about decibels.
Anyway, another reason RF engineers like dBs is that you can just add them together. Amplifiers add dBs and attenuators subtract them. So if you take the output of 10dB attenuator and put it into a 30 dB amplifier, you’ve built a 20dB amplifier.
RF engineers know their dB calculations the way computer scientists know powers of 2.
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