The purpose of this web page is to discuss the meanings of the English words GAIN and LOSS, which are often met in dealing with electronic systems, antennas, and so on.
If I weigh 100 kg and experience a gain of 1 kg, my weight becomes 101 kg. It is understood that by the word "gain" we imply the process of adding 1 kg.
If I weigh 100 kg and experience a loss of 1 kg, my weight becomes 99 kg. It is understood that by the word "loss" we imply the process of subtracting 1 kg.
Let me put a question to you. Suppose I have an electronic circuit whose power loss is 10 dB. Would you say that the output power is larger than, or smaller than, the input?
And let me put the other side of the question; if the circuit has a power gain of 10 dB, is the output larger, or smaller, than the input.
Now let me ask you what size the output power will be, compared to the input, if you are told that the gain is -10 dB?
And finally, if the loss is -10 dB?
My solution is that "loss" of 10 dB is "gain" of -10 dB (and that conversely, "gain" of 10 dB is "loss" of -10 dB). This way, we have a consistent use of nomenclature.
How many times have you seen the words such as "return loss of -20 dB" to describe a returned signal which is 1/100th of the incident signal?
I would call this situation a "return loss of 20 dB" or a "reflection coefficient of -20 dB"
Copyright © D.Jefferies 2001.