Re: Actual effect of lossy component on physical noise power
It is true that a 3 dB attenuator will attenuate both signal and noise present at its input by the same amount (3 dB). However any noise introduced after the attenuator will now have a 3 dB advantage over the signal, thus the potential drop in signal-to-noise ratio. For example, many advanced short wave radios have a switchable attentuator at their inputs. This is to allow reducing the level of strong signals which can overload the radio's front end. However, for normal strength signals, the attentuator is not used because it reduces the incoming signal level which effectively amplifies the effect of the radio's internal noise (which is not important for very strong signals).
Theory says that any resistance generates noise which, among other variables, varies as the square root of the absolute temperature. For any given noise source, an equivalent noise temperature is the temperature of a resistance equal to the noise source which theoretically generates the same level of noise.