From time to time I see online discussion about determining matched line loss (MLL) from Return Loss.
Something like 150 years ago a self educated genius thought about the problem of ‘smearing’ of telegraph signals in submarine cables and developed a model for the behavior of transmission lines that remains a very good model today. (The guy’s day job was as a telegraphist.)
He needed to develop new mathematics and new concepts like reactance, and he did this in the face of recognised engineers of the day dismissing the ideas.
The smearing problem was different propagation speed of the fundamental and harmonic components of the telegraphy waveform, he referred to it as distortion and in terms of his RLGC transmission line model he defined the requirements for a “Distortionless Line”. Zo for a Distortionless line is a purely real number, and a Lossless Line is a special case of a Distortionless Line. Continue reading RF transmission lines – quite old art