From http://www.ivorcatt.co.uk/tony12.htm

Comments for Ivor Catt [by Tony Davies from five years ago]:

Filters

I will start by responding to your saying that you did not know what a passive filter was.   For sure

terminology can often be a problem and sources of deep misunderstandings.  More of that later. I give a

long answer, because much of my life has been in the Circuit Theory field, which has been a ‘foundation’

for my attitudes to other topics.

Historically I believe that Campbell was one of the first to develop the concept of what was then called a

‘wave filter’ – according to A.T. Starr (Electric Circuits and Wave Filters, Pitman, 1938), Campbell said: A

wave filter is a device for separating waves characterised by a difference in frequency.

Of course, all that they were thinking of was ‘steady state’ analogue telecommunications, no pulses or digital

technology.

It started with Heaviside’s circuit model [Note 1] (a cascade of Series L,R and parallel C, G elements) for a finite

length of uniform transmission, with increased accuracy as the circuit components becomes greater in

number and at the same time smaller in value – so that the real line was the limit of an infinite number of

infinitesimally small L,R,C,G components. From this model all the conventional ideas of characteristic

impedance, propagation constant, etc. and formulae for input impedance of terminated lines and so on all

follow.

….

Narrow band filter looking for 2kHz:

About your story of a very narrow band filter with a centre frequency of 2kHz, I believe anyone with any

experience and competence in classical filter design, old fashioned circuit theory etc, would know very well

that whatever the input signal to such a filter was, all that could come out in steady state conditions would be

a 2kHz sine wave.

Wrong. You should remove; “in steady state conditions”. All that can ever come out, regardless of input. Every input is turned into a 2kHz output. It uses all energy input to create 2kHz output.

….

Tony Davies

2017 April 4^th

Note 1. Here, Heaviside was dealing, not with theory, but with an imperfect, lossy transmission line.

The above is Wrong.

When a signal is inputted into a transmission line, the “impedance” it experiences is resistive. It has nothing to do with L,R,C,G . It sees Ω.

Here we see why Davies did not understand when electromagnetics rapidly switched from analog to digital in 1965.

Pythagoras is about a triangle with lines of zero width, with squares with lines of zero width. Similarly, the theory of the transmission line is of perfect conductors and dielectrics. It involves no L,R,C,G. It involves only Ω and c. The conductors and dielectric are perfect.

Does Tony have a completely different “story” when what he would call “DC” is sent down a transmission line? What does the “DC” signal make of the alleged Ls and Cs?

Catt and Davidson keep out of this entangled mess. http://www.ivorcatt.co.uk/x18j51.pdf They know that the energy can only travel at the speed of light. Each “sliver” of energy density does not know whether it is part of a sine wave. It knows nothing of what is, or may be, immediately ahead of it or behind it. When introduced to the entry to a transmission line, it sees a resistance Zo, not L and/or C. Once inside the transmission line, some of the energy density leaks out sideways into the “conductors”, as Guillemin says. Most carries on between the guiding conductors at the speed of light. All very simple, but kept away from all students and text books today. Jackson only sends a sine wave down a transmission line, replete with losses and complicated mathematics.

Ivor Catt 14.3.2022