Talk:Ivor Catt/Archive 5

Discussion on letter content

I tend to agree that the D s should not exist-- at all! (not even at the step). That's because I believe that nothing flows from one conductor to the other in a capacitor or TL. Energy flows along the line -that is all. This question of infinitesemal rise time is not relevant to the problem. How does your view differ from this?--Light current 23:21, 10 January 2006 (UTC)

The easiest fix is to pretend that the D's are E's, so that the arrows represent the electric field. Obviously, E is changing where the step is, so there is some displacement current there as well. Exactly what the displacement current is doing doesn't matter. Perhaps we should just coin the verb "to maxwell", which is defined to be what displacement current does....

What do you mean by the term displacement current?--Light current 02:15, 11 January 2006 (UTC)

I don't think I mean anything by it other than "This is a situation where Maxwell's correction of Ampere's equation is important." We're still waiting for the physicists to finally decide exactly what "charge" and "electric field" and "magnetic field" actually are. In the meantime we can just stick the numbers into the formulae and use the results. -- Kevin Brunt 15:00, 11 January 2006 (UTC)

The point about dE/dt happening where the step is has been there ever since Catt, etc, first advanced the transmission line argument. It is part and parcel of moving from a point capacitance to one where the capacitance is dstributed evenly along a line. The step marks the point where the actual charging of the capacitor is happening. Overall the total amount of "dE/dt" ought to be determined only by the final voltage and the total capacitance.

Nigel's references to "radio emission" and "radio energy" are introducing a new complication. The normal use of the term "radio" would be to refer to transverse electromagnetic waves, which are self-sustaining "things" which travel at the speed of light, and which are very precisely defined by physicists. Nigel does not appear to have done any of the work needed to demonstrate that what is going on around the conductor conforms to the definition of a TEM wave. There seems to be an implication in what he's written that displacement current is TEM. This is certainly not the case; TEM is a very specific set of circumstances. Maxwell's mathematical insight allowed him to spot that the "TEM equations" were compatible with what we now call "Maxwell's Equations". He was probably gobsmacked when he realised that he was predicting a velocity of propagation virtually identical to the speed of light. I will not, however, believe that Maxwell ever claimed that everything with "displacement current" had to be TEM. Nor did he have a "radio theory"; that is tangling his work up with that of Hertz, and particularly Marconi. Nigel is creating a false picture. -- Kevin Brunt 02:00, 11 January 2006 (UTC)

I tend to agree with all of your last paragraph Kevin--Light current 02:15, 11 January 2006 (UTC)

I should also have added that Nigel's "radio emission" has a lot in common with Ivor Catt's original references to a "TEM step". The diagram clearly shows although there is undeniably something "electromagnetic" going on in and around the conductors, there is clearly current flow in the conductor (ie moving charge), which is in contradiction with the TEM equations which have no charge, but only (changing) electric and magnetic fields. Furthermore, the diagram clearly shows that the "em" involved is a result of the applied voltage; Catt's question starts "when a TEM step". Catt is thus placing the "TEM" as the "primary thought". He thinks that the voltage step and the "TEM step" are synonymous, a proposition that is at variance with his diagram. This is actually what the Catt Anomaly really is. -- Kevin Brunt 15:00, 11 January 2006 (UTC)

Kevin and Light Current: I have built various radio projects and also understand the maths of radio emission. There is evidence that this is the sideways effect from each conductor to the other which determines the speed of electricity (electric step goes at the average speed of the medium between the two conductors, as measured on sampling oscilloscopes). I'm talking of the physical mechanism. You aren't going to understand electricity without getting to the facts of what is really occurring. If displacement current is identical to the radio emission effect, then that is very significant. Radio induces currents. If each conductor is transmitting to the other, it would explain how currents arise! When the electric field is varying (increasing in the 0 to v volt step) you get varying current, and this emits radio waves in the direction perpendicular to the current, i.e., in the direction of so-called "displacement current". What part of this can't you grasp? Thank you very much for your opinions that the facts presented properly introduce "clutter" or present a "false picture". The fact is the opposite. You can politically ignore these facts (as Catt does) but that is not being scientific. I don't have to admit that more work needs to be done, because that's what I've been asking for for many years. By the way, Kevin, it was Heaviside in 1875 who did the TEM work, Maxwell's didn't do that many electrical experiments (he relied on reading Faraday's Experimental Researches and doing maths about an elastic aether, etc.) 172.202.239.245 15:18, 19 January 2006 (UTC)

Yes, Nigel, a fast voltage edge travelling down a conductor is likely to generate electromagnetic interference. You cannot, however, assume that the orientation of the generated fields will be the same as that produced by a sinusoidal voltage/current applied to a "resonant" conductor. Catt's diagram applies to a voltage pulse of any duration, and the correct "scientific" method of analysis should be consider the "steady-state" cases before and after the step in order to understand them properly, before going onto the more complex problem of understanding what is happening where the voltage is actively changing. Catt's work, and yours, fails entirely to deal with the "DC case" properly, and is seriously flawed thereby.

Catt's diagram, (and his "Electromagnetism" book,) both show clearly that for all his assertions that he has disposed of "charge", his "TEM wave" actually comprises the electric and magnetic fields due to the charge in the capacitance conductor and the motion of the charge (ie current) in the inductance. Hence Catt's "wave" is created by the charge in the conductor. Therefore, it cannot, by definition, be a self-sustaining "vibration" in "free space" as is meant by physicists when they use the term "transverse electromagnetic wave". Catt is using the term "TEM" for something other than the "agreed meaning", and the "Catt Anomaly" is merely the confusion caused thereby. Ask a silly question, get a silly answer.

Incidentally, it ought to be obvious that as well as there being a changing electric field between the conductor at the point where the voltage step is (perpendicular to the conductor), that there is a changing electric field in front of the step in the direction of the conductor. Whatever the displacement current is doing, it is not merely doing it in a straight line between the conductors, but is doing it in three dimensions around the point on the conductor that the voltage step has currently reached! -- Kevin Brunt 22:08, 19 January 2006 (UTC)

20 January 2006

Kevin: before the TEM step arrives at any part of the cable, there is zero voltage. As it arrives, the voltage increases and with it the current. Once it has peaked, it remains steady. The only period of interest is while the voltage is rising. Ivor ignores this, and also introduces other errors like the claim that displacement current flowing where the voltage is steady. Your sine wave radio signal versus square wave logic step argument is vacuous, since radio emission occurs so long as di/dt is not zero in any part of the aerial. Fourier analysis is useful to me for the purpose of translating a plot of current or field strength versus time into a frequency spectrum. According to Fourier analysis, you can represent a square wave as a series of sine waves! But that's not my main argument.

Consider the 2 conductor transmission lines as 2 parallel radio aerials. If you feed one with a signal (of any type) and leave the other passive, the first transmits energy to the passive one which receives energy only as a result of di/dt in the first one. This is indistinguishable from Maxwell's "displacement current" equation. Maxwell says vacuum "displacement current" i = e.dE/dt = e.dv/(x.dt) where e is permittivity and x is the width over which the step rises (definition: x = ct, where t is the rise-time). We see that if x = 0, then i = infinity. This disproves the idea of a truly abrupt step. Moreover, the current rises over the rise-time from 0 to its peak, and since radio emission occurs in proportion to di/dt, it becomes more intense as the step rise-time is made smaller.

Now here is the proof. Taking the 2 parellel aerials or transmission line conductors. Feed one with any signal, and feed the other with the inversion of that signal. While the signal strength rises, electrons accelerate and radio emission occurs in a perpendicular direction.

I've done this experiment and proved it experimentally. During the rise-time, each conductor transmits a radio signal that is the exact opposite of that emitted from the other conductor. At a long distance (several times the distance of the gap between the two conductors) there is no observable radio transmission at all, because each radio emission cancels out that of the other: perfect interference. (The same concept is often used as white noise to suppress sounds, but that is less effective.)

The point is that the entire radio energy emitted by each conductor during the step is transmitted to, and received by, the other conductor. This is the process by which the TEM wave is allowed to propagate. Catt, ironically, gives the conventional textbook slab of drivel on this point! See [1] (that web version misses out the formulae, but they are widely known) where Catt calculates the inductance of a single wire and finds: "The self inductance of a long straight conductor is infinite. This is a recurrence of Kirchhoff's First Law, that electric current cannot be sent from A to B. It can only be sent from A to B and back to A." I think it is unhelpful for Catt, having defined E and B in fixed ratio for a TEM wave (E=cB), then goes along with the unfruitful textbook treatment of inductance which considers inductance as a B field effect! The magnetic field loops around each conductor instead of going from one conductor to the other line "displacement current" or in fact radio energy. This is probably where the conventional theory went wrong! It is clear that the entire energy needed to propagate the TEM wave is transmitted as radio from one conductor to the other during the step. No loss occurs because the step in each is inverted with respect to the other in a TEM wave. I'm going to do the calculations to demonstrate how this solves the Catt anomaly. 172.209.113.91 20:52, 20 January 2006 (UTC)

Nigel, you cannot inject RF into one conductor independent of the other. The RF energy must flow in the dielectric. Or dont you believe in the Poynting vector?--Light current 22:59, 20 January 2006 (UTC)

Light current, radio is a fact. The Poynting vector is wrong in the way it is usually taken to suggest that nothing moves except in the propagation direction. The electric field vector, at right angles to the propagation (c labelled) vector also involves energy flow, hence the transverse nature of the wave. Catt interprets Heaviside and Poynting as a longitudinal wave, simply because they don't say anything about the transverse action.

The Poynting vector falsely omits transverse motion of energy: see the illustrated discussion on the blog here: [2]. 172.214.92.156 08:35, 21 January 2006 (UTC)

So, Nigel you are saying that vector calculus has been wrong all these years and so has Mr Poynting? You must publish this ASAP! Im sure it will be of interest to everyone!--Light current 02:15, 22 January 2006 (UTC)

Sideways energy flow?

If energy does flow in the direction of the electric (or magnetic) field in a coax cable ( ie radially from inner to outer ), where does this energy go when it hits the outer conductor? Also if this were true, you would be able to inject RF power into one end of a coax with a perfect termination at the other end, and find that some energy had been lost due to radial propagation. I dont believe any results of such an experiment have yet been published. But maybe you know different?--Light current 19:23, 21 January 2006 (UTC)

21 Jan 2006

Nigel has, I fear, opened several new cans of worms. Catt's diagram is, (for all of his denial of the existence of charge), entirely about current flowing in a conductor. If you were to take a TL, terminate it with a resistor that matched the TL's impedance and stick a battery across the open end, Catt's "TEM wave" represents the flow of energy out of the battery, through the TL and into the resistor. This is about what happens after the edge (or between the leading and trailing edges!) not what happens at the edge itself. For a complete pulse, the energy delivered into the resistor is the integral of the instantaneous product of the voltage and current over the duration of the pulse; the shape of the pulse is irrelevant. If there is "radio emission" at the edge, this would manifest as an electromagnetic wave carrying energy away from the conductor; this would reduce the "area under the curve", no doubt by taking the "corner" off the step and slowing the rise time.

I agree with you here Kevin.- the electromagnetic disturbance ceases (to an external observer) when the cable is fully charged to the on load source voltage! But why should em waves suddenly stop- what is the mechanism of stopping them?- That is Catts question--Light current 00:22, 21 January 2006 (UTC)

The fixation with the "edge" is a large part of Catt's "Electromagnetism" altogether. Basically, Catt, and Nigel, and Arnold Lynch, are unable to come to terms with how the motion of the "abstract" charge that is "current" can be explained in terms of the motion of the electrons in the conductor. Now I will agree that it is not well explained in "electricity" text books, but that is because it's not really part of electricity, but rather of "solid-state physics" with a lot of quantum mechanics thrown in. Electrical engineers need to know that the electrons are not moving down the conductor at the speed of light, but they can understand Ohm's Law without needing a postgraduate qualification in quantum mechanics as a pre-requisite!

Im afraid I dont agree that charge carriers can travel at the speed of light- but of course an EM wave can!. The only question is, what is an em wave made of ?. --Light current 00:22, 21 January 2006 (UTC)

-- I think this rather depends on exactly what you mean by "EM" and "wave". A rummage in Google suggests that what's propagating at light speed is the electric field due to the applied voltage, with the electrons following on afterwards. This is not unreasonable; applying simple theoretical mechanics to the "DC case" yields a model where the electrons move as a rigid mass at the electron drift velocity (which is proportional to current) which yields a very clear association in the model between voltage and force. (Nigel, of course, always leaves out the forces when tries this, and comes up with a entirely irrelevant conclusion about the kinetic energy stored in the electrons.) Whether the propagating field constitutes an "EM wave" is a matter of terminology. It may well just be "displacement current". -- Kevin Brunt 03:37, 21 January 2006 (UTC)

If there is coupling between two conductors in close proximity which reduces rapidly with distance, it is entirely possible that there is a capacitive or inductive explanation. -- Kevin Brunt 00:08, 21 January 2006 (UTC)}

My theory is that there is some sort of induced effect in two wires of a twin conductor TL but this is entirely due to the EM energy flowing between them down the dielectric! Poyntings vector again. Do you believe in it?--Light current 00:22, 21 January 2006 (UTC)

My own view is that what's propagating at light speed is the electric and magnetic fields due to the applied voltage, with the electrons following on afterwards as fast as they can. However, I dont call this displacement current, I call it energy current or em energy. You see, there must be some coming together of em field theory at high freq and circuit theory at low freq/dc. This can only be achieved by assuming that whenever physical charges cannot move fast enough, the em wave takes over and makes up the difference to present the ultra fast rise times that weve all? witnessed. BTW can you go back to sequential posting rather than interleaved, as its very confusing when the posts get out of chron order (esp with 3 respondent).--Light current 03:48, 21 January 2006 (UTC)

My aside about "displacement current" was merely to point up that there is a lot going on. The point about "circuit theory" is that it is merely a useful approximation which simplifies calculation at low frequencies. The Telegrapher's Equations which describe a TL at high frequencies are not "em field theory" (although they are closely related to Maxwell's Equations) - they are still derived from Kirchoff's Law, but by doing the "limit as x tends to 0" trick, the finite propagation problem is avoided by explicitly dealing with "where" and "when" which is what circuit theory does not do. One of the ironies of Catt's theories is that he uses the description of the TL in terms of impedance, characteristic velocity and "reflections" at impedance mismatches, which are an approximation derived from the Telegrapher's Equations, while while at the same time rejecting the Equations (and their method of derivation) because they predict a "high frequency cutoff" that the approximations (which ignore the implications of the TL's resistance) do not.

I am far from convinced that "energy current" is helpful. Catt's continually-recirculating "TEM wave" description of a capacitor is entirely due to "energy currents". His "energy current" is actually just the voltage/current product and is merely an obfuscation that conceals the fact that his version ends up with opposing currents flowing in the same conductor (which raises problems with Ohm's Law amongst other things), while the physicists' version has the current brought to a standstill. -- Kevin Brunt 06:36, 21 January 2006 (UTC)

Which to you seems the most likely?:

• a) the em waves coninue travelling (like Catt says) or
• b) the waves suddenly stop in zero time undergoing infinite deceleration (like the physicists say)

If you say b), what is the proposed mechanism for the stopping of these travelling waves? --Light current 19:58, 21 January 2006 (UTC)

Catt's waves not only have to decelerate, they have to accelerate in the opposite direction as well. If we're dealing with current flow in a conductor, the answer is c) the electrons continue to move at velocities determined by the temperature of the conductor, but the imbalance between the numbers moving with and against the direction of current flow ceases and the associated magnetic field 'evaporates'. The imbalance of charge due to the 'electron drift' however increases to a maximum, so the electric field increases. -- Kevin Brunt 23:13, 21 January 2006 (UTC)

Illustration of errors of Catt diagram: [3]. The Poynting-Heaviside vector is false if interpreted as saying that there is no propagation in the E and B vector directions. Forces act in the E and B field directions, and that means that energy is conveyed perpendicularly to the propagation vector c. The reality is that that the Poynting-Heaviside vector (Poynting and Heaviside discovered it independently) is holding back science. Quantum field theory of electrodynamics, which is verified for accurate predictions of (1) Lamb shift, (2) magnetic moment increase of electron due to vacuum and (3) magnetic moment increase of muon due to vacuum, says Coulomb's law is caused by the exchange of gauge bosons, which are photons. Coulomb's law is the force version of Gauss' electric field law, and so we know that photons are moving all the time along electric field lines. This is the cause of the force as specified by the quantum field theory (Feynman diagrams). So there is strong evidence the Poynting vector ignores the dynamics. (Quantum field theory is moving towards an ether picture of the Feynman path integral, due to problems with renormalisation in the purely abstract mathematical model. See arXiv: hep-th/0510040 [4] p85: the virtual particles in the vacuum contradict special relativity and imply a Dirac sea/aether as: 'it is not possible anymore to define a state which would be recognised as the vacuum by all observers'. There is evidence that 'string theory' is hogwash [5] as it makes no testable predictions, but its major rival is the 'spin foam vacuum' of loop quantum gravity, which again is a Dirac sea/aether.) 172.214.92.156 08:53, 21 January 2006 (UTC)

Reply to Kevin from LC

I agree that "circuit theory" is merely a useful approximation which simplifies calculation at low frequencies and that the Telegrapher's equations which describe a TL at high frequencies are not "em field theory" but are derived from Kirchoff's Laws. However here we must depart from theory to look at the experimental evidence. Anyone who has worked with square pulses on TLs will tell you that the description of the TL in terms of impedance, characteristic velocity and "reflections" at impedance mismatches are in fact correct.(as far as we can see). THe answer to your apparent paradox here is that you do not allow yourself the "limit as x tends to 0" trick where all components become distributed. When all component values tend to zero in the TL equations, the HF cutoff disappears! There is no inconsistency I feel in the way Catt has interpresed the experimental truths and the theories.

"Energy current" is helpful in thinking about these problems in that one no longer has to think about current and voltages on the wires (which probably do not exist at high frequencies anyway). Energy current will always give the correct answer. How do you think time domain reflectometry works if you dont believe in the Heaviside step of energy current?

Catt's "energy current" is actually the vector cross product of the electric and magnetic field (ie the Poynting vector that no one disputes)--Light current 19:12, 21 January 2006 (UTC)

No, the HF cutoff is real. The full derivation of the Telegrapher's Equations includes the resistance of the conductor and the leakage conductance of the dialectric, which leads to the extra terms that result in the frequency-dependent behaviour. And Catt is well-aware that a TL's resistance causes frequency-dependent results, because he has commented in detail on Heaviside's suggested inclusion of additional inductance to compensate for the problem in telegraph cables and the quarrel with Preece of the British Post Office on the subject.

I am not arguing against the description of a TL in terms of characteristic impedance, etc, because that is precisely what the Telegrapher's Equations predict! The problem lies in, for instance, Catt's pronouncement in chapter 6 of his "Electromagnetics" book where he concludes that the work that derives the Equations is wrong, and goes on to quote Davidson as say that, since a capacitor is a TL, modelling a TL as a capacitor is "absurd". In fact, the equations used by Catt, Davidson and Walton are derived from the modelling of the TL as a sequence of capacitors in the frst place, and the "absurd" gibe can be pointed straight back at Catt.

My objection to "energy current" is precisely that it hides voltage and current. Chapter 1 of Catt's Electromagnetics, while not specifically mentioning energy current, demonstrates the problem. Catt starts by showing that there is a magnetic field related to the charge moving in the inductance and an electric field related to the charge stored in the capacitance and that the energy held in each field is the same. He then treats the combined energy as a "wave" - effectively an "energy" current. He assumes that this wave is reflected off the open end of the TL and travels in the opposite direction.

In the case of a discrete pulse, at the moment the reflected leading edge passes the outbound trailing edge the pulse occupies a section of the line half of its original length, and with a voltage twice the original. Catt asserts that the energy is now flowing in both directions; that the magnetic fields cancel out (but the stroed energy doesn't), and that the two electric fields do not interact (or alternatively that the energy stored in a capacitor is not proportional to the square of the voltage!)

A little bit of thought reveals that the opposing magnetic fields that are cancelled out would be due to current (flow of charge) in opposing directions in the same conductor. A more orthodox analysis would require that the opposing currents cancel out completely, including the magnetic fields and that the correct view is that the reflected leading edge marks the point at which flow ceases. All the energy is stored in the capacitance. This view gets to the same numbers as Catt, and avoids several problems to do with the TL's resistance. -- Kevin Brunt 22:03, 21 January 2006 (UTC)

Actually, it was me - my sign-in timed out while I was thinking. -- Kevin Brunt 23:23, 21 January 2006 (UTC)

OK Kevin. But you see what I mean about signing - otherwise we don't know who the hell were talking to do we?--Light current 23:24, 21 January 2006 (UTC)

If the HF cutoff is real, at what frequency does it occur in real coax cables for example? --Light current 22:26, 21 January 2006 (UTC)

The full mathematics is beyond me. However, this is series R and shunt C, which is a "classic" low-pass configuration, so if you calculate 1/RC for a unit length of the cable you'll probably come up with a number that isn't that many orders of magnitude adrift.... -- Kevin Brunt 23:23, 21 January 2006 (UTC)

No you are wrong here. The only cutoff freq is when the cable goes into waveguide mode. This occurs at 20GHz for a 5mm dia cable with polyethylene dielectric. (ref Some questions and answers on fundamentals of coaxial cables - Tektronix UK Ltd c 1977) Losses are different and Im not talking about lossy cables. --Light current 23:58, 21 January 2006 (UTC) The explanation is the at the Ls counteract the Cs and the Cs counteract the Ls giving a purely resistive impedance that is not frequency dependent. (assuming L/C=R/G -- the so called lossless- or Heaviside condition) See Transmission line--Light current 00:41, 22 January 2006 (UTC)

But as you say, the "lossless condition" is a special case; in the general case there is a frequency-dependent component. Incidentally, I'm using the word "cutoff" because Catt does. I'm talking about an increasing attenuation, and related "phase" effects, with increasing frequency. -- Kevin Brunt 00:58, 22 January 2006 (UTC)

No, sorry. try another argument--Light current 00:59, 22 January 2006 (UTC)

It has dawned on me that Catt's "cutoff" may well be the limit above which the "smearing" of the edges of the pulse becomes so bad that the signal is lost. However, my real point is not so much the details of what is happening, but that Catt denies that there is something happening. I think that this is part of his "engineering versus science" mentality, which is probably behind his anti-academic pronouncements. In the half-century since he studied engineering at university there has been a great deal of change in the way that the relationship between "science" and "engineering"; in fact there has been a vast breaking-down of the distinctions between the different "subjects" altogether.

Catt seems not to have broadened his outlook. His writings portray him as having a very narrow view of everything from a 1950's engineering undergraduate point of view, with a vast disdain for the theoretical aspects. Anything that challenges his prejudices is not a opportunity to extend understanding, but is merely dismissed as irrelevant or obfuscation or just plain wrong. -- Kevin Brunt 20:39, 22 January 2006 (UTC)