27 October 2011
In his letter in the September 2011 issue of EW Ivor Catt flatly rejects the concept that current can flow in two directions along the same conductor. He writes: ‘I say that the idea that electrons can hop along down a conductor in both directions, waving to each other as they pass, is truly amazing.’ He appears to believe that electrons are the only entities capable of moving electric charge from one location to another.
As far as I am aware, Ivor has never mentioned the existence of photons in any of his articles. The Wikipedia definition of this entity is ‘In physics, a photon is an elementary particle, the quantum of electromagnetic interaction and the base unit of light and all other forms of electromagnetic radiation’.
Since photons can travel through solid material (glass), there should be no problem in accepting the fact that they can also travel along conducting material. Light can be reflected back towards its source. So can current. The relationship between photons and electrons in a conductor can be likened to that between the wind and waves on the sea.
The concept of incident and reflected current at terminations is an essential feature of the analysis of radio frequency circuits and of transients in transmission lines. It is not too difficult to visualise two streams of photons propagating in opposite directions along a conductor. Each stream can be treated as a partial current. The total current at any cross-section is the sum of the two.
Conventional transmission line theory is an analysis of the behaviour of differential-mode currents and voltages. It is possible to visualise the propagation of energy either as a movement of charge along a conductor or as an electromagnetic wave in the immediate environment. Since this analysis assumes that the current in the ‘return’ conductor is equal in magnitude but opposite in direction to that in the ‘send’ conductor, it effectively ignores the existence of the antenna-mode current. That is, conventional books on transmission-line theory ignore the existence of interference.
If it is accepted that antenna-mode current exists, then it must also be treated as a partial current.
If it is possible for two partial currents to propagate in opposite directions along a conductor, then it must also be possible for two currents to propagate in the same direction along a conductor at different velocities. This is what Ivor observed in his experiment; the one reported in the January 2011 issue of E.W. It is an interesting experiment, one which could be carried out by any reader with access to the right equipment.
The fact that this phenomenon is not described in standard textbooks does not mean it does not exist. It just means that the authors of such textbooks merely regurgitate material from previous textbooks.
Nor is it valid to conclude that it is necessary to develop a completely new theory of electromagnetics, as Ivor suggests. Existing theory is perfectly capable of explaining the phenomenon.
Ian Darney
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