Questions for Classical Electrodynamics.


Footnote to Questions for Classical Electrodynamics.

Ivor Catt. 22 March 2010





Today, 22 March 2010, John Dore tells me that USB has been using bidirectional signalling down one twisted pair for some years. This means that the section below, which I added to yesterday, means that I was waiting for something to happen which had already happened. But see next day.

Ivor Catt



I should mention that over the decades I have spent enormous time on Heaviside, and my interpretation of his “duplex telegraphy” was not to send signals in two directions down the same wire(s), as John Hunt seems to say. I thought that the idea originated with me in the context of today’s computers for the interconnections between computer and printer, for instance. Until today I kept it secret. I do hope my co-author Mike Gibson, who is the top expert in the world on Heaviside’s writings, will clarify this.


It is quite extraordinary that today ‘Duplex Telegraphy’ has been forgotten. There is a crying need for two way signalling using the same conductors between modules, for instance computer and printer, in today’s computers. I have watched with amazement the failure of the industry or the profession to move to two way signalling. For me, the ideal is to have only two conductors between a pair of modules, signal and ground, and work the line with high speed serial. This gives major cost advantages, and makes failure modes easier to detect because catastrophic. However, at least, after a delay of a decade or two, the industry has moved from ghastly fully parallel to serial intercommunication. John Foggitt will confirm that I was arguing for serial more than a decade before the industry moved from parallel to serial. I have kept quiet about what Heaviside called “duplex” signalling, and waited to see if the industry would realise that that is the proper way for inter-module intercommunication. This is the first time, 22 March 2010, that I have mentioned it anywhere. It is easy to do. The key is to use the ECL circuit.