em

The nature of space

Ivor Catt. 5th March 2010.

Comment on "Crosstalk (Noise) in Digital Systems"

In 1980 I wrote;

Space is the ability to accommodate energy.

The first thing is that energy (current) can enter a region of space if its aspect ratio is acceptable – 377. That is, the ratio between the electric dimension and the magnetic dimension of the energy needs to be 377. If the region contains a dielectric with permeability of permittivity which is different from that of vacuum, the energy current has to have a different aspect ratio in order to enter it. If the aspect ratio is wrong, then some of the energy current will reflect at the entry point to that region of space.

We know something about the collision of two energy currents at 180 degrees. Superposition applies, except that while they overlap, there is a brief lateral force between the guiding conductors. This is discussed starting at page 258 and 260 of my book .

At page 13 of my other book , there is discussion of what happens if two pulses collide at a four way junction. If they are of the same polarity – called “dissimilar pulses”, they help each other across the gap. If they are of opposite polarity, “similar pulses”, they are deflected through 90 degrees.

The advance I made today relates to what I have found out from my 1967 paper

"Crosstalk (Noise) in Digital Systems" , pub. IEEE Trans. Comput., vol. EC-16, no. 16, December 1967, pages 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 31 , some of which is in two of my books. The argument starts at page 30 of one book , and at page 4 of the other book , continuing on page 55 . Here in figure 9.2 we see “a very narrow pulse introduced at the front end of the active line. If there were no parallel passive line nearby, this pulse would travel down the active line (at the speed of light for the dielectric) more or less unchanged,” in a TEM mode. “However, as the other two traces show, the presence of the passive line caused the original narrow pulse to break up into two similar pulses.” In figure 9.3 we see that the two pulses are of opposite polarity on the passive line, and initially were superposed. Thus, two energy currents of opposite polarity were travelling together in the same direction at the same point, close to the passive line. Had there been uniform dielectric throughout, with conductors buried between voltage planes, these two opposite energy currents in the vicinity of the passive line would continue to travel together. This leads to my new insight gained today, which is that a region of space can accommodate two energy currents of opposite polarity at the same point in space.

If we attach a 500 ohm oscilloscope probe to the inner and outer of a coaxial cable, it has a series 450 ohms at the probe point followed by a 50 ohm coaxial cable terminated by 50 ohms at the other, oscilloscope end. If a 10 volt pulse travels from left to right down the coax cable, a 1 volt pulse will travel up the probe cable to the oscilloscope, where it will be represented as 10 volts. Now if the 10 volt pulse came from the right, an identical 1 volt pulse will be picked off and travel to the oscilloscope. At the probe point, information as to the direction of the 10 volt pulse is lost. If two pulses, one from the left and one from the right, overlap, the oscilloscope will receive a 2 volt pulse, and register 20 volts. If however one of the two pulses had opposite polarity, the oscilloscope will register zero volts.

Neither the 20 volts nor the zero volts represent the real situation at the probe point. The reality is that at that point, one 10 volt signal is travelling to the right, and another to the left. The oscilloscope’s 20 volts or zero volts are creations of the probing system, which neglects direction. The reality is that when the two pulses overlap, they remain two 10 volt pulses, and should not, and cannot, be mixed together. There is no 20 volts and there is no zero volts.

After centuries of brainwashing we are trained to think that there exists a single potential difference between the inner and outer of a coaxial cable. The truth is that there are two voltages, one associated with a TEM wave travelling to the right, and a totally independent one associated with a TEM signal travelling to the left. Also, they have a magnetic field just as much as they have an electric field. We ignore the magnetic field value because it is much more difficult to measure, but this should not have been allowed to make us neglect it.

Ivor Catt March 2010