Okay, I think this is what I'm trying to say. Say you have one co-ax cable. You turn on the generator, and the wave begins to propagate down the cable.
this *is* time transient As the wavefront moves, the capacitance along the cable gets charged little by little. Imagine a bajillion capacitors in parallel along the cable.
right on If there is no resistance, they each get charged up as the wave propagates across them. If there is resistance, the rate at which all the little caps get charged isn't dependent only on the speed of the wave.
well, ok. But don't confuse this resistance to Ohmic resistance. This increased in charge time would be due to the dielectric constant slowing the propagation of the wave... which I think is what you are saying. So now as you charge the caps further and further down the line, your current decreases
haha, you are right, but I wonder if for the wrong reason? The instaneous current at any particular location will be less because the wave is spreading out. This is known as dispersion & can only occur with lossy line. and so does the rate of charge.
THAT is effect of the dielectric constant In fact, the rate of charge may not even keep up with the speed that the wave propagates
oops! That is where your analogy just fell apart. The sequence of Ls & Cs is the model of the tx line. The wave ... is *the* wave which is what is doing all of the charging.and you may end up charging several caps in parallel rather than just the one nearest the wavefront. As the length over which the wave occupies increases, so does the resistance.
the resistance doesn't change ... in any of your usages ... assuming a uniform tx line So as the wave moves across the line, your overall current is dropping. This causes a change in the circular H-field. Would this not cause transmission all over the place?
This would be true if the wave could get ahead of itself. haha I'll throw another term at you, "causal" or causality. Which simply defined means that the coax line cannot anticipate what is coming down the tube.
I realize this is not reflection, but my real question was actually the mechanism which alters the field such that it reflects the current
a reflection is only due to a change in impedance be it the end of the tx line is not perfectly terminated or along the line due to defect or intent that should be in the line. I thought some kind of reflection was the source of the field correction. Cuz ultimately, I should be able to apply ampere's law around the cable and find the current.
you can on the forward wave and include the reflected wave ... if it exists But with there being no reflection, it almost didn't seem like the field was changing. I don't even want to think about the transient behavior of the field in the conductor itself
that statement is why my 1st comment was that this is transient behavior