Home |
Search |
Today's Posts |
#11
![]() |
|||
|
|||
![]()
I have to agree with what Richard and some others have said.
First, that you've done a tremendous job of sharing your extensive knowledge and experience, and explaining transmission line phenomena in such a clear and understandable manner. We all owe you a great debt for this. But second, that there's something which you do state that I and some others can't accept. And that is that a "virtual" short (or open) circuit causes reflections, or that waves reflect from it. I maintain that for either to happen requires that traveling waves interact with each other. The "virtual" short or open is only the result of the sum -- superposition -- of traveling waves. Those traveling waves, and hence their sum, cannot cause a reflection of other waves, or alter those other waves in any way. Only a physical change in the (assumed linear) propagating medium can alter the fields in a traveling wave and cause a reflection. A real short circuit is in this category; a virtual short circuit is not. It doesn't matter if the waves are coherent or not, or even what their waveshapes are or whether or not they're periodic -- as long as the medium is linear, the waves cannot interact. You have clearly shown, and there is no doubt, that waves behave *just as though* a virtual short or open circuit were a real one, and this is certainly a valuable insight and very useful analysis tool, just like the "virtual ground" at the summing junction of an op amp. But I feel it's very important to separate analytical tools and concepts from physical reality. If we don't, we're led deeper and deeper into the virtual world. Sooner or later, we reach conclusions which are plainly wrong. There are many other examples of useful alternative ways of looking at things, for example differential and common mode currents in place of the reality of two individual currents, or replacing the actual exponentially depth-decaying RF current in a conductor with an imaginary one which is uniform down to the skin depth and zero below. But we have to always keep in mind that these are merely mathematical tools and that they don't really correspond to the physical reality. Unless I've incorrectly read what you've written, you're saying that you've proved that virtual shorts and opens reflect waves. But in every example you can present, it can be shown that all waves and reflections in the system can be explained solely by reflections from real impedance changes, and without considering or even noticing those points at which the waves superpose to become virtual short or open circuits. That, I believe, would disprove the conjecture that virtual shorts or opens cause reflections. Can you present any example which does require virtual shorts or opens to explain the wave behavior in either a transient or steady state condition? If I've misinterpreted what you've said, I share that misinterpretation with some of the others who have commented here. And if that's the case, I respectfully suggest that you review what you've written and see how it could be reworded to reduce the misunderstanding. Once again, we all owe you a great deal of thanks for all you've done. And personally, I owe you thanks for many other things, including setting such an example of courtesy, civility and professionalism here in this group (as well in everything else you touch). It's one I strive for, but continually fall far short of. Roy Lewallen, W7EL |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
Stub Matching software ? | Antenna | |||
Analyzing Woger | General | |||
Analyzing Woger | Policy | |||
A Subtle Detail of Reflection Coefficients (but important to know) | Antenna | |||
A Subtle Detail of Reflection Coefficients (but important to | Antenna |