*From*: Vinu Arumugham <vinu@xxxxxxxxx>*To*: olaney@xxxxxxxx*Date*: Wed, 01 Aug 2007 10:45:01 -0700

Orin, Since the reflected and propagated waves have identical properties and are indistinguishable, how can you be sure it is one and not the other? Thanks, Vinu olaney@xxxxxxxx wrote: > Vinu: > Steve is correct. We all agree that the single special case of > identical waves (or some fraction of both waves that can be said to be > that way) approaching from both directions looks and acts in a way > that can be interpreted as if there was wave collision. We all agree > on that, so why belabor it? However, the collision theory supposes > that somehow the physics is different just for this special case. If > you acknowledge that non-identical signals pass through each other, > then why not accept the exact and correct results if you assume that > everything, different or identical, passes through without > interaction? Why bother with a special case at all? It's a needless > complication. > > Furthermore, the fundamental physics does not support a collision > model. Here's a quote: > > "As discussed in Lesson 2 > <http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/newtlaws/u2l2a.html#top>, > some forces result from /contact interactions/ (normal, frictional, > tensional, and applied forces are examples of contact forces) and > other forces are the result of action-at-a-distance interactions > (gravitational, electrical, and magnetic forces)." > http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/newtlaws/u2l4a.html > > Applying a contact model to an action-at-a-distance interaction is a > conceptual error. Gravity does not rebound as the planets pass each > other, and broadcast waves slip through each other effortlessly. The > sea of electrons in metal supports electrical waves that do the same. > > Orin > > On Tue, 31 Jul 2007 15:20:23 -0700 Vinu Arumugham <vinu@xxxxxxxxx > <mailto:vinu@xxxxxxxxx>> writes: > > Here is some ASCII art with "colored" waves. The LLL and RRR > > represent > > portions of a T-line charged by a wavefront. <,> represent > > wavefronts > > traveling in indicated direction. > > Assume 50 ohm lines, 20mA current changes resulting in 1V > > wavefronts. > > > > Incident waves of equal magnitude: > > LLLLLLLLLLLL> <RRRRRRRRRRR > > > > Reflection model : > > <LLLLLLLLLLLRRRRRRRRRR> > > LLLLLLLLLLLLRRRRRRRRRRR > > > > Wave propagation model: > > <LLLLLLLLLLLRRRRRRRRRR> > > RRRRRRRRRRRLLLLLLLLLLLL > > > > Unequal incident waves, left is 2V, 40mA, right is 20mA, 1V: > > LLLLLLLLLLLL> > > LLLLLLLLLLLL> <RRRRRRRRRRR > > > > Reflection model: > > <LLLLLLLLLLLLLLLLLLLLLL> > > LLLLLLLLLLLLRRRRRRRRRR> > > LLLLLLLLLLLLRRRRRRRRRRR > > > > For the unequal wave reflection model above, at the point where the > > wavefronts meet, no charge can flow (I=0) from the right wavefront > > to > > the left T-line because the lines are charged to the same potential. > > I=0 > > means the right wavefront sees an open circuit and reflects. When > > this > > point reaches 2V, the 40mA left incident wavefront can charge both > > the > > T-lines with 20mA each, sending a 1V wavefront into the right > > T-line, > > and a 1V reflected wavefront going back on the left T-line. So the > > left > > incident wavefront can be described as having encountered a high > > impedance (>50 ohm and <open circuit) whereby a 2V incident wave > > produced a 1V reflected wave. > > > > Wave propagation model: > > <RRRRRRRRRRLLLLLLLLLLL> > > LLLLLLLLLLLLLLLLLLLLLLL> > > LLLLLLLLLLLLRRRRRRRRRRR > > > > Thanks, > > Vinu > > > > > > steve weir wrote: > > > Ihsan, I've presented two methods that both correctly predict the > > > results: One based on modeling the intersection as an open to the > > > > > even mode, while short to the odd mode, and the other on what I > > think > > > is far simpler: continuous propagation of each of the original > > wave > > > fronts. Use whichever model makes your day simpler, but for my > > money > > > I'll stick with the latter. I prefer the view that > > discontinuities > > > and resulting reflections in quasi uniform, infinite length, ie > > > terminated transmissions are the result of physical variations in > > the > > > channel, not patterns of energy I happen to launch into them. > > > > > > Consider for example +1.0V step from the left, and a +0.5V step > > from > > > the right. After they meet, the voltage moving rightward > > continues to > > > rise by +1.0V from its previous value, and the voltage moving > > leftward > > > continues to rise by +0.5V from its previous value. The waves > > just > > > linearly superimpose. > > > > > > Regards, > > > > > > > > > Steve. > > > > > > > > > Ihsan Erdin wrote: > > >> Steve, > > >> > > >> The wave propagation is simply the transfer of the energy in > > space. > > >> For the special case a line symmetrically driven at both ends, > > one can > > >> use the model of an unterminated transmission line driven from > > one > > >> side only and no one can tell the difference. This is based on > > the > > >> fundamental electromagnetic principle: image theory. > > >> > > >> For the uneven drivers of your example, I can rightfully argue > > that > > >> the equal frequency components "bounced" and cancelled out while > > the > > >> residual part kept on propagating. The idea of waves passing > > through > > >> each other is simply a matter of perception; not a rocksolid > > physical > > >> reality which ridicules the idea of waves bouncing in the middle. > > Both > > >> cases have equal footing and at the end it all boils down to the > > >> choice of modeling. > > >> > > >> The billiard ball example was an interesting attempt but not > > quite > > >> equivalent. At the collision the balls will have to come to a > > >> momentary full stop before accelerating in the reverse direction. > > This > > >> is not symmetrical to the case where they (might) pass through > > each > > >> other at constant speed. > > >> > > >> Best regards, > > >> > > >> Ihsan ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu

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