The Dark Side of the Conjugate Match

Discussion in 'General Technical Questions and Answers' started by KL7AJ, Mar 12, 2010.

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  1. W5DXP

    W5DXP Ham Member QRZ Page

    Tom, your insistence that current travels through a one foot long 75m loading coil, with a VF of 0.03, in 3 ns is based on the belief that RF energy can travel faster than the speed of light. Walt's insistence that a source can shift its load-line without reflected phasors being incident upon the source is based on the belief that RF energy can travel faster than the speed of light. Faster than light speeds are required by the lumped-circuit model with which we all have been brainwashed from an early age. Why don't we all just agree that nothing can travel faster than the speed of light?
     
  2. W4PG

    W4PG Super Moderator Lifetime Member 279 Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Please keep the comments respectful of others. Agree to disagree if necessary but don't personally attack others. Some of you are close to needing a time out.

    .............Bob
     
  3. W5DXP

    W5DXP Ham Member QRZ Page

    Walt, how does the reflected energy get reflected at the source if it is never incident upon the source? That sounds like a catch-22 to me. Exactly what is your definition of "reach"? I have been using "reach" as a synonym for "incident upon".

    For instance, I would say that some of the energy is reflected from a mismatched load when the forward energy reaches the load, i.e. gets to the load, i.e. is incident upon the load.

    I have been arguing that the source load-line cannot change unless reflected energy is incident upon the source. Please don't tell me that we have been arguing over the definition of the word, "reach". When I reach Houston, I can stop at the city limits and never enter Houston.
     
    Last edited: Sep 23, 2010
  4. W5DXP

    W5DXP Ham Member QRZ Page

    Sorry, I'm probably the offender - too much wine in the afternoon coupled with a sense of humor akin to Don Rickles, e.g. “Who picks your clothes - Stevie Wonder?” :) My apologies if I have offended anyone.
     
    Last edited: Sep 23, 2010
  5. W5DXP

    W5DXP Ham Member QRZ Page

    Because the disagreement is almost never over technical facts. After all, a fact is a fact. If we agree on technical facts, then what is the argument all about? It is good to get an answer to that question and it is almost always a semantic problem, a misunderstanding that can indeed be resolved assuming that we don't simply "agree to disagree" and leave a festering problem cowardly unresolved.
     
  6. G3TXQ

    G3TXQ Ham Member QRZ Page

    Cecil,

    I've been quietly following the debate :)

    I have this question based on what I believe you are saying:

    Let's take a typical solid-state PA module comprising a single-ended pre-driver stage, followed by a push-pull driver stage, and then a push-pull final stage. If the PA is connected through a TL to a load which undergoes a step change in value, it seems obvious that the push-pull final will not "see" that change until the reflected wave arrives back at the source.

    But here's my problem: where, exactly is the source?

    The step change in the load-line of that final stage will cause a change to its input impedance, and that will appear as a step change in the load-line of the driver stage; in turn that will cause a change to the load-line of the pre-driver stage. and so on. The effects will diminish as we move back along the stages, but they are there nonetheless.

    Are you claiming that the reflected wave "reaches" back into the Tx through all stages in the chain? If not, what "communicates" the change to those earlier stages, according to your model?

    I'm not sure if your model requires us to view all activity within the Tx in terms of wave mechanics!

    73,
    Steve G3TXQ
     
  7. W8JI

    W8JI Ham Member QRZ Page

    Cecil,

    The reason I do not engage any topic with you is you tend to re-write and intentionally misquote what other people say. This makes it impossible to have civil technical discussion.

    I never said or implied, and Roy Lewallen never said or implied, anything travels faster than light. Walt has not said that, and no one else I'm aware of has said that.

    Please stop publically inventing statements and attributing them to others.

    73 Tom
     
  8. W5DXP

    W5DXP Ham Member QRZ Page

    Tom, Because the loading coil discussion is off topic for this thread, I'm starting a new thread titled: Delay through a loading coil, which will begin with a quote of your above posting.

    In that thread, I will prove that you have implied that current travels faster than the speed of light through your 100 turn, 2" dia, 10" long, 75m loading coil.
     
  9. W5DXP

    W5DXP Ham Member QRZ Page

    Walt, that E/I ratio is equal to (Vfor+Vref)/(Ifor+Iref), bolded to indicate phasors/phasor-math. If the reflected waves do not see a physical short, open, or pure reactance at the tuner output, not all of the reflected energy will be re-reflected. We are going to have to agree to disagree on that point and probably cannot proceed with this discussion because of the impasse. The question is: How does an E/I ratio cause a reflection at one point but not at another point?

    In a matched system, it can be proved that some of the reflected energy makes it to the tuner input capacitor where it is re-reflected at the 50 ohm Z0-match. You are correct that there is a reflection at the impedance discontinuity caused by the capacitor on the output of a network (tuner) but it is only a partial reflection. There is another reflection caused by the coil and yet another reflection caused by the capacitor on the input of the network. The 50 ohm Z0-match which eliminates reflections in a matched system is at the input capacitor, not at the output capacitor. Here's a diagram of a network (tuner) in a matched system:

    no reflections--input--a--Cap--b--Coil--c--Cap--d--output---reflections

    It can be shown that reflections exist at points b, c, and d, but not at point a. If it helps, put a one-wavelength piece of lossless transmission line between the tuner components and see what happens.

    If that 50 ohm Z0-match doesn't exist, as it doesn't in a mismatched system, reflected energy proceeds to become incident upon the source. If the source load-line changes during a mismatch, reflected energy is incident upon the source because, in the real world, there is nothing else that can cause a change in the source load-line, (assuming that the final amp is not readjusted). Here's a diagram of a network (tuner in a mismatched system).

    reflections--input--a--Cap--b--Coil--c--Cap--d--output---reflections

    A simple Bird directional wattmeter reading will show reflections at point a. Reflections exist at every point in the mismatched network. If the source load-line shifts away from the matched case, then in the real world, reflected energy has to be incident upon the source.

    There is no proof that an E/I ratio, by itself, is sufficient to cause a reflection, e.g. there are E/I ratios all up and down a transmission line that do not cause reflections. There is lots of proof that it takes a physical impedance discontinuity to cause a reflection and unless that physical impedance discontinuity is a physical open, short, or pure reactance, only partial reflections are possible. When all of the reflected energy reverses direction at an impedance discontinuity that is not a physical short, open, or pure reactance, wave cancellation between two complimentary waves is involved as well as re-reflection of the single reflected wave.
     
  10. W8JI

    W8JI Ham Member QRZ Page

    It's best to let it go Walt.
     
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