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Roger wrote:
As your argument is developed below, you begin using positive x. What is the zero point it is referenced to? I will assume that it is leading edge of original reference wave. Not speaking for Roy, but x is usually 0 at the feedpoint of a 1/2WL dipole, for instance. For any fixed time t=N, the phase of the standing-wave signal is constant all up and down the antenna. Please ask Roy how that fixed phase can possibly be used to measure the phase shift through a 75m bugcatcher loading coil. Wow! This would happen if the re-reflection actually reverses. How could this occur if we consider that voltage is a collection of positive or negative particles? We would have a positive reflection meeting with a positive outgoing wave (or negative meeting negative). The situation would be the same as at the open circuit end immediately following initial reversal, or current would simply stop flowing from the source. RF engineering convention in phasor notation: If the wave reflects from an open circuit, the current reverses phase by 180 degrees such that If+Ir=0. The voltage does not reverse phase so Vf+Vr=2Vf=2Vr. If the wave reflects from a short circuit, the voltage reverses phase by 180 degrees such that Vf+Vr=0. The current does not reverse phase so If+Ir=2If=2Ir. Incidentally, this is a different convention from the field of optics. I think you would agree that a steady state standing wave would form immediately upon reflected wave reaching the initiating source if the wave did not reverse. This is a tricky subject covered by many discussions among experts. My take is that since the impedance "seen" by the reflections is usually unknown (possibly even unknowable) the discussion is a moot point. The convention is that if reflected energy enters the source, it was, by definition, never generated in the first place. All that is important at the output of a source is the *NET* power output. Energy flow back into the source is, by definition, completely ignored. The gif's certainly made it clear why you are skeptical of the power of traveling wave analysis. The Poynting vector yields the power density of any EM traveling wave. The power density equations from the field of optics are just as valid for RF waves as they are for light waves. If one wants to understand the redistribution of energy, one will need to understand constructive and destructive interference during superposition. Roy is on record as not caring where the energy goes. -- 73, Cecil http://www.w5dxp.com |
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