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On Thu, 28 Aug 2003 12:18:44 -0500, W5DXP
wrote: Richard Clark wrote: So, Cecil (George, Peter, et alii), do you have an answer? Years ago, I had a discussion with Jeff, WA6AHL, here on this newsgroup. I suggested that the impedance looking back into the source might be Vsource/Isource, i.e. the transformed dynamic load line. However, I have never taken a strong stand on source impedance. If reflections are blocked from being incident upon the source, as they are in most Z0-matched systems, the source impedance doesn't matter since there exists nothing to reflect from the source impedance. My basic approach is to achieve a Z0-match and therefore forget about source impedance. Hi Cecil, That's all fine and well. It exhibits a rather standard behavior and confirms conventional expectations. I take by this response that you have no interest in the confirmation of interference in both Optical and RF metaphors being visited at the bench. That is fine too. It is a rather tough example to replicate - except when stumbled upon, then we hear cries for exorcism being needed (my cue). My missives simply offer touchstones of clarity in contrast to the murky sea of un-fettered statements. We are presented with fantastic notions that the characteristic source Z of a transmitter is unknowable, and this statement is usually closely allied to the notion that this same "unknowable" Z is actually responsible for reflecting all power arriving at the antenna terminal. Few of those who utter these witless jokes have any response to the straight line "So what is this Z that does all that reflecting?" In their chagrin, they fail even to repeat "it is unknowable...." Absolutely none can venture a guess that it is either: "much less than 50 Ohms," or it is "much more than 50 Ohms." This would be two obvious rejoinders and yet neither is uttered. Such is faith. The universal silence condemns their specious claims absolutely. These absurd notions deserve a hearty laugh, because it invalidates the need for a tuner which is purposely inserted between the source and load to serve that very purpose (and which you describe as your typical habit which is a nearly universal application). But, again, this discussion is generally reserved only for those interested in accuracy. :-) 73's Richard Clark, KB7QHC |
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