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Ian White GM3SEK wrote:
Be very careful here. We're talking about the effect of cutting the physically shortened wire antenna, and inserting a loading device. This therefore has to be a TWO-terminal device. Yes, I realize that. Do you realize that the characteristic impedance of a single #14 wire 30 feet above ground is 600 ohms? That pesky ground return path raises its ugly head once again. It's impossible to install a two-terminal system 30 feet above *ground* and have it remain a two-terminal system. It's only a two-terminal system in your mind. Electrical current is defined as a net rate of transfer of electrons, so by the very definition of the term there is literally no such thing as a non-flowing current (except when the current is exactly zero and the definition becomes moot). You have hit the nail squarely on the head without realizing it. A non-flowing current doesn't exist in reality but that is exactly what you are measuring when you measure standing-wave current. The only things that exist in reality are the forward and reflected current. So you guys are basing your high and mighty concepts on something that doesn't even exist in reality. No wonder you are confused. You are measuring two currents flowing in opposite directions at the same time and don't realize it. I seriously wonder if you understand what a standing wave is. It is simply a pattern of variation in current along the length of a transmission line, which is stable in time. Nope, that's not what it is. For example, a current standing wave on a particular transmission line is the sum of one amp flowing in one direction and one amp flowing in the opposite direction. Exactly what is the net charge flow when identical currents are flowing in opposite directions? Let's see now, this is a really tough one. One amp flowing in one direction minus one amp flowing in the opposite direction. What could the result possibly be? :-) Hint: think DC to see what the net charge flow would be. If you pick any point along the transmission line or antenna wire, there is a simple net current characterized by one amplitude and one phase, relative to some other reference point. (In this whole discussion we discount the normal cyclic sinusoidal variation of instantaneous RF current which is happening everywhere in the system.) I suggest you review traveling wave phasors which rotate at omega (2*pi*f). A standing wave 'phasor' doesn't rotate at all so a standing wave current is not moving. I'm not even sure it is technically valid to call a standing wave current a "phasor" since it doesn't even possess a frequency characteristic. Please think about a perfectly stationary, non-revolving 'phasor' and then comment. Wouldn't a non-revolving phasor be DC? To be valid, your concept must do nothing more than explain what's seen to be happening; it cannot seek to affect it. The same thing applies to your concepts. So what do your concepts say about a phasor with an omega(2*pi*f) equal to zero as is the case for standing waves? Are standing waves really DC? Do they exist at all anywhere besides the human mind? At the point where you have to say that a measured (and therefore measurable) current does not flow, your concept is in trouble. Sorry, I have absolutely no idea what that means. Surely you have measured zero current at a standing wave current minimum where the forward current equals one amp and the reflected current equals one amp. Is that zero amps in the act of flowing? Your length of coiled up coax is a FOUR-terminal device, like Richard's transformer was. It isn't an applicable solution for this problem. If you include that pesky ground under antennas, it is. My electronics equation book contains a formula for the characteristic impedance of a single wire transmission line over ground. Is that invalid? Doesn't that sound very much like a dipole wire in the air? The laws it violates are those of logic. Your black box is not allowed to sometimes have two terminals and sometimes need four. An antenna system installed on this earth is always a four terminal system whether you like it or not. Haven't you ever seen those diagrams of the current return to ground from an antenna system? -- 73, Cecil http://www.qsl.net/w5dxp |
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