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#1
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Cec wrote, "How does one amp at the top and zero amps at the bottom
grab you? Please see my other postings." It grabs me that what you wrote in your other postings about capacitance to the outside world, " I didn't say there was no capacitance to the outside world. I said such is a secondary effect, not a primary effect, and for the sake of the present argument, can be ignored as secondary effects often are ignored," is all wet. And I still say that your other postings before that were saying you believed that there was NO capacitance to the outside world. It was the message they sent to me, loud and clear. Given any volume, say a volume containing a Texas Bugcatcher coil and the air inside and immediately around it, if you push more electrons in than come out _for_ANY_abritrarily_short_time_period_, you have changed the net charge in that volume; if you pull out more electrons than go in, you have changed the net charge in that volume. If the current at the top and bottom, the only two conductors crossing the boundary of that volume, is different, that represents flow of charge into (and out of, in a cyclic fashion) that volume. I don't know what to call that except capacitance to the outside world. Yes, it's _distributed_ capacitance. But the key point is that it is THE reason--the WHOLE reason--for the difference in current between the top and the bottom, NOT a "secondary effect." In fact, when YOU say that the coil "behaves differently" in different external environments, you are AFFIRMING it as an important effect, for surely the presence or absence of some American gas guzzler (or is it Diesel guzzler?) strongly affects the capacitance to the outside world, and does not significantly affect internal capacitances (which in any event, being contained entirely within that volume, do NOTHING for storing net charge within the volume, because for those internal capacitances to store charge, what goes in one end comes immediately out the other end which is still inside the same volume and thus there is not any net change in charge within the volume). But the "other end" of capacitance to the gas guzzler or whatever is OUTSIDE the volume of the coil, thus EXACTLY accounting for the difference in current at the two leads going to the coil. -- I suppose they covered all that in a sophomore EE circuits class, but I wouldn't know. I suppose they also might have covered how a pure lumped model using only i(t)=C*dv(t)/dt and v(t)=L*di(t)/dt, with no time delay elements, can mimic lossless transmission line behaviour to any arbitrary degree of accuracy you want, but perhaps they don't try to hit you with that concept till later. I wouldn't know that, either...I just know it's true. I suppose it's a bit too much to ask all at once, but I do wish you could see that just because the specific value of the capacitance is different in different environments, it does not mean that I need a different model. The coil does not behave in some fundamentally different way. I only need to adjust the value of that capacitance within the model--or if you will, the parameters of the transmission-line-like behaviour, though other models may work as well in practical antenna analysis. The model stays the same; the parameters in the model change. When I change the value of a resistor, my model of a resistor doesn't change. It's still fundamentally v(t)=R*i(t). Only the value used for R changes. On a grander scale, when I include the parasitic effects of a real inductOR, I have more things to account for in the model than just inductANCE. Some of them are affected significantly by the environment in which I place the inductor. And even small changes in the values can have a profound effect on the overall system behaviour. That's especially true in a system operated near resonance where the Q is extremely high, such as a system in which there is only a standing wave. My only wish is that these musings will be useful to the lurkers trying to actually learn something, if there still happen to be any around. Cheers, Tom |
#2
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Tom, K7ITM wrote:
"Given any volume, say a volume containing a Texas Bugcatcher coil and the air inside and immediately around it, if you push more electrons in than come out_for_ANY_arbitrarily_short_time_period_, you have changed the net charge in that volume;---." No. This is not charging a capacitor or a battery. Energy stored in an antenna system is in constant motion. Power delivered by the transmitter is neadly the same as that used by the load, (the antenna), plus that consumed by losses. Power is simply the in-phase volts times amps. It can have any impedance which is the ratio of in-phase volts to amps. Z in the general case can include reactance plus resistance and can give the apparent power. It is the ratio of volts to amps without regard to phase. The coil which has a great difference between the current at its ends most likely simply has different impedances at its ends. The power is nearly the same at both ends of the coil but the voltage to current ratios are different. Varying impredance along the RF path is a product of the interference between the incident and reflected waves. A standing-wave antenna typically has an open-circuit at its end or ends. The RF has no other option but to be returned toward the sender and make standing waves. The large number of possible incident and reflected wave combinatioms makes it very likely that the current at opposite ends of a coil inserted in the antenna system will be unequal. It`s the power in and out of a coil in an antenna system that`s likely to be nearly equal at both ends. Best regards, Richard Harrison, KB5WZI |
#3
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Richard H wrote,
"Tom, K7ITM wrote: "Given any volume, say a volume containing a Texas Bugcatcher coil and the air inside and immediately around it, if you push more electrons in than come out_for_ANY_arbitrarily_short_time_period_, you have changed the net charge in that volume;---." No. ..." OK, I'm going to repeat it once mo If you shove more electrons into ANY volume than you remove, you have changed the charge within that volume. I do NOT care WHAT is in that volume. Current is the rate that charge is flowing past a point on a conductor. If the only way I have of getting charge into and out of a particular volume is through two wires, then the difference in current at every instant in time represents the time rate of change of charge within that volume. That is true INDEPENDENT of whether it is in an antenna, and it is INDEPENDENT of what's inside that volume. In fact, energy around an antenna is stored in electric and magnetic fields. These are inexorably linked to inductance along the conductors composing the antenna, and capacitance from these conductors to themselves and to any counterpoise or ground plane which may be part of the antenna--anything where electric field lines terminate. The charge per unit length along an antenna wire, be it resonant or not, be it a "standing wave" or a "travelling wave" antenna, varies with time. If it did not, then the current would necessarily be identical along the whole wire all the time. This all gets back to very basic definitions of charge, and current as the rate of flow of charge. It's all consistent with Maxwell, Gauss, Faraday, etc. and with waves both standing and travelling, and with "impredances" and all the rest. It's just amazing to me that some of you are fighting so hard against the very thing which has a chance of unifying your "wave" model with the realities of the electric and magnetic fields, and the associated capacitance and inductance along the antenna--indeed, along the wire itself, and not just along the coil. Without capacitance, there can be NO difference in current anywhere along the wire, because there is simply no place to put the charge implied by differing currents at differing locations. With capacitance and inductance, everything works just as it's supposed to--just as it DOES--and a properly developed wave theory will analyze it just fine, if that's your cup of tea. Cheers, Tom |
#4
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I don't understand what you are all on about, but, I side with K7ITM
"K7ITM" wrote in message Regards Mike. ups.com... Richard H wrote, "Tom, K7ITM wrote: "Given any volume, say a volume containing a Texas Bugcatcher coil and the air inside and immediately around it, if you push more electrons in than come out_for_ANY_arbitrarily_short_time_period_, you have changed the net charge in that volume;---." No. ..." OK, I'm going to repeat it once mo If you shove more electrons into ANY volume than you remove, you have changed the charge within that volume. I do NOT care WHAT is in that volume. Current is the rate that charge is flowing past a point on a conductor. If the only way I have of getting charge into and out of a particular volume is through two wires, then the difference in current at every instant in time represents the time rate of change of charge within that volume. That is true INDEPENDENT of whether it is in an antenna, and it is INDEPENDENT of what's inside that volume. In fact, energy around an antenna is stored in electric and magnetic fields. These are inexorably linked to inductance along the conductors composing the antenna, and capacitance from these conductors to themselves and to any counterpoise or ground plane which may be part of the antenna--anything where electric field lines terminate. The charge per unit length along an antenna wire, be it resonant or not, be it a "standing wave" or a "travelling wave" antenna, varies with time. If it did not, then the current would necessarily be identical along the whole wire all the time. This all gets back to very basic definitions of charge, and current as the rate of flow of charge. It's all consistent with Maxwell, Gauss, Faraday, etc. and with waves both standing and travelling, and with "impredances" and all the rest. It's just amazing to me that some of you are fighting so hard against the very thing which has a chance of unifying your "wave" model with the realities of the electric and magnetic fields, and the associated capacitance and inductance along the antenna--indeed, along the wire itself, and not just along the coil. Without capacitance, there can be NO difference in current anywhere along the wire, because there is simply no place to put the charge implied by differing currents at differing locations. With capacitance and inductance, everything works just as it's supposed to--just as it DOES--and a properly developed wave theory will analyze it just fine, if that's your cup of tea. Cheers, Tom |
#5
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Mike Coombes wrote:
I don't understand what you are all on about, but, I side with K7ITM "K7ITM" wrote in message Regards Mike. 1. If the magnitude of the forward current is the same at both ends of the coil, there is no net storage of charge. 2. If the magnitude of the reflected current is the same at both ends of the coil, there is no net storage of charge. These conditions satisfies K7ITM's requirements. But he is being fooled by the sum of the two above currents which is meaningless to net charge storage. Statements 1 and 2, above, already prove there is no net storage of charge. Looking at the standing wave current is meaningless after that technical fact. -- 73, Cecil http://www.qsl.net/w5dxp |
#6
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Cecil Moore wrote:
Mike Coombes wrote: I don't understand what you are all on about, but, I side with K7ITM "K7ITM" wrote in message Regards Mike. 1. If the magnitude of the forward current is the same at both ends of the coil, there is no net storage of charge. 2. If the magnitude of the reflected current is the same at both ends of the coil, there is no net storage of charge. These conditions satisfies K7ITM's requirements. But he is being fooled by the sum of the two above currents which is meaningless to net charge storage. Statements 1 and 2, above, already prove there is no net storage of charge. Looking at the standing wave current is meaningless after that technical fact. There is no "net" charge storage on a capacitor in an AC environment, either, Cecil, but you can still get current to go through it. I wouldn't argue with Tom too much if I were you, Cecil, because without the facts he's pointed out in regards to charge, your inchoate theorizing wouldn't mean anything at all. 73, Tom Donaly, KA6RUH |
#7
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Tom Donaly wrote:
There is no "net" charge storage on a capacitor in an AC environment, either, Cecil, but you can still get current to go through it. True, but completely irrelevant to the present discussion so more than likely another straw man. Once more, the subject is the RMS standing wave envelope reported by EZNEC. Brownian motion of individual electrons is completely irrelevant. -- 73, Cecil http://www.qsl.net/w5dxp |
#8
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K7ITM wrote:
If you shove more electrons into ANY volume than you remove, you have changed the charge within that volume. That is true but having zero standing wave amps at one end of a coil and one standing wave amp at the other end doesn't mean the charge is changing. If the forward current is the same magnitude at both ends of the coil, there's no change in charge. If the reflected current is the same magnitude at both ends of the coil there's no change in charge. The standing wave current is the sum of those two phasors. That sum is what is fooling you. Please pay attention to Hecht, in "Optics". The standing wave current profile does not move through the wire just as the standing wave light profile does not move through space. Standing wave current doesn't progress through a wire just as standing wave light doesn't progress through space. -- 73, Cecil http://www.qsl.net/w5dxp |
#9
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Hi there, Cec,
You wrote, "If the forward current is the same magnitude at both ends of the coil, there's no change in charge. If the reflected current is the same magnitude at both ends of the coil there's no change in charge." Dunno why you keep reverting back to magnitudes, but I'm talking about current as a function of time, and have been consistently through this whole thing. Until you get that straight, there's no point in your even taking part in this. "Cyclical variation in charge (contained within a volume)" means that on average the charge stays constant, but it does not mean that it's constant over some arbitratily short but finite length of time. Without the capacitance, without the ability to store charge, a transmission line, an antenna wire, a loading coil, all of them--would not have the ability to cause delay. Freespace, without a non-zero permittivity (capacitance), would allow infinite speed of light. But all these things DO have capacitance, and they DO have speed-of-propagation at the speed of light or slower. Cheers, Tom |
#10
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K7ITM wrote:
"Cyclical variation in charge (contained within a volume)" means that on average the charge stays constant, but it does not mean that it's constant over some arbitratily short but finite length of time. The current reported by EZNEC is RMS current, Tom. What happens within a cycle is irrelevant to this discussion. We are not and never have been discussing variations within a cycle. There's just no point. We have been discussing RMS values of currents. Your attempt to again divert the issue is noted. We are talking about net charge spread out over many steady-state cycles. That net charge is always zero no matter what the RMS value of the standing wave current at the ends of the coil. Without the capacitance, without the ability to store charge, a transmission line, an antenna wire, a loading coil, all of them--would not have the ability to cause delay. Freespace, without a non-zero permittivity (capacitance), would allow infinite speed of light. But all these things DO have capacitance, and they DO have speed-of-propagation at the speed of light or slower. Please tell us something we don't already know. It has become apparent that the discussion is not about coils at all. It is about the nature of standing waves whether existing in a transmission line, a standing wave antenna wire, or a coil. -- 73, Cecil http://www.qsl.net/w5dxp |
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