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Current through coils
Gene Fuller wrote:
I have no issue with the use of network theory, reflection coefficients, standing waves, or any other commonly used descriptions. However, none of these mathematical conveniences change the fundamental physical laws. If current, and therefore charge, appears to be unbalanced, then there must be charge storage somewhere. Gene, the flaw is in your misunderstanding of the fundamental physical laws, not in those laws. We measure the net current at one end of a coil at 0.1 amp and we measure net current at the other end of the coil at 0.7 amps (my web page example). The net current *APPEARS* to be unbalanced, but appearances can be deceiving. THERE IS NO STEADY-STATE CHARGE STORAGE ANYWHERE IN THE SYSTEM. Does this violate any fundamental physical laws? Of course not. Here's why (neglecting losses): V*I*cos(theta) equals the same power at both ends of the coil. That proves there is no steady-state energy storage. V1*(0.7)*cos(theta1) = V2*(0.1)*cos(theta2) This is a distributed network. A lumped circuit analysis fails miserably when you try to use it in a standing- wave environment and you have just proved it. That is also the same mistake that W8JI and W7EL have been making. The forward current at the 0.7 amp point is 0.4 amps at zero deg. The reflected current at the 0.7 amp point is 0.3 amps at zero degrees. The net current is the phasor sum of those two component currents. Inet = (0.4 amps at zero deg) + (0.3 amps at zero deg) Inet = 0.7 amps at zero deg The forward current at the 0.1 amp point is 0.4 amps at 82 degrees. The reflected current at the 0.1 amp point is 0.3 amps at -82 degrees. The coil causes an 82 degree phase shift in both forward and reflected currents and since their phasors are rotating in opposite directions, the sign of their phase shifts are opposite. The net current at this end of the coil is: Inet = Ifor + Iref Inet = (0.4 amp at 82 deg) + (0.3 amp at -82 deg) Inet = 0.057 amps + 0.043 amps = 0.1 amp at zero deg The fundamental physical laws are perfectly valid as has been demonstrated here. It is your understanding of them that seems to be the problem. You seem to have been fooled by appearances and as a result, you chose the wrong model with which to try to solve the problem. The distributed network analysis was developed because the lumped circuit analysis falls apart under certain circumstances. One of those circumstances is the presence of standing waves like the ones that exist in a 75m mobile antenna. -- 73, Cecil http://www.qsl.net/w5dxp |
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