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#11
November 3rd 03, 08:31 AM
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Yes, I disagree with that.
Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: Of course it doesn't account for phase shifts of current, since there aren't any. You seem to be disagreeing with John Devoldere's "Bible" - "ON4UN's Low Band DXing", 3rd Edition, on page 9-34 at: http://www.k3bu.us/loadingcoils.htm A little thought should prove there is a current phase shift (delay) through the coil. Let's look at an 8 foot long center-loaded mobile antenna for 75m. The 4 feet below the coil gives a phase shift of about 5 degrees. Assume zero phase shift through the coil. The 4 feet above the coil gives a phase shift of another 5 degrees for a total of 10 degrees at the end reflection point. It's an open circuit, so a 180 degree phase shift takes place. That puts the reflected current at 190 degrees. Add the 10 degrees coming back and we see the reflected current arrives mostly out of phase with the forward current at the feedpoint. Since the feedpoint impedance is known to be around 15 ohms, these superposed currents cannot possibly be out of phase and must necessarily be in phase. The phase shift (delay) of the current simply cannot be the same with and without the coil. |
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