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Cecil Moore wrote:
Gene Fuller wrote: I thought you denounced and denied this "concept" earlier today. Guess you misunderstood. A coil can replace 30 degrees of an antenna but it won't use the same amount of wire as 30 degrees of wire. What I said is that an inductor is more efficient than linear loading. Cecil, I am feeling dizzy. I am quite comfortable with my understanding of the entire problem, but I am seriously confused about your position. Nobody has ever talked about efficiency or the length of wire needed. The issue has always been replacing "degrees of antenna". I have captured a few excerpts from April 7. 73, Gene W4SZ Excerpt follow: 9:03 am -- From Cecil K7ITM wrote: Another 'speriment occured to me, for those who think the coil current MUST be different at the two ends by the amount corresponding to the antenna section it replaces: To the best of my knowledge, nobody believes that. The coil is much more efficient at the loading function than is the straight wire from which it is made. That's why inductive loading is more efficient than fractal antennas or other types of linear loading. -- 73, Cecil http://www.qsl.net/w5dxp 9:24 am -- From Yuri [excerpt] Now you move that coil say half way up the must, to higher impedance point at the antenna, and that coil now, in order to maintain the "match" has to have higher impedance, more turns and will exhibit MORE current drop across it, while replacing THE SAME NUMBER OF "missing" DEGREES AT THE RADIATOR. Assuming that our goal is to stay with the same physical length of the whip (which we do) and maintaining 90 degrees of resonant radiator. So the radiator stays 50 degrees ()+50, 10+40, 20+30, 30+20, 40 + 10) long and coil replaces the same "missing" 40 degrees. [emphasis was in the original message] 9:44 am -- From Cecil Roy Lewallen wrote: Of course loading coils can be expressed in electrical degrees. But extrapolating this to mean that a loading coil has the same properties as an antenna with the same number of "degrees" has no justification. I haven't heard anybody make that assertion in years. Coils occupy whatever number of degrees that they occupy. 8:49 pm -- From Cecil [excerpt] Example: The phase shift from 30% to 60% in the traveling wave antenna is taken from the tabular data as 54.2-27.6 = 26.6 degrees. The phase information is in the *phase* in a traveling wave. For the standing wave current, the situation is completely different. The phase measured between any two current probes will always be zero. The phase of a standing wave current is useless for measuring phase shift. The way to extract the phase information is to measure the *amplitude* at two points and then calculate the phase shift by taking the arc-cos of the normalized amplitude. Example: The phase shift from 30% to 60% in the standing wave antenna is arc-cos(0.8843) - arc-cos(0.5840) = 26.5 degrees. The phase information is in the *amplitude* in a standing wave. Thus in both antennas, the phase shift in 30 percent of the wire is about 27 degrees. (90*.3 = 27) If we had a coil installed in that 30 degrees of the antenna instead of a wire, the same concepts would apply. |
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