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On Nov 13, 8:25*pm, Owen Duffy wrote:
If for example, the feedpoint Z of a 0.6 wave vertical over four quarter wave radials was 150-j500, your tapped coil matching network can be designed using bulk standard circuit theory to transform 150-j500 to 50 +j0, and nowhere do you use the missing 54° in those calcs. That's because the lumped-circuit model assumes that all signals travel instantly at faster than light speeds through the coil. At instant, faster than light speeds, the coil cannot possibly occupy any degrees of the antenna. When the real-world speed of light limit is taken into account by using the distributed network model, the degrees occupied by the coil falls out as part of those real-world calculations. The lumped-circuit model is simply flawed for the purpose of trying to determine the degrees occupied by the coil. I am finishing up an article on this subject. At 3.5 MHz, the velocity factor of the 100 turn, 10 inch long coil is 0.04, which makes the coil occupy 26.4 degrees when used for a 3.5 MHz mobile antenna. The "Axial Propagation Factor" from the Hamwaves Inductance Calculator at: http://hamwaves.com/antennas/inductance.html can be used to determine the number of degrees occupied by a loading coil. For the above coil at 3.5 MHz, the axial propagation factor is 1.8118 radians/meter. Multiplying by 1.4554 converts it to degrees/ inch. The coil is 10 inches long so: 1.8118(1.4554)(10) = 26.4 degrees occupied by that loading coil at 3.5 MHz. We can model a transmission line as lossless, but none exists in reality. We can model a loading coil that occupies zero degrees of the antenna, but none exists in reality. -- 73, Cecil, w5dxp.com |
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