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jimg wrote:
EZNEC4 computes the antenna currents. Knowing the voltages would be interesting. Unlike the feeder line where the voltage or current are easily determined from the characteristic impedance, the line parameters, and the terminating impedance, how do you determine the antenna voltages? You don't. Voltage is a measure of the potential between two points. When those points are separated in space and in the presence of a changing magnetic field, which is the situation near an antenna, the voltage you would measure depends on the path you take between the two points. Crudely and not completely accurately put, it depends on how you orient your meter leads. First blush says, uh, 377ohms relates the voltages and current, but that's in free space. No. 377 ohms is the ratio of E to H field of a plane wave in free space. It isn't the ratio of any voltage to any current anywhere. There is no current in free space, and voltage depends on the path you take, as I said above. The antenna has radiation, inductive, and electric fields (well, the radiation field is actually the transverse electric field component), so how does one go about getting the voltage as a function of antenna position (EZNEC current). You don't. It's not possible. Which is why EZNEC doesn't do it. I'm sure the answer is obvious but I'd appreciate confirmation (of an answer and my clouded intellect). Thanks. Roy Lewallen, W7EL |
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