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Magnetic Loops
"J.B. Wood" wrote in message ... Hello, and that seems to be ham radio jargon. Hams seem to think the adjectives "magnetic" and "electric" are needed when referring to loop and dipole antennas, respectively. Textbooks on electromagnetics and antennas don't use those terms except in the case when discussing theoretically small radiators, i.e. "magnetic dipoles" and "electric dipoles". My hypothesis on the ham terminology is that a loop is viewed as an inductor. That's OK for close-in (non-radiative) mutual coupling to some source but when you're several wavelengths away (in the far field) then the loop (or dipole antenna for that matter) responds to the electromagnetic field (the electric and magnetic far fields can't be considered separately). The fact that an axis of either antenna lines up with the electric or magnetic field vector in the far field is moot. Does this mean that the loop doesn't have inductance? Of course not and it plays a role in establishing the feedpoint impedance of the loop at the operating frequency. Now if folks would just stop using that word "literally" so damn much... Sincerely, and 73s from N4GG0, Hi I totally agree with you. You only get a feeling of an antenna behaviour a few wavelength from it. This is very hard to do at HF for amateurs. Specially in the vertical plane. I made a few tests of small loops in the broadcast FM band. What surprised me was their ,almost perfect,omnidirectional behaviour in horizontal polarisation. A too small vertical dipole needs to be loaded by a coil. The loop ,for me, is a too small slot aerial and it needs to be loaded by a capacitor. On receive both have a small efficiency due to their small size On HF this is hiden by the high level of noise. |
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