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Re: [loopantennas] G4HOL horizontal loop aerials

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  • Andy
    In my opinion, a Magnetic Loop antenna is a distinct species and they are better left alone as a separate group. Contrary to the name, and contrary to
    Message 1 of 5 , Jul 18, 2013
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      In my opinion, a "Magnetic Loop" antenna is a distinct species and they are better left alone as a separate group.  Contrary to the name, and contrary to intuition, a Magnetic Loop antenna is not one that generates only a magnetic field, or that is sensitive only to a magnetic field.  It has even been shown that many Mag Loop antennas are actually the opposite, responding somewhat more greatly to the electric field than the magnetic field.

      I believe the distinguishing feature of a Magnetic loop is one whose total circumference is much smaller than one wavelength ... perhaps no more than a tenth of a wavelength ... such that the current magnitude and phase around the loop is everywhere nearly the same.  This is in contrast to "full size" loops, quad loops, delta loops, horizontal skyloops, and such, where the circumference is usually comparable to a wavelength, or longer.  A consequence of this difference, is that a Mag Loop antenna has totally different radiation characteristics to a non-Mag Loop antenna.  The directions of maximum radiation, and of the nulls, are reversed!

      So even though a Magnetic Loop might be considered "just" a loop, I put to you that it isn't, and that it is best treated separately.

      About your question about the connections, it's a little hard to tell what you mean, and I don't have access to the article.  It doesn't make sense to connect wires from opposite ends of the feedline to the ATU and earth.  Same end only.

      Articles about the Skywire horizontal loop describe using it two ways:

      On higher frequencies (most bands), keep the two ends of the loop separate.

      On lower frequencies (usually meaning 160 meters), where the loop is too short to be an effective loop antenna, short the ends of the loop together, or the two wires of the feedline together, and drive it against earth.  What you really have in this case is not a loop antenna anymore, but a vertical antenna (the feedline), with what was your "loop" acting as a capacity hat.  It's a way of "cheating" ... getting an extra band out of that copper where it doesn't make a good loop antenna anymore.


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