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Roy Lewallen wrote:
Tony Giacometti wrote: it is a shielded loop and no the gap is there, thats why I am wondering why its not doing what I thought it would do. What you've done is to build a truly shielded loop. The notion that a shield somehow blocks the electric field and lets the magnetic field through is a folk tale -- an intact shield like the one you built blocks both electric and magnetic fields. (Good thing, too, or else coax cable wouldn't do its job.) You've just done an experiment that proves it. The gap in a so-called "shielded loop" provides a path for current outside the "shield" to get inside. The net result is that the outside of the "shield" is just an ordinary loop antenna, and the gap acts like a feedpoint to get the current inside where it can get to the receiver. It responds to normal electric and magnetic fields exactly like an unshielded loop. What the "shield" buys you is improved balance, which helps prevent the feedline from becoming part of the antenna and picking up local noise which you can null out if balance is good. Roy Lewallen, W7EL Roy, I don't fully understand why you made this response to me. You mentionI built a truly shielded loop. How so? I did exactly what the directions called for including having a gap. If these loops are a folk tale, other than using a beverage which I don't have the room for, how am I going to reduce the noise enough to be able to woprk 160 and 75 meters effectively? |
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