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Many of us use 1 wl horizontal loops configured in a square or rectangular
shape. When these loops are operated at frequencies greater than the fundamental, the horizontal pattern changes from a nearly circular pattern to one with lobes & nulls. For example, if I operate a 60' high, 1 wl, side fed, square, 80 meter horizontal loop on 40 meters, the horizontal pattern is that of a 4 leaf clover with four fairly broad lobes and four nulls. Now this is great if you intend to QSO with a station in the direction of a lobe but not so great if your target is in the direction of a null. Now if I move the feed point to an adjacent side of the square, the lobes become nulls & the nulls become lobes. In essence, I have "rotated" the pattern by moving the feed point. I have attempted to take advantage of this shift in pattern by erecting a 160 meter loop that "floats" in pulleys at the corners. I then tried to physically drag the loop wire through their supporting pulleys & move the entire antenna wire until the feed point was where I wanted it. This was a really stupid idea & did not work out due to the weight of the wire, binding at the pulleys, mechanical problems, the hassel of "rotation" , etc., etc. & I have abandoned this idea. I'm thinking now that I should just add a second feed line on a side adjacent to the original fed side and simply select the feed line (and pattern) that suits my operating needs. Like this: ********************************** * * * * * * * * * * * * * * * X * Feed (1) * X * * * * * * * * * * * ***************XFX****************** e e d (2) My problem is that I'm not sure of the effect of adding that second feed line. Should the unused feed line be grounded or simply left unconnected at the transmitter? Or should I use relays at the feedpoints to "jumper" the unused feedline? I use 450 ohm "window" type ladder line. Or, as another ham has suggested, put up a second loop, spaced a few feet down from the first loop, & feed it where I like. My goal is an antenna that covers 160- 17 meters, & has some capability to steer the "gain" on the frequencies greater than 2.0 mc. Any help/comments will be appreciated. |
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