Hi all, My last antenna experiment was a center-fed zepp cut for 80 meters. (Dipole fed in the center with 450 ohm feed line, requiring a tuner.)
I found this antenna to be a decent multi-band antenna, with one exception: I never could get my MFJ manual tuner to find a match on 40 meters. For the other bands, it seemed to find a match fairly easily. As I had another antenna -- an inverted L vertical -- for 40 meters, I shrugged this off as something to look into later. Well, my inverted L has succumbed to the elements and I need to rebuild it, so I turned my attention to trying to figure out my center-fed zepp 40 meter problem. After much research (remember, I'm a beginner at this!), the problem has become somewhat obvious. One drawback to a center-fed zepp, I have learned, is that the impedance at the second harmonic of the lowest frequency will be very, very high. The second harmonic of an 80 meter antenna is 40 meters. Oops. Apparently the impedance is so high the MFJ tuner can't match it. I thought about purchasing a fancy tuner, but I remembered that tuners aren't miracle devices. They don't change the impedance of the antenna and I am concerned about power loss at the tuner. It seems the only thing to do is to find a way to temporarily electrically shorten the dipole when I want to operate on 40 meters. The 'zepp is an inverted V, so the ends of each leg of the dipole are fairly low to the ground and easily accessible. (They actually run along the top of my backyard fence for about 15 feet on each side!) What if I coiled enough of the wire such that the second harmonic of the new length was off the 40 meter band? Is coiling the excess wire enough to electrically shorten the antenna, or do I really need to run the excess wire back along the elements (parallel to them) for this to work? I like the coiling idea as I could just uncoil the wire on each end, stretch it back to its original length when I want to operate on 80 (or 60) meters. -- /*/-=[Michael / KT5MR]-=/*/
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