Posted: 12/6/2014 6:33:34 PM EDT
I think the balun on my dipole is full of water  I'm working on putting up an 80m loop. 14 gauge insulated wire fed by 450 ohm ladder line. I know the 1005/f - 4% calculation for length! but does the feed line count as part of this calculation? The guy in this article implies that it does... http://www.k5rcd.org/hor%20loop%20instruct.htm Mine will be a triangle with one side bowed out. I've got 105+95+58 ft legs for 258 ft if strung tight as a banjo. Adding slack ought to get it close. The feed line will be about 35-40 ft... Thoughts? |
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I am probably too naive in my approach, but when I put my 80m horizontal delta up I figured resonance was not a big deal. I was going to use it for multiple bands via a tuner so I just wanted to put it in the ball park. I used enough ladder line to reach the intended feedpoint then ran scans on the bands of interest. I ended up adding to the loop length twice, then reducing it a bit to get it to a profile I could live with.
Both full wave loops (160m & 80m) ended up with more wire than the formula called for. The 160m because I could only easily raise it totally once & heard more was better than too little or just enough, the 80m because the graphs looked better that way. At present, both transition from 4" ladder to coax via a current balun (9:1 for the 160m, 4:1 for the 80m) for connection to the TS-590 (160m connection using about 2' of coax, the 80m about 30'). Both tune OK via the internal tuner. The balun ratio was chosen empirically by seeing which one produced the best overall profile. Balanced feeds on a loop should not be radiating... Nick |
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Well, did something wrong. I hung the thing up, in the shape of a 275' trapezoid. Soldered the ladder line to either end of the wire loop and ran it into the shack (thru a piece of PVC that penetrates the concrete). Hooked the ladder line up to a DXE 4:1 balun, then coax to the swr analyzer.... It's off the charts. Like a zillion ohms of impedance and infinite SWR at every frequency. It got dark, so I cant pull it down to see what's wrong. it's pretty simple, really. Even if I had a dead short I wouldn't think it'd act like this. Any ideas? |
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I think a dead short right at the analyzer would make it read like that, unless the analyzer has a problem instead. ETA: Except a dead short would be zero instead of a zillion, but infinite SWR everywhere would still happen... :)
Might be the coax from the analyzer to the balun. Might be the balun. Might be something else. What if you temporarily connect the ladder line to the analyzer ? Should be able to rig something temporary up, what does it do then? Divide and conquer, process of elimination. |
I used to use an 80 meter horizontal loop, I ran balanced line all the way to the tuner. No analyzer, not much in the way of calculation on length. Just string it up and go! 
Feed line shouldn't be figured as part of the antenna. Just try to avoid using a feed line in resonant lengths if you can. |
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I tested everything I could think of. Eliminated everything and the meter readings still made no sense. So I put it all back together and just for s&g I hooked it up to my rig. Heard plenty of QSOs on 20. Hit the tune button with my fingers crossed that I wouldn't let the magic smoke out. Tuned up in <2 sec. Same thing on 40 and 80. Conclusion? I'm very near a local fm broadcast tower. I think some harmonic is being picked up by the swr analyzer and freaking it out. The antenna works fine Thanks for all the help guys.
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