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My Hy-Gain TH6DXX antenna has been up on a tower about 20 years, with excellent results. Suddenly, the gain of the antenna is off the side; in other words, when the boom is broadside to the transmitting station, and the element ends are pointing at it. Just 90 degrees off of where it has been and where it should work. This is verified in any direction.

The SWR of the antenna is excellent. I have tried different frequencies in the different bands and the results are the same.

Anyone have any guesses to what has happened?

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  • $\begingroup$ Welcome to this site, Mell! Couple of questions: 1. Is it possible that the antenna and/or mast slipped 90° in relation to the rotor? 2. Are you relying on the rotator control box direction indication, or have you actually seen which direction your beam is pointing? $\endgroup$ – Mike Waters Sep 12 '19 at 17:23
  • $\begingroup$ I have taken the liberty of adding your callsign to your profile. Here on Stack Exchange, we don't put signatures on posts — the user card automatically provided at the bottom is your signature, and you can put whatever you like in your name and profile. :-) $\endgroup$ – Mike Waters Sep 12 '19 at 17:27
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I would suggest that one of the transmission line connections to the antenna, probably the earth if you are using coax, has become disconnected at the antenna feed point, and it's just a coincidence that the SWR is still ok.

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  • $\begingroup$ I don't understand your answer. Am I missing something obvious? It sounds like you mean if the coax shield came loose, then the antenna would have the same pattern but 90° to the boom. $\endgroup$ – Mike Waters Sep 14 '19 at 2:14
  • $\begingroup$ @mike, yes that's what i mean, if the antenna is truly directional off to the side and it's not a rotator problem, i can't see what else could possibly cause that. $\endgroup$ – Andrew Sep 15 '19 at 0:07
  • $\begingroup$ But why would that happen? $\endgroup$ – Mike Waters Sep 15 '19 at 0:36
  • $\begingroup$ @mike perhaps: the boom is excited and radiating. A 6-element beam has its driven element quite far from the centre. If one half of the DE became disconnected, perhaps the boom is then driven against the other. Though in my experience the "yagi mode" is easy to excite and radiates readily. Witness the cheap yagis that use an asymmetrical/unbalanced gamma match to feed one half of their DE against the boom... $\endgroup$ – tomnexus Sep 15 '19 at 6:24
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I can think of two possibilities.

  1. The antenna and/or mast slipped 90° in relation to the rotor
  2. The rotator control box direction indication is 90° off. This could be caused by the pot in the rotor itself, or something inside the control in your shack.
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