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Should I or should I not replace an aluminum wire (defective) with a copper wire on a Hy-Gain LP-1010 log periodic ham radio antenna which is made entirely of aluminum with stainless fasteners? There is a wire connecting each element to the boom. This is a 14 element antenna requiring 28 paired wires.

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  • $\begingroup$ Tell us a bit more about the antenna please. Are you sure it's a log periodic? An LPDA has two booms, connected alternately. How big is it physically? Aluminium wire would be very unlikely on a small antenna unless you refer to the actual 3/16" wire elements... Huge antennas do use aluminium (or copper) coated steel wire. $\endgroup$ – tomnexus Jan 21 '15 at 19:53
  • $\begingroup$ Also, how did the wire fail? A picture of the antenna and a detail of the failed wire would be great. $\endgroup$ – Phil Frost - W8II Jan 21 '15 at 19:55
  • $\begingroup$ Comment #1 re: tomnexus' reply - this antenna is a Hy-Gain Log Periodic LP-1010. It is a 14 element antenna with a 36' boom, 2" diameter, on top of a 50' tower. Longest element is 48' 11". The wire is 12 gauge stranded, is 'silver' in color, connects each of 2 tubular feed-lines alternately to each of the elements. My best guess is that this wire is aluminum. I bought this antenna used from the widow of a ham that had died, and have not checked with the company about the type of wire used. $\endgroup$ – David Jan 22 '15 at 1:19
  • $\begingroup$ Comment #2 re: Phil Frost's reply. The wire may not have 'failed'. I was confronted by a decrease in Tx and Rx when talking to station in Hawaii, and was looking for ALL possible causes. On checking all the wires from boom to elements, I found this one that had a small 'nick' in it, and thought I would replace it. I thought this was probably not a cause, but "while I was there, I would replace it". The electrical store had just the copper wire. Sorry, don't have a photo to send (and don't know how to attach a photo to this note) $\endgroup$ – David Jan 22 '15 at 1:27
  • $\begingroup$ @David Upload the image to imgur or something else and edit the question to link to it, and someone will stick it in for you (which you can do yourself after you get a little rep) $\endgroup$ – Phil Frost - W8II Jan 22 '15 at 12:57
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The wire is probably tinned copper, not aluminium, but the material is not critical to the function of the antenna.

You could replace it with any other wire of similar thickness, but keep the length and shape of the wire exactly the same (within 1 or 2 cm) to avoid affecting the antenna design itself.

Take all the usual corrosion precautions at the junction: lightly sand the aluminium immediately before installing the wire. Use stainless steel fasteners. Apply a bit of grease to the joint. You should probably read up some more on best practice.

While you're at it, check, clean and tighten all joints between pipes and to wires.

Your sudden loss of signal might be the antenna, or something else. A problem with an LPDA is easiest to see in the VSWR; at frequencies near the resonant length of the faulty element the VSWR will shoot up. Test it at both ends of each band and see that it performs as expected. If you have a long feedline, you can do some maths to find the VSWR at the antenna, from the VSWR in the shack. In my experience you can test an HF LPDA on the ground, just pointing it up to the sky, or even lying flat on the ground if you have fairly dry soil. Keep it away from long metal objects of course. It won't give exactly the same result as on the tower, but surprisingly close, and good enough for fault finding.

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  • $\begingroup$ To tomnexus, thank you for your input. Helpful. $\endgroup$ – David Jan 22 '15 at 14:42
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I don't think such connections have anything to do with its function as an antenna. I think they're just there to make sure there's a DC path to ground for dissipating static electricity.

As such, I would not recommend using copper for these connections, because the copper will corrode, long term, and the galvanic interaction between the two metals will accelerate any corrosion. Stick with aluminum.

You can get short lengths of aluminum wire by buying a few feet of heavy-gauge power wire (the type used at the service entrance) at a hardware store and pulling individual strands out of it.

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  • $\begingroup$ Wouldn't it be the aluminum that corrodes, aluminium being the more anodic metal? Also, if galvanic corrosion is a problem with copper, why isn't it a problem with stainless steel? $\endgroup$ – Phil Frost - W8II Jan 21 '15 at 18:41
  • $\begingroup$ When exposed to the air, aluminum quickly forms a nonconductive oxide layer, reducing its susceptibility to further corrosion. Copper oxides do not form this kind of "passivation" barrier. $\endgroup$ – Dave Tweed N3AOA Jan 21 '15 at 19:03
  • $\begingroup$ Sure, but galvanic corrosion doesn't corrode both metals: it just corrodes the anode (which is why sacrificial anodes work), and I don't think the aluminum oxide layer means aluminium is impervious to galvanic corrosion. aluminiumdesign.net/design-support/… $\endgroup$ – Phil Frost - W8II Jan 21 '15 at 19:43
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    $\begingroup$ @PhilFrost: I really didn't come here for a debate. I'm just trying to explain why they used aluminum wire on the antenna in the first place, and why it's a good idea to replace it with the same. If you have a better answer, by all means, post it! $\endgroup$ – Dave Tweed N3AOA Jan 21 '15 at 19:51
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I've home-brewed several LPDA HF antennas, each one bigger than the last. I don't think it would be a problem replacing with same gauge/length of copper stranded. Another place to look for poor connections on the Hy-Gain LPDA, are joints along the small diameter phasing line. A pair of them run the full length of the boom and the short wires connect the tubes to the elements. I know of a TH-11 that had that problem, corrosion in the joints. Same style of feed/phasing lines. Match/SWR went crazy!!! I cleaned the joints up, used some conductive compound, reassembled the antenna, and was back in business.

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