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.
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.
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.
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.