John, I will tell you up front that I don't know crap about AIS un its or antennas, however I have spent a few years troubleshooting things. In this case I will give you the same guidance I have given my two sons. If something had been working fine for five years, and hasn't stopped working but is no longer working correctly, what is different today from when it was working perfectly? You already answered that. The solar panel. Is it possible that something else could be wrong? absolutely. Is it possible that the solar panel isn't causing the issue? Yes again. All part of the troubleshooting process. Although time consuming, I would remove the solar panel and try the system again. It either fixed the problem or not. If not, you have eliminated one possible source. You can run a new VHF cable at that point. That will either fix the problem or not. If not, you have a new cable in place. After those two obvious things, it gets pretty murky in my head........circuit boards, gargoyles?? Who knows.