Raymarine Ray60 VHF and AIS troubleshooting

[B4A]

My buddy has problems with his VHF and AIS. I can hear him well and see his boat on my screen when he's in the 2 or 3 nm radius out in open ocean.

Over that distance, the VHF communication degrades significantly and he disappears from my screen.

I can see other ships on my screen that are over 10 nm away, but can't see him at 4 nm distance, so the problem is not my instruments, but his system.

We have checked that his VHF is on 25W mode, we checked all the connections and the antenna up to the mast. Everything seems to be in order.

What else can we do to troubleshoot the problem? We are in remote areas of Brazil, so no Raymarine or VHF technician is available.