A six kilometer link using Cisco 350 bridges. The signal strength appears to be relatively stable (48 to 54%). A linktest shows 100/100 at 11Mbps and very few retries. The remote appears to be deassoc/deauth then auth/assoc every few seconds as the logs from the root show.
2006/09/30 09:42:32 (Info): Station [wbwpge02]0040965364cb Reassociated
2006/09/30 09:42:32 (Info): Station [wbwpge02]0040965364cb Authenticated
I had a similar problem, link quality was good but continual reauthemtications between the bridges. In the end it turned out to be a faulty bridge, we'd tried updating firmware and various other things but a new bridge sorted the problem.