I have two CPE510s 8km apart with good line of sight set up as AP and Client.  I have used spectrum analyzer to select best possible channel, set Max TX rate to lowest possible value, and am using the smallest bandwidth (5 MHz).  Transmit power is maxed at both ends and MAXtream is disabled.  Approximately every 15-20 minutes the client stops communicating for the same amount of time and then reestablishes comms on its own.  The environment is somewhat noisy but the noise is consistent.  I don't understand what could be causing a loss of comms at such regular intervals.