Signal is good, the coverage zone is good as well.
But, the Tx level in the wireless registration on RB751 is bad, despite the good level of signal (aprox -55). The RX level in RB751 is Ok, like other radios (R2HN and RB711), but TX level is not good.
.... CCQ is bad and transfers data velocity is very unstable. The client is disconnected frecuently.
I have seen very similar problems with my router. It doesn't matter a card, running operating system (driver) - especially when the client doesn't send a long time larger amount of data, TX signal falls and wlan card driver (I think) recognizes the link as disconnected (this fact is sometimes recorded in the router log, but more often seen as a loss of connection on the host). A little bit annoying, comparing to running in this place earlier TP-Link router with DD-WRT there was no objection....