What is the longest distance rb411 can do?

RouterOS Wireless Networking
1

i am trying to connect a client who is 15km away from the base station with a 411rb and a r52 wireless card but it does not see any of the interfaces at the base station. Do u think i can make it?

2

Yes, no problem, but you will probably need better antennas. what antennas are on both ends now?

3

5ghz at 8dbi

4

you need better antennas, look at the calculator: http://www.mikrotik.com/test_link.php,
it shows that your link is not possible until you increase antenna gain

something like this will make it possible: http://routerboard.com/pdf/ric522c.pdf (22dbi)

or you could switch to R5H cards and then even a 14dbi antenna would be enough.