Wireless Bridge, Problem with transfer rate

Hello, I have a wireless link over 2km. Board RB411, Card R52hn, an dualpolarized Flatantenna with 21dbi on both sites the same hardware.
The problem is the following…
See the graphics:
First time tx/rx rate 300Mbs/270Mbs
second_one.jpg
one second later 300Mbs/6Mbs
one-second-later.png
and this change all the time.
So there is my actual config:

/interface wireless
set [ find default-name=wlan1 ] adaptive-noise-immunity=client-mode band=\
    5ghz-onlyn channel-width=20/40mhz-ht-below country=germany disabled=no \
    ht-ampdu-priorities=0,1,2,3,4,5,6,7 ht-rxchains=0,1 ht-txchains=0,1 \
    hw-protection-mode=rts-cts hw-retries=15 l2mtu=2290 mode=bridge \
    security-profile=BBS ssid=BBS-50M_BR tx-power-mode=card-rates
/interface wireless nstreme
set wlan1 enable-nstreme=yes framer-policy=best-fit

and the same at the station bridge site.

The real transferrate is only 23Mbs, is too slow… and I think, i have a problem, but i dont know, whats the problem.

Please help

Thank you

Try this settings

http://www.wirelessinfo.be/index.php/mikrotik/pages/omnitikpp

Its with other device but is the same configuration

Great,… thank you it solves the problem

Thank you very much

Great
If i help you give me karma pleace