hi all
I have a 16km link 2 RB 600 ppc 3.10 with 2 XR5 600 mW with 90cm dish gain 31dB.
The signal is excellent-45/-48 dBm and signal to noise about 56.
The RB600 mode is ap bridge / bridge Turbo mode 5 GHz.
The problem is the throughput is very low about 6Mb/s Maximum.
the link ping is 1 ms when its 5 Mbit/s or less and the link 54Mb/54Mb or 48Mb/48Mb
but when the load reach 6 Mbit/s the ping will go high about 500 and the link will be 6Mb/6Mb or 6Mb/9Mb and the throughput will be less than 3 Mbit/s
from the registration table we see :

interface=wlan1 radio-name="00156D640F10" mac-address=00:15:6D:64:0F:10 ap=yes wds=yes rx-rate="48Mbps*2"
tx-rate="6Mbps*2" packets=1810997,1761683 bytes=230138855,1540657708 frames=1810997,1761683
frame-bytes=219284315,1530087610 hw-frames=2262648,1764188 hw-frame-bytes=325879019,1572465554 tx-frames-timed-out=0
uptime=41m34s last-activity=0s signal-strength=-49dBm@6Mbps signal-to-noise=54dB
strength-at-rates=-49dBm@6Mbps 90ms,-46dBm@9Mbps 1m25s440ms,-46dBm@12Mbps 1m14s100ms,-46dBm@18Mbps 24s240ms,-
46dBm@24Mbps 11s130ms,-50dBm@36Mbps 11s110ms,-53dBm@48Mbps 0s,-52dBm@54Mbps 20ms
tx-signal-strength=-46dBm tx-ccq=47% rx-ccq=90% p-throughput=5998 ack-timeout=204 nstreme=no framing-mode=none
routeros-version="3.10" last-ip=87.248.104.105 802.1x-port-enabled=yes compression=no wmm-enabled=no

and the wireless setting is:

0 R name="wlan1" mtu=1500 mac-address=00:15:6D:64:4E:C2 arp=enabled interface-type=Atheros AR5413 mode=bridge ssid="IRAQ"
frequency=5800 band=5ghz-turbo scan-list=default antenna-mode=ant-a wds-mode=static wds-default-bridge=bridge1
wds-ignore-ssid=yes default-authentication=yes default-forwarding=yes default-ap-tx-limit=0
default-client-tx-limit=0 hide-ssid=no security-profile=default compression=no

i think its clear
thank you in recent for your reply

activate nstreme, disable csma, compression on. You should get 70mbps.

Don't enable compression but do enable nstreme.

Your signal is too strong. Lower output power to be in the -60 area.
Imagine someone screaming directly into your ear - you hear them, but don't understand.

Thank you all
i tried to reduce the signal power and i found advantage in throughput and the link is good now.
i will try nstreme later
thank you all again for your support

Just curious, do you have a 31db dish on both sides of the link?

yes i have 2 dish 31 dB on both side and the signal strength are equal in each side