if RB711GA-5HnD support 300Mbps throughput, I expected to see mcs15What did you expect to see there? MCS data rates are the same for all 802.11n devices
You can go and see the MCS numbers here: http://en.wikipedia.org/wiki/IEEE_802.11n-2009
http://routerboard.com/pdf/330/rb711G-5.pdfWhere did you see this? From the R52n-M datasheet:
2Nss: 270Mbps @ 800GI, 300Mbps @ 400GI (Max.)
MCS7 20MHz -77 16
and why in the specification for routerboard has been written mcs7, but if 2Nss then it must be from mcs8 to mcs15?300Mbit is only possible with 2 chains. R52n-M has two connectors.
If I correctly understand, in RB711GA-5HnD two chains used for spatial diversity.all the options work, important is what you need it for