Issue: The device overview shows that my devices are not connecting at full speeds. 802.11n throughput depends heavily on 40MHz channel width and additional antennas.
The iPad 1 is in compliance with 802.11n but delivers only slightly better performance than previous 802.11g.
Root cause: 40MHz in 2.4GHz bands is often deactivated because of interference with other channels. There are only 3 20MHz channels without overlapping available in the 2.4.GHz band.
Solution: For a complete table see IEEE_802.11n-2009