A 2x2:2 802.11n can only hit a maximum of 300Mbps PHY at 40MHz 5GHz PERIOD. That's HT MCS rate 15 / VHT MCS rate 7. 802.11n uses a 20MHz or 40MHz wide channel only. 802.11n 3x3:3 can hit 450Mbps @40MHz 802.11n 4x4:4 can hit 600Mbps @40MHz WiFi 101 / WiFi 10 Commandments - Commandment 1. Cut through the sales BS by understanding the MCS tables and be able to read a data sheet Commandment 2. Thou shall never, ever, ever run 2.4GHz past 20MHz wide or you will be stoned in the biblical sense. Anyone claiming that a 2x2:2 can hit 600Mbps is just flat wrong an attempting to mislead you either on purpose or due to not knowing how it works. How they are getting the BS sales number is by adding the 2.4GHz @40MHz wide max PHY rate with w/ a 40MHz wide 5GHz max PHY of 300Mbps. In practicality it is super easy to hit this PHY rate, the problem is people too often think that is the throughput. IT IS NOT. This is the maximum theoretical speed the device transmits and receives the data over the air when it gets to "talk or "listen" to a client. You throughput will be substantially lower than that. A good median speed for 2x2:2 802.11n on 40MHz wide 5GHz is between 240 to 300Mbps divided by 2, because wireless is half-duplex. For 20MHz wide N on 2.4GHz it is between 115 and 144Mbps, again divided by 2. If you are connecting using any modulation below QAM64 you have other issues in your environment that you must correct and/or account for. If you aren't getting these PHY rates at QAM64 you have to look for the interfering devices on the airwaves... something is wrong. If you are getting PHY RATES using QAM64 and it still sucks.... check your cabling and interconnects. Also, make sure you don't have any rate limiting GP's applied. Note A GP will not change your MCS but it can limit your throughput.
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Check your WPA encryption mode for the SSID. Wireless>Access control>WPA encryption mode. If you've got it set for WPA and WPA2 only try change to WPA2 only (assuming you're using WPA pre-shared key for authentication type.)
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