Networking – Wireless network speed is slower than the maximum in Windows 7

I have a Dell Inspirion 5520 that has Intel(R) Centrino(R) Wireless-N 2230 built in.

Also I have a TP link TL-WR740N wireless router.

I have an 80Mbps/25MBps internet connection.

My Speedtest result with no router:

When I connect all these via an Ethernet cable, I get the maximum even through the router:

But when I try to do the same with WiFi I get 30/20 Maximum speed, and I'm sitting next to router!

I have this configuration:

router:
– Channel: auto
– Mode: 11n only
– Channel width: 40Mhz
– Max Tx rate: 150Mbps
– Enabled Wireless Router Radio
– Enabled SSID Broadcast
– Security: WPA- AES
– Beacon Interval : 100
– RTS Threshold: 2346
– Fragmentation Threshold: 2346
– DTIM Interval: 1
– Enabled WMM
– Enabled Short GI

Intel(R) Centrino(R) Wireless-N 2230:
– 802.11n Channel width for band 2.4 : Auto
– 802.11n Mode: enabled
– Ad Hoc Channel 802.11b/g: 1
– Ad Hoc QoS Mode: WMM enabled
– Bluetooth(R) AMP: Enabled
– Fat Channel Intolerant: Disabled
– Mixed Mode Protection: CTS-to-self Enabled
– Roaming Aggressiveness: 3. Medium
– Transit power: 5. Highest
– Wireless Mode: 802.11b/g

I do get the fact that speed through wireless is slower than with wire, but losing 50Mbps is a bit too much!