Wireless N is worse than G

I have the O2 Box IV (Thomson TG587n) with a Dell Studio laptop.

There is a Dell 1397 WLAN card built into the laptop which is rated as 802.11g
I purchased a SMC Wireless USB adapter which is rated as 802.11n (upto 300mbps)

The g card connects to the laptop at 54mbps and the USB adapter at 130mbps.

When using the TBB speed tester the g card downloads at 13.4Mbps and the N adapter at 9.1Mbps.

When transfering a 2.1GB file from my wired PC the g card transfers at 3.1MB/s and the N adapter at 1.8MB/s.

I had to go to the SMC web site and download and instal the Win7 drivers for the adapter to make it work as the included CD only went up to Vista.

edit: using WPA2- personal

Can anyone shed any light as to why the N adapter is slower than the G card?

Edited by broadband66 (Sun 07-Oct-12 11:44:50)

Wireless can be "funny". The USB adapter may be of low quality, the USB bus may be strangling the processor more than the built-in card is doing, etc, etc.

Check CPU usage during the speedtest etc, see if it is spiking.

There's lots of obvious things you can do to troubleshoot (change wireless security settings in case there is an issue with that USB adapter and WPA2, change wireless channel, see if the situation is the same when you are very close/far away from the router, try the USB adapter in a different laptop, try with other wireless clients d/c off the network, try changing wireless mode of operation in your router).

Diagnosing wireless problems is often more of an art than a science.