Got the Dell wireless WLAN card 1520 today.  Had some problems with the Dell driver software for 1500 series. Fortunately still had the Broadcom drivers 802.11 (agn) still on the machine. See previous response in this tread. After re-starting the computer with the 1520 card the driver software installed the 802.11N version automatically.  Connection to the router no problem, speed up from 12 MB to 50 MB. Which is 50% from the wired computers and acceptable. Most laptop computers wireless here perform  on that  level of 40-60 Mbps .  Replacing the 1397 card by the 1520 card in combination with the latest Broadcom driver solved the problem.
Computer: Laptop Dell Studio 1555 Dual Core:  W 7 64 bit, router Sitecom WL-351. Max. connection 120 Mbit.  Speed normally approx 100 Mbiton the Dell  desktops.  Connection speed on the Laptop Studio used to be 60 Mbit wireless . Haven’t checked speed for many week but yesterday foundout that the speed  dropped to 12 MB. Wired the laptop to the router, connection wend up to 98 Mbit. Wireless again the speed dropped to 12 MBit.  Checked the wireless connection with another laptop and it went up again to 70 Mbit. What could be wrong on the Studio 1555? Cleaned the computer, no malware, Mode AP, Channel 11, WPA2 The card Broadcom driver 10-01-2008, version 5.30.21.0 The card works but the 12 Mbit should be at least 60 Mbit. Any suggestions, please?
Dell Wireless card connection speed wired 98 Mbit but wireless 12Mbit.