What else can I do to improve performance?

Energy radiated from a transmitting antenna is often polarized in either the horizontal or the vertical plane, so a receiving antenna will detect a stronger signal from an antenna with the same polarity. In other words, if the transmitter uses a vertical antenna, the receiving antenna will detect a stronger signal if it is also vertical. If the transmitting antenna is horizontal, a horizontal receiving antenna will perform best.

At short range, polarity won't make a significant difference to the performance of a Wi-Fi link. Even if the two antennas have different polarity, they will still exchange signals that are strong enough to keep the data moving at full speed. But when you are trying to squeeze every possible data bit out of a weak or noisy signal, you might see some improvement when both antennas are polarized the same way.

The captive antennas built into most PC Card adapters are difficult or impossible to move without turning the whole computer on its side, but many access points have antennas mounted on swivels, so it is easy to move them from a vertical to a horizontal position.

If you are using a laptop computer with an internal network adapter, the antenna is probably built into the upper half of the "clamshell" alongside the screen. You can sometimes improve wireless performance by changing the angle of the screen or by rotating the entire computer on its base. You don't have to make a huge adjustment to the screen angle; a slight change can make the difference between a poor signal and one you can use.

Can I use my access point as a network bridge?

An access point is a bridge between a wireless network and a wired LAN. If a single access point is not adequate to reach the entire area to be served by the wireless network, connecting additional access points to the wired LAN can extend the coverage area. But a wireless bridge, in which the wireless link connects two LANs together, is a more specialized device. Many access points offer wireless bridging as an option, but not as part of the basic feature set. If you plan to use an access point as a bridge between networks, check the specifications before you buy it. Your best bet is to buy a separate wireless bridge rather than trying to jury-rig a generic wireless adapter.