Scott in Aztlan writes:

Since my WiFi card is built into my laptop, to use a directional antenna will
require disabling the internal WiFi card, buying a new PCMCIA card with an
external antenna jack, and buying a directional antenna - expenses I'd hoped to
avoid, but which now appear necessary.

If you want to try this with the internal antenna, you should be aware
that it is probably *far* from omnidirectional. Even if the antenna
design itself is something that would have an omnidirectional pattern in
the middle of an open field, the proximity of other metal within the
laptop itself will mean that the pattern "in situ" is far from
omnidirectional. You can see this to some extent by just rotating the
laptop while sitting in one place and watching the RSSI change.

Then when you put that laptop inside a car, the car will further modify
the reception pattern.

Dave