New Airport Card - still no/bad reception

Try carefully cleaning (no power attached) the slot and ends of the card. A pencil eraser on the ends of the card is abrasive enough to clean off oil or corrosion... plugging and unplugging the card a half-dozen times should clean the connector. Examine that the connector is not breaking loose or has solder joint cracking

The antenna wraps around the display (study the guide) It can be replaced... but that is a major DIY project. Check that the antenna is not damaged where it passes through the clutches (hinges)

You could try an external antenna on the router or, on your laptop.

There are many variables that affect wireless reception... For example, if you have a new router and an old laptop the router may not broadcast on 802.11a/b/g by default OR if it's an older router & a new laptop it may not broadcast on 802.11g/n at all.

The threshold and beacon interval of the router may need to be adjusted.

If there are other routers, or wireless devices you may have to try changing channels.

If there's heavy traffic on the router signal may diminish

If you live in an old building the wiring of the building, microwave ovens, motors, hand held cordless phones could provide interference.

The composition of the floors, walls, plumbing/heating in the walls could provide interference.

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