I've got a Netgear DG834GT wireless router down stairs but PCs are upstairs on other side of house. Connection between PC and router is not very good. Thinking of fitting a 7dB high gain antenna (various ones on market, haven't yet decided which one). Before I slip out my credit card, just want to know if this is a worthwhile investment. Moving the router is not an option, nor is moving the PCs - I need a wireless connection.
The signal coming from your stock antenna is shaped like a donut slipped onto the antenna. You want it broadside to the target, not pointing end-on, like might be typical if the downstairs antenna were pointing straight up.
You could add a simple reflector. If you get some signal at the PCs now, this could give you substantial boost.
EZ-12, printed on photo paper for thick stock, with aluminum foil glued to the sail, provides a substantial boost in signal.
The signal with the reflector is not only 13dB stronger, it's more stable.
You probably want a directional antenna. I have used the "Hawking HAI6SDA Directional 6dBi 2.4GHz Antenna" with good success on a Netgear WG311 PCI card. $20-30.
The one I bought fit the Netgear, and had an adapter that fit RP-TNC.
You could use one or more of these on the router and PCs. The omni antennas improve gain by squishing the donut. It gets flatter, and harder to aim, until it looks like a frisbee instead of a donut (thickness and diameter in ratio as gain goes up). But you are still wasting signal in the other directions on the frisbee.
A corner reflector has more height, but less beamwidth, like a slice of cake.