Question : Problem: wireless router signal doen´t reach downstairs, what is the best way to enhance the signal ?

WIRELESS ROUTER, zYTEL, WORKS PERFECTLY BUT SIGNAL DOESN´T REACH OTHER FLOORS OF THE HOUSE.  HOW CAN I AMPLIFY ITS SIGNAL.

Answer : Problem: wireless router signal doen´t reach downstairs, what is the best way to enhance the signal ?

The ''best way'' would be to run ethernet cable to the other floor[s] and install extra access points where there is no signal.

2nd best is adding higher gain antennae to the router and or clients.

3rd best is adding wireless repeaters (major drawbacks are each hop cuts speed in half, and some repeaters work only with their own brands of wireless routers)... even though 3rd best, rare is the internet connection that can saturate even an 11b signal when cut in half... but if the intent is also to have an effective LAN then this is the worst choice as it might give lowest throughput between clients on the LAN.

The antenna option makes it to #2 on my list only because it generally costs much less than adding more devices like repeaters or bridges. Not all wireless routers/APs have replaceable antennae, though. Those that do might have different types of connectors on different brands.

If you can move the current router to a central location and position the antennae close to horizontal and at 90 degrees to each other (horizontally), instead of them being vertical and parallel, it should better-penetrate floors and ceilings but will not spread as much in the direction they are 'pointing' on the floor the router is on. i.e. the signal emanates radially from stick antennae... having them at a right angles to each other will help spread the signal somewhat on that floor, but there will still be 'blind spots' - in the direction the 'V' points as well as smaller dropoffs in each direction the tips point. If there is only one antenna this is really not a good option, either.

Hope that helps.