Hello,Trying to send wifi thru plaster walls (no metal lathe, only wood), no mirrors, no cordless phones and only going about 20 feet. I'm trying to run signal from 2nd floor to first, thru one 4 in wall, an open stairwell, then thru a door or possibly another 4 in wall (depending on route the signal takes). My router (new) is a Lynksys "mid range" with up to 300 Mbps. It has not external antennas. Would getting a longer range router with antenna's help?
Maybe the router is broadcasting on one channel and the computer's adapter is only receiving on a different one.
Far likely, though, is the signal isn't twisting and turning the way you want it to - particularly down the stairwell - because it works in straight lines. A pair of Powerline adapters and a wireless repeater downstairs would do the trick, or the powerlines themselves could provide a wired connection down there.
Plaster walls shouldn't block the signal but there is a limit to how far the signal can travel. The signal will loose the power going through one plaster wall and more through the second.
Your best bet would be a either power line kit or a wireless extender on the second floor.