Possible reasons:
1) Antenna position
2) Interference
Check if there are appliances that could interfere the signal.
By the way, the signal strength you mentioned on your computers are good. If you're not experiencing internet disconnection, then I think you're fine.
Good questions. 1) yes there is some interference from heating ducts. The router is also located within 3 feet of the circuit panel for the house. 2) I've moved the antennas every which way till sunday, with no change.
This having been said, let me clarify set up.
Prior - Router in room in front left corner of house. Main desktop in next room separated by solid wall (aluminum duct work through wall) signal strength upper 90%. Upstairs 2 desktops and a laptop. Any one of these computers signal strength 50 - 73%. All three computers have wireless n cards, (a mix of manufacturers) These three upstairs are in separate rooms all directly above the routers location.
Present - Router moved to basement directly below prior location. Big changes though with signal strengths. Now, on first floor desktop, signal has dropped to between 60 - 72% while the three on the next floor up have increased to the 90's.
I understand you feel this is still good however, things are noticeably slower. I have the ability to get a second DIR-628, would it be beneficial to use the second one as a repeater?
Thanks, Tom