Based on the security used, you appear to be in a proper backwards compatible configuration. In this configuration, the highest speed you will get with the Inspire is 65mbps. You could try switching the channel to 6 and then 11 to see if either helps, but that is not likely. I had the exact same problem as you because I had my router in a room in an extreme corner of my home. With my previous router, which was strictly wireless-b/g, I didn't have an issue. It wasn't until that router went out and I bought my wireless-n router that I started having an issue. I had to run a cable to relocate my cable modem and router to the living room, but once I did this, my issue went completely away. As I previously stated, with wireless-n, location is more critical. Having walls between your thirty feet would only compound the issue. It is still possible that you may have a source of interference in your home that could be causing the issue. In my case, I could not locate such a source. Although, I was suspicious of the digital meter outside my home that was backside of the router. The meter itself would not cause interference, but they do have a wireless chip that tries to communicate with a thermostat and appliances that have a similiar chip. You may have some source of interference or it may be strictly a location issue.
Sent from my Desire HD using Tapatalk