The easiest and cheapest way to improve your signal is to make a parabolic reflector. Go to Google with "wifi parabolic reflector" to get a template it is the first listing. I've used this, and it improved the signal dramatically. It only takes minutes, and will cost nothing. The router manufacturers should supply their kit with them, in my opinion.
That one guys gets great coverage for his property.
didn't see it here but assume you've gone to starbucks or somewhere to eliminate that it might be iPad. My house has one wall that has steel rebar and concrete in it,
I use airport extreme base station and have airport express scattered around the property.
Wi-Fi Finder App for iPhone - JiWire.com (It says its for iPhone, but it works fine on the iPad. All that means is that it does not fill the whole screen like "HD" apps)
I called Linksys today and they went into my computer threw the internet and changed it to channel 11 (which I could have done myself if Linksys or apple mentioned it). So far I have a connection which is an improvement from almost nothing. Not full bars yet but they told me to monitor the connection and are going to call me back tomorrow so fingers crossed.
I can't help feeling bad that apple returned 2 ipads and sent them back to California, but I followed everything they told me to do.
Didn't you ever try to use your iPhone to test the wifi?