This is my first post so I am hoping I have put it in the correct section.
I bought my first Pi (a 512MB model B) about 10 months ago, it very quickly became my media player (running RaspBMC) so it wasn't until a few days ago, when I purchased a second unit, that I've had the opportunity to try out some other things. My RaspBMC unit has been successfully running with an Edimax EW-7811Un WiFi dongle (which I had noted had been recommended by other Pi users) so when I bought my second Pi I naturally opted for the same WiFi adapter. I am using a Logitech K400r wireless keyboard/trackpad on this new Pi and both units are powered by 1A rated HTC power adapters. My RaspBMC unit has barely missed a beat in the time it has been running, but I have encountered an oddity on the new set-up which has baffled me somewhat.
When I first ran the Raspian distro (downloading the latest build from the web site) and loaded the desktop I used the WiFi application to configure the Edimax adapter. I connected to my access point (sitting no more than 5 feet away) and I was then able to connect to the outside world. About 5 minutes later this stopped being the case. Nothing suggested the Pi was malfunctioning but, when I ran a terminal session a looked at the output of "ifconfig" I could see that the wlan0 interface no longer had an IP address associated. Moreover the WiFi app no longer appeared to recognize the device.
So I re-booted the Pi. Immediately after logging in I ran "ifconfig" again and was able to confirm that wlan0 was once again running with a live IP address. I could run ping and DNS tests to confirm that all was well. I then loaded the desktop again and was able to load Midori and browse the web - for a few minutes. Again after looking at a couple of web pages all my requests began to fail. Once again, a quick visit to the terminal highlighted that wlan0 was, again, lacking an IP address. Another re-boot, and it was the same all over again - from the CLI all was well, when the desktop first loaded, all was still well and then 3-5 minutes later nothing.
I re-booted again before going to bed and left it running overnight.
12 hours later with the Pi still in CLI mode, I am still able to ping its IP address and (because I had enabled it in raspi-config) access the SSH server.
Can anyone offer any explanation as to why I lose WiFi connectivity a few minutes after loading the desktop, or offer any suggestions as to what I can look for to see what may be happening so that I may pursue it further with the community?
Many thanks in anticipation.