Ok, so on my work machine, during the day I generally get a good connection with max bandwidth around 144.0 Mbps. However, sometimes at night, for no reason, when I'm using FTP to upload it drops down to 1.0 Mbps. Here's the funny thing: It only drops to 1.0 Mbps when uploading on FTP. If I stop the transfer, it (usually) climbs back up to normal. Checking for interference using inSSIDer doesn't find anything that might be a problem. The channel I'm on is mostly free with no strong signal interference, the second strongest signal that might interfere is nowhere near my channel at all. I'm using an external Asus USB N14 with two antennas, so I've tried repositioning the thing all around but not much help. Weird...
Hmm... never encountered such problems before. I don't think there's anything else that you can do other than trying another USB WLAN adapter?
