Post date: Jul 4, 2011 2:20:27 PM
There are quite a few ways of looking for sources of interference.
For detecting all radio activity in the 2.4ghz range, for approx $100 you can buy a wi-spy unit which can pick up signals from non-wifi equipment, microwave ovens etc and give you an idea of whats in the air.
You just connect the wispy device to a laptop and move around in your coverage area or look at signals near antennas etc.
Demonstration of problems with car alarms causing interference - debugged with a Wi-Spy
YouTube video of using a Wi-Spy for debugging radio problems
A more common method that only requires a wifi card is to use Netstumbler which is a microsoft windows application. This software however will only detect wifi networks and you could be getting interference from other sources, for example wireless video senders or car alarms.