I have set up at wireless LAN network in a small office, connected to a ADSL connection.
Using a wired connection between a computer and the router, I get the expected ~8.5 Mbps down, and ~1 Mbps up. Using wireless connection, I get ~400 Kbps down, and ~90 Kbps up.
I have tried different clients, I have tried different wireless LAN routers. I have tried running 802.11g and 802.11n. I have tried resetting everything and starting over.
I can't run 5GHz, because some of the clients don't support it.
The experience is consistent across all devices.
I am convinced that I am dealing with an interference problem, but how do I find the source? I don't want to buy a $200 kit to find out, so I wonder if there is some software available that can do this.
I have a Mac, iPhone and iPad available, but I don't think there is much of this kind of software available on iOS and Mac OS X. I do have a laptop that I can install Linux or whatever onto, but I rather not have to install Windows, if I can avoid it.
How do I determine whether or not interference is causing my performance issues?