I stumbled across a great YouTube video demonstrating co-channel interference. He is using Iperf as a throughput utility. If you would like to do similar tests, check out our Free Wireless Troubleshooting Tools page.
Remember, it isn’t just the access points causing the slower connection, it also includes all of the clients connected to each access point too.
Visually, Chanalyzer helps us understand the modulation types used by the access points. When they turn on Iperf the access point jumps into the ERP-OFDM (or 802.11g) modulation. You can see the lack of channel usage when the user changes the AP to Channel 6. Their AP is forced to wait for an opportunity to transmit. The user has another similar video where their AP jumps into 802.11b.