Quick Tips

Visualizing microwave oven interference

Many of you probably know that a microwave oven (MWO) operating near a wireless LAN can cause throughput to drop. In case you haven’t seen what MWO interference looks like on a spectrum analyzer, see the image below. This measurement was taken about five feet away from a MWO oven cooking a bag of popcorn, which takes about two minutes. As you can see, the majority of the interfering signals fall within the top half of the 2.4GHz band, especially around channel 9. What’s seen in the image is actually an average of the interfering signals. Instantaneous signals were much higher in magnitude. To dramatically improve performance, access points within range of a user near the MWO should avoid channels 6 through 11, especially channel 9. As a test case, I tuned the nearby access point to channel 9, and Internet browsing from a wireless laptop within ten feet of the MWO was completely blocked by the interfering signals during the entire time that the popcorn was cooking.