Bluetooth can knock out Wi-Fi signals

Westlake Village (CA) - Have you ever wondered why your wireless connection drops or slows down suddenly during the day? With the help of Cognio's ISMS Mobile spectrum analyzer, you can identify the problem and track it back to the source. Among the devices that can drag down your Wi-Fi performance, are microwaves, cordless phones and even Bluetooth devices.

Traditionally spectrum analyzers have been large and expensive beasts, costing $10,000 and up. The ISMS Mobile comes as a PC Card and is meant for laptops. An internal antenna gathers power levels and raw radio frequencies in the 2.4 GHz and 5 GHz bands. A small external antenna is also included and users can connect bigger antennas via an MMCX jack located on the side of the card.

So what makes a spectrum analyzer better at finding problem than say NetStumbler or an open-source wireless scanner? If the interfering device is another wireless access point, then NetStumbler will be able to find the source, but often household objects are the cause of interference. In addition, NetStumbler will not detect Bluetooth devices, which in fact can greatly reduce or even eliminate your wireless internet. According to Greg Barone, sales Director for Cognio, "the product actually checks the physical layer or the air. It can track and classify exactly what offending device is."

The included software shows several charts with moving lines and curves. The two main data to track are the detected frequencies and the "duty cycle", which is the raw power being used on a frequency. Barone explained frequency could be compared to the way a water pipe works: "If one device is using more power, there is less power for the other device." Wireless access points and clients generally a group of frequencies on the 2.4 Ghz band and they are labeled Channels 1, 6 and 11. Barone showed us how other devices can play havoc with these channels.

Bluetooth devices are spread-spectrum devices and hop on 83 frequencies over the entire 2.4 GHz band. Barone told us that the typical Bluetooth device uses 5 to 10 percent of the available duty cycle, while your average wireless access point uses around 50-60 percent of the duty cycle. With enough Bluetooth devices it's possible to destroy your access point signal and Barone says, "You can imagine what will happen if there is a roomful of people with Bluetooth devices," says Barone.

Also, the everyday microwave can take out a wireless network. Barone showed off a screen capture which depicts a nearby microwave taking up 50 percent of available power levels on channel 11. In addition, Barone says that the firm's customers have found other interesting and sometimes downright illegal causes of interference. One customer discovered that the 2.4 GHz headsets used by the call center would "kill" the 802.11b connection for the whole building. Another customer discovered a wireless bridge was going through their building without their knowledge. The bridge was overpowering the company's wifi and disconnecting users from the access point.

One city tried to figure out why people were getting disconnected from their cellular phones and Wi-Fi every 12 minutes. After doing a few sweeps, city technicians discovered that a tram, equipped with Wi-Fi, was cutting the beam. Coincidentally, the tram runs once every 12 minutes. The city was able to show the tram operator the data and negotiate a different frequency. Companies often need proof that their device is causing interference and you just can't walk up to them and say, "I think your microwave is knocking out my Wi-Fi." Barone says, "With the software and card, you can record the power levels and then show them the problem."

Humphrey Cheung was a senior editor at Tom's Hardware, covering a range of topics on computing and consumer electronics. You can find more of his work in many major publications, including CNN and FOX, to name a few.