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David Sanchez
David Sanchez

Many Of The New Cordless Phones Operate At 2.4GHz Like A Microwave Oven. Are We €?

Avoid putting your gateway or router in cramped spaces or next to anything that can block the WiFi signal. The best position is in an open space away from thick surfaces (e.g., concrete walls) and other household electronics that may cause interference with the WiFi signal, such as baby monitors, cordless phones, microwave ovens, refrigerators and Bluetooth-connected devices.

Many of the new cordless phones operate at 2.4GHz like a microwave oven. Are we …

Many of the cordless telephones and baby monitors in the United States and Canada use the 2.4 GHz frequency, the same frequency at which Wi-Fi standards 802.11b, 802.11g, 802.11n and 802.11ax operate. This can cause a significant decrease in speed, or sometimes the total blocking of the Wi-Fi signal when a conversation on the phone takes place. There are several ways to avoid this however, some simple, and some more complicated.

Can a cell phone interrupt my connection?A cell phone probably won't interrupt your connection, however there are cordless phones and microwave ovens that operate within the frequency range of the Chicago Wireless Internet Zones (2.4 GHz and up) that can cause interference with the connection.

Radio signal interference causes wireless clients and access points to hold off transmitting, which causes delay and reduced throughput. As a result, interference lasting for longer periods of time (referred to as duty cycle) will cause more damage to the signal, and interference present for shorter periods of time may have less impact on the signal. The resulting decrease in performance caused by interference can make browsing websites and downloading files sluggish and severely limit the number of active voice users. In cases where interfering signals are strong enough, the wireless clients might not be able to access the WLAN at all for an indefinite period of time. This is rare but possible. As a result, companies need to be aware of potential sources of radio signal interference, such as microwave ovens and cordless phones, operating within the WLAN environment.

While holding the wireless client device (a laptop) within 1 foot of the microwave, we recorded some signal measurements while the microwave was set to high and heating up a large bowl of water. The throughput fell to 90 pps. As a result, using a wireless client device very close to the operating microwave made the throughput plunge by over 85 percent. This is a substantial reduction in performance, but it is the worst-case situation. The access point was set to the same frequency of the microwave oven, and it is unlikely that someone would use a wireless client so close to the oven.

A more realistic distance from the microwave is from one of the break tables, which is about 8 feet away from the microwave oven. At this range, we reran the throughput tests and got 178 pps throughput. This still equates to around a 75 percent decrease, which is still substantial. To see what it was like to experience a 75 percent decrease in throughput, we tried surfing to a website having a few graphics. With the microwave running, the pictures would come in painfully slowly. We also surfed around a bit to other pages, and sometimes the pages would freeze. After turning off the microwave oven, we cleared the browser cache and found no problems surfing the same web pages.

Cordless phones cause interference with WLANs. Today, a person can purchase cordless phones that operate in a variety of unlicensed frequency bands: 900 MHz, 2.4 GHz, and 5 GHz. A cordless phone will cause interference only with WLANs operating in the same frequency bands as the phone. For example, a 2.4-GHz cordless phone can interfere with WLANs operating in the 2.4-GHz band but not the 5-GHz band.

My consulting firm, Wireless-Nets, Ltd., has had an opportunity to do some Wi-Fi interference testing with several Plantronics 2.4-GHz cordless phones. We found that the cordless phones, when switched on (with or without a dial tone), always transmit a 10-MHz-wide signal in the 2.4-GHz ISM band, which is roughly 90 MHz wide. We could clearly see from a spectrum analyzer that turning on a second phone would produce another 10-MHz-wide signal in an unoccupied part of the band. Apparently, the phones search for the least congested area and tune their transmitters to that frequency. With a fairly clean spectrum, with no Wi-Fi or Bluetooth devices operating, we could turn on six of the phones, which filled approximately two thirds of the spectrum. Based on the way that the phones were operating, the use of cordless phones (at least the Plantronics model we tested) will reduce the capacity for supporting Wi-Fi signals. Because a Wi-Fi access point operating in the 2.4-GHz band uses one third of the spectrum, the operation of six phones would leave enough room for a single access point. If there is a need for operating nine phones in the same general area as an access point, then interference between the access point and the phones (the three using a frequency that overlaps with the access point) will occur. The result is distorted voice heard over the phone when talking to someone and a much higher frame retransmission rate at the access point. Keep in mind that varying cordless phone models operate differently, so it is worthwhile to test them if they will be used in conjunction with a WLAN.

The most common wireless technology, 802.11g (wireless-G), operates at a frequency of 2.4 gigahertz (GHz). Many wireless electronics such as cordless telephones, microwave ovens, baby monitors, and garage door openers use this same frequency. As a result, their signal noise could interfere with the connection between your device and router.To reduce noise, buy cordless telephones and other devices that use the 5.8 GHz or 900 megahertz (MHz) frequencies. Because 802.11n (wireless-N) operates at both 2.4 GHz and the less frequently used 5.0 GHz frequency, these higher GHz devices may cause less network interference.

Microwave ovens operate in the 2.4 GHz band, and typically create a mountain-like shape in the Density View. Most people use a microwave oven in exact time lengths like 1 minute bursts, which are easily measured in the Waterfall View. The amplitude levels of microwave oven leakage in the 2.4 GHz vary depending on their age, shielding, and distance from the spectrum analyzer.

One downside of the 2.4 GHz frequency is that it has become more and more crowded. This is partly because it provides fewer channels than the 5 GHz band. As a result, in addition to interference from other WiFi routers located nearby, your 2.4 GHz WiFi network can experience interference from many common household devices. These include microwave ovens, cordless phones, wireless speakers, Bluetooth devices and baby monitors. And when your network is experiencing interference from these nearby devices, your speed and overall performance suffer.

  • Factors that affect your wireless experienceProximity to wireless access points: the closer you are to a wireless access point, the more likely you are to receive a strong signal.

  • Total number of users and total amount of traffic: Wi-Fi is a shared medium, which results in many wireless devices competing for a set amount of available bandwidth. The number of users and amount of traffic on NDSU's wireless network peaks during regular operating hours (8 a.m. to 5 p.m., Monday through Friday). For this reason, IT recommends connecting to the wired network when transferring large data files or streaming long videos, particularly during peak traffic hours.

  • Sources of radio frequency interference: radio frequency interference involves the presence of unwanted radio signals that disrupt access to the wireless network. Potential sources of RF interference include cordless phones, Wi-Fi enabled printers, wireless cameras, Bluetooth devices, wireless game controllers, wireless audio headsets, and computer peripherals (e.g., wireless mice and keyboards). RF interference can also be caused by other devices, such as florescent lighting and microwave ovens.

  • Sources of passive wireless interference: passive wireless interference can be caused by some construction materials, furniture, and home decor items. These materials can absorb or obstruct a wireless signal.

  • Wireless InterferenceWireless access points, specifically 802.11b and 802.11g both use the shared 2.4GHz wireless band. Other devices that operate in this band can prevent Wi-Fi from working or severely degrade the service.Unauthorized Wireless Devices: one major interference source is unauthorized wireless devices, most commonly wireless routers. These devices can disrupt the service for neighboring wireless access points. They also pose a security risk and are in violation of acceptable use policy. The IT Division will detect and disable unauthorized wireless routers. Using a computer or other device to create an ad-hoc wireless network, where the device acts as a relay for other devices to connect to the Internet, is also against acceptable use policy. We recommend disabling this feature because both the host ad-hoc device and all connected devices will have a much slower connection.

  • Cordless Phones: cordless phones operate on many different frequencies. You can typically find out which frequency your phone uses by simply reading the labels. They include the following: 900MHz, 2.4GHz and 5.8GHz. A computer using Wi-Fi may have connection problems if anyone is using a 2.4GHz phone in the area.

  • Microwaves: microwave ovens can also cause interference with Wi-Fi devices. If a computer within 10 feet of an operating microwave is experiencing slow connection, consider relocating one of the devices.

  • Bluetooth: devices that are Bluetooth-capable, including laptops, smartphones, keyboards and mice, can also interfere with Wi-Fi access.

  • Construction materials, furniture and home decor items: items consisting of metal or plaster with embedded mesh (e.g., furniture, metal decor, lighting, appliances) cause very high levels of interference. Items consisting of paper or heavy fabric (e.g., books, draperies, posters) cause high levels of interference. Items consisting of glass (e.g., glass decor, windows) cause medium levels of interference. Items consisting of wood or sheetrock (e.g., walls, wood furniture) cause low levels of interference.

  • Tips for minimizing potential interferenceIf possible, avoid using devices that operate in the following frequency ranges used by 802.11:

  • 2.40 - 2.485 GHz

  • 5.18 - 5.6 GHz

  • 5.68 - 5.86 GHz

  • Use 5 GHz wireless options whenever possible. You will find this option for both 802.11a and 802.11n. Using this band will provide better performance by limiting the potential of interference as well as having more non-overlapping channels. (Note: Not all devices support 5 GHz. For assistance, contact the IT Help Desk.)

  • If wireless performance in your room or office is inconsistent or poor, consider whether other devices or construction materials in close proximity may be interfering with your wireless connection. Simply moving your wireless device to an alternative location in that space may provide better connectivity.

  • Turn off Wi-Fi on your cell phone if you are using cellular for your data connection.