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RF Basics

When troubleshooting your wireless network, it is helpful to understand how wireless signals, or RF (Radio Frequencies), travel through your home or office. Similar to other radio devices such as cordless phones or walkie-talkies, signal quality and strength decreases as the distance between the transmitter and receiver (wireless router and computer) increases. Additionally, obstacles such as walls, floors, and furniture can block or reduce the wireless signal.

To better understand how these signals travel, imagine your AP as a tiny light—a naked light bulb (to simulate an omni-directional, or dipole antenna). This analogy works well in an "open field" environment where there is a clear line of sight between the bulb (your Access Point or wireless Router) and your eye (your wireless-equipped laptop), but requires a little bit of tweaking for an indoor environment.

So also picture your home's walls, ceilings, and furniture not as solid objects, but more like translucent panels or objects with varying opacity. The more panels or objects between the bulb and your eye, the more difficult it will be to see the light.

The antennas used on your wireless networking devices play a major role in how the signal propagates, or travels. Most wireless networking gear (wireless routers and adapters) come with omni-directional antennas, which means the signal is transmitted with equal strength in all directions. Other types of antennas include directional antennas with varying "gains" or amplification factors and high-gain omni-directional antennas.

Going back to the light bulb example, you could think of putting a curved reflector behind the naked light bulb as similar to attaching a directional antenna to your AP. The reflector wouldn't change the amount of light (radio power from the AP) being transmitted, but instead concentrate the light in a desired direction.

We will cover more on antennas and their uses later in this series.

RF Interference

In addition to interference caused by other wireless networks on the same channel or from overlapping channels, other radio devices can interfere with wireless networks. The following devices that use (or bleed onto) the 2.4 GHz frequency band are common culprits:

  • Cordless phones
  • Baby monitors
  • Kitchen microwaves
  • Wireless speakers and headphones
  • Bluetooth devices

NOTE!Note: We are focusing primarily on the 2.4GHz band, which is used by 802.11b, g and draft n products. But similar interference problems can occur with 802.11a and draft 11n products that use the 5 GHz frequency band.

However, since each channel in the 5 GHz band uses non-overlapping frequencies, and 5 GHz WLAN gear is much less commonly used, interference is typically less of a problem. But it is only a matter of time until the 5 GHz band suffers from the same congestion as the 2.4 GHz band.

The effect of the interference by devices like these varies. It can be minimal, causing only a slight drop in performance and speed. However it is not uncommon for the interference to completely drown out the wireless signals, stopping your Wi-Fi network in its tracks.

An interesting round of tests performed by the Farpoint Group, released in a paper last January titled The Effects of Interference on General WLAN Traffic, shows how bad interference can be to your wireless network. They found that a microwave oven caused more than 62% reduction of throughput (the amount of data transferred) on their wireless test network compared to measurements without the intentional interference. Additionally the study found a 89% reduction from a neighboring wireless LAN and almost a 20% reduction in throughput from a Bluetooth headset. But the most damaging interferer was a cordless phone, causing "complete obliteration (100% degradation) of a Wi-Fi link." (my cordless phone does this too!)

Revisiting the light bulb example, you could imagine these interfering devices as "light" sources as well. Depending upon the number, location, and power of these other light sources (2.4GHz cordless phones or microwaves) it may make it difficult, or even impossible, to differentiate the light in the area from the lamp bulb (your AP) and the interfering sources.

We will cover more on how to address and overcome RF interference in another part of this series.

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