Just as the signals from two antennas will mix intentionally to increase transmission power and form beams, signals from other transmissions and environmental noise will also mix with transmitted signals, degrading the signal’s quality.

When other signals or environmental noise mix with a signal, degrading its quality, this is called interference.

Noise will have the largest impact when it is either close to the same frequency or is very powerful. More powerful signals might include an electrical wire, an amateur radio set, fluorescent lights, some kinds of LED bulbs, a lightning storm, an automobile engine, a television set, and a generator. Anything using high-power electronics to accomplish a task can emit signals, interfering with wireless data transmission. Wi-Fi, described in the next section, is particularly susceptible to this kind of interference because it operates in an unlicensed frequency range shared by many other kinds of devices.

Microwave ovens are one classic source of interference for Wi-Fi systems because they operate in the same 2.4 GHz frequency range as one band of Wi-Fi. Other devices operating in the 2.4 GHz band include baby monitors, handheld radios, and Bluetooth. Find more information at: https://www.acedexam.com/500-301-ccs-cisco-cloud-collaboration-solutions/

Electromagnetic waves also expend more power when passing through materials other than air. For instance:
• A brick or concrete wall will allow around 20% of a Wi-Fi signal to pass through.
• A sheet of metal will allow around 30% of a Wi-Fi signal through.
• An empty metal rack will allow around 50% of a Wi-Fi signal through.
• A clear window, sheet of drywall, or wooden door will allow around 70% of a Wi-Fi signal through.

These numbers are approximate; a refrigerator, washing machine, or other large appliance largely constructed of metal can block close to 100% of a Wi-Fi signal.

Bandwidth and Signal Strength

Bandwidth is often used to denote the maximum data-carrying capacity of a link, whether wired or wireless. The word is taken from the width of the frequency band the link can use. Figure 8-6 shows a simple example of the concept of bandwidth.

Figure 8-6 Bandwidth

In Figure 8-6, a 0 is represented by a 150 Hz signal, and a 1 is represented by a 100 Hz signal. The average of these two frequencies is 125 Hz, so we can call 125 Hz our carrier or center frequency. For a radio to receive this signal, the receiver would need to be tuned to a center frequency of 125 Hz and have a window of 50 Hz (so it can receive any signal 25 Hz above or below the center frequency).

The bandwidth of this signal is 50 Hz—the maximum frequency subtracted from the minimum frequency. To see how a wider bandwidth would help add more data in each timeframe, imagine if you could use four frequencies rather than two—but there still must be 25 Hz between the frequency representing each symbol—in this case a pair of binary digits. You might have something like this:
• 75 Hz represents 00
• 100 Hz represents 01
• 125 Hz represents 10
• 150 Hz represents 11

Now, you could transmit data twice as fast in the same timeframe, but you need 75 Hz of bandwidth (subtract 75 from 150) rather than 50 Hz.

Modern radio systems can send multiple bits of data in each wavelength using more complex modulation, but these systems require much wider bands, or channels, of radio frequencies.

For instance, channel 1 of the 2.4 GHz range of Wi-Fi frequencies is from 2401–2423 MHz, with a center frequency of 2412 MHz. The bandwidth of this channel, from a radio frequency perspective, is 22 MHz. Since a single radio signal with a bandwidth of 22 MHz can carry a maximum of 11 Mb/s, this is the specified bandwidth of the link.

However, to reach the optimal data rate, the signal must be strong, and interference must be low. Lower-powered and “dirty” signals cannot carry as many bits of data per wavelength. As signal strength decreases, or interference increases, the data rate decreases.