Harmonics

 
Harmonics occur when signals are produced at two or three times the station’s
operating frequency in addition to the desired signals (see Figure 4.8). If the harmonics
fall on another locally used frequency, such as an AP channel, they are
likely to cause interference. Figure 1.11 shows how a signal from a radio device
may interfere with an AP set to channel 1.
These undesired transmissions occur at multiples of the original frequency. In
the example, harmonics of Device A, which is transmitting at 804 MHz, may
occur at 1.608 MHz (frequency × 2) or 2.412 MHz (frequency × 3). In addition,
Device A’s second harmonic is reduced in power by roughly half of the originating
signal’s power.The third harmonic’s power is roughly half of the second
harmonic and so on. As you can see in Figure 1.11, the harmonic frequencies of Device A could
present a potential problem in a wireless design. Although Device A’s second harmonic
does not interfere with the AP’s frequency channel, the third harmonic,
although weaker in strength, can affect the transmission and reception for the
channel 1 AP.