Radio frequency interference is extraneous energy that impedes the reception of
signals. It can be caused by a radio emission from another transmitter at approximately
the same frequency. When we talk about the frequency that an AP radio operates on, we really
mean its “center frequency,” because both the transmitter and the receiver
operate within a band of frequencies that is several megahertz (MHz) wide.AP
transmitters will transmit strongest at frequencies very close to its center frequency,
with a decrease in signal strength as you move away from the center frequency.
Similarly, the wireless AP receiver will be most sensitive to frequencies
very close to its center frequency, with a decrease in sensitivity as you move away
from the center frequency. Note that the center frequency of the receiver can be
slightly different than the center frequency of the transmitter and things will still
seem to work okay, but because power decreases as you move out from the
center frequency, range will be reduced.
The width of this band of frequencies around the center frequency is a major
factor in determining the effects of radio interference. If your receiver encounters
a second signal that is too close to its center frequency and the two bandwidths
end up overlapping too much, interference will result.The closer the interfering
signal is to the receiver’s center frequency, the less power is needed to cause
interference. In the extreme case, if somebody turns on their microwave oven
and its emanations are on exactly the same frequency as yours, you may drop
down in speed even if the signal is very weak. Conversely, if something is operating
on a frequency that is quite far away from the center frequency of your
AP’s receiver, it can still interfere if its signal is strong enough.