INTERFERENCE

Interference in the world of wireless means any unwanted signal that interferes with receiving the desired signal or hurts the quality of its reception.  Interference becomes a complex subject since most wireless products do not simply transmit on a single frequency, but also generate some unwanted frequency products at lower power levels that can also do harm and create interference.  These unwanted frequencies often are at multiples (times 2, times 3, and so on) of the fundamental transmit frequency.

On example of this type of interference is with CB (citizens band) radio in the US.  Some CB channels were approximately at 27 MHz in frequency.  However, these products also would have some frequencies - though lower in power - at unwanted frequencies that were multiples of the basic transmit frequency.  A CB radio operating at 27MHz also has some energy at twice at frequency - at 54 MHz.  And this frequency at times in the US can be seen to interfere with a lower television channel if the CB radio is operated nearby.  While this example has been seen in practice, this is certainly not the only case of interference, just one example of it.

Some products such as digital products such as computers can generate multiple interference frequencies.  However, often this interference is very low in power level and often does not interfere with radio products - even if nearby.  Of greater concern for engineers are digital circuits operating near radio circuits within the same product.  A product of course can also interfere with itself and engineers must ensure that that does not happen for each consumer product.