(1) When one communications system interferes with another or when one unit in a system
interferes with other units in the same system, there is a condition of mutual interference.
(2) Mutual interference may appear in several forms, such as noise, crosstalk, and harmonic
interactions. Some of the common conditions that cause mutual interference are as follows:
(a) Transmitter fundamental radiation to receiver fundamental response.
(b) Transmitter spurious radiation to receiver fundamental response.
(c) Transmitter fundamental radiation to receiver spurious response.
(d) Transmitter spurious radiation to receiver spurious response.
(e) Receiver radiation to receiver fundamental response.
(f) RF arcing in transmitters.
(h) High voltage pulse interference.
(i) Improper frequency assignments.
(3) Spurious radiation refers to signals radiated from the transmitter on many frequencies
other than the fundamental or carrier frequency. While these spurious radiations are weaker than the
fundamental or carrier frequency, they may be strong enough to cause interference (noise) in nearby
receivers. This is true especially when a receiver is tuned to a frequency corresponding to one of the
spurious transmitter radiations.
(4) If these interference signals are strong enough, they may be amplified to the point where
they will render the desired signal unintelligible. It is possible for the local oscillator in a
superheterodyne-type receiver to radiate a signal which can cause interference. This is known as
receiver radiation.
(5) Mutual interference may originate from many local and distant sources. Frequency
relationships, geographical locations, faulty adjustment of equipment, improper operating techniques,
and weather conditions are factors contributing to mutual interference. Equipment and systems that are
potential generators of mutual interference include radar, radio, radio aids to navigation, and telephones.
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