Section I. INTERFERENCE
External interference consists of all external natural and manmade disturbances which interrupt or
interfere with the electrical or electronic properties of operation, maintenance, or testing, and which cause either
improper operation or indication, or diminished equipment performance.
a. Atmospheric interference is caused by the many thunderstorms that occur over the surface of the
earth. In ordinary communication equipment, this interference appears as noise, a constant background rumble
with loud crashes occurring at irregular intervals. The noise may not be heard at all times, but it is always present
in receivers and may be a source of an unidentifiable interference problem.
b. Lightning produces electromagnetic waves which are scattered in all directions. These waves are
received locally as overriding volume crashes. In addition, the waves can be transmitted to distant antennas
because these waves can be reflected and refracted from the ionosphere at such an angle as to be directed to the
a. Cosmic noise is a continuous noise received from other galaxies. This noise is probably caused by
magnetic storms resulting from the thermonuclear reactions continuously occurring on the suns of these distant
galaxies. This noise is not particularly directional because the transmitting galaxies completely surround our own
b. The noises received from within our own galaxy are called galactic noise and are normally directional
because they originate from definite traceable sources. Again, this is a type of noise that is comparatively
c. Noise received from the stars within our own galaxy is highly directional and normally possesses a
greater amplitude than cosmic interfering signals.
d. The noise received as a result of the thermonuclear reactions occurring on the sun is the greatest
source of noise existing outside the sphere of our own planet. During periods of sunspot activity, this highly
directional source will vary as the earth rotates, and maximum interference will result when the receiving antenna
is directed toward the sun. This solar noise has the greatest effect in the Arctic Zone and the least effect in the