LEARNING EVENT 4: SEASONAL
1. In any given area, the change from spring to summer or from any season to another will result in changes in
both atmospheric noises and interference caused by solar radiation.
2. The atmospheric seasonal changes are primarily due to changes in temperature and humidity. As the
temperature or humidity gradually increases, the interfering noises will increase in direct proportion.
3. During the night, when the portion of the Earth in which you are located is not facing the sun, you will not
receive the same amplitude of solar noises. The electron bands in the upper atmosphere will lift and be a
greater distance from the Earth. Interfering noise from the sun will diminish because the sun is not primarily
directed toward the night side of the Earth.
LEARNING EVENT 5: TERRESTRIAL
1. Interference caused by geographical conditions is associated with the metallic or chemical content of the
Earth surrounding the location of the ground station.
2. In specific areas or points, the Earth may have a high metallic content which will effectively introduce a
magnetic field. This magnetic field may be coupled into the transmitting or receiving equipment by way of the
desired signal, it may couple the desired signal to ground, or it may reduce the power of the signal. This
metallic interference normally remains constant.
3. The interfering noise signals that accompany volcanic eruptions are normally effective only in the local
region. The noise is caused by particles that have been electrostatically charged by the movement of gas and
lava up through the Earth's surface, by the heat of the lava, and by the precipitation of dust or smoke particles.
LEARNING EVENT 6: FADING
1. Signal fading is not a noise-producing type of interference. It is classed as interference only because it
makes reception of a desired signal difficult and thus interferes with the efficiency and accuracy of electrical or
2. Fading, or fluctuation, of a desired signal may be due to disturbances in the medium through which the
signal is propagated. The tropospheric, stratospheric, and ionospheric layers above the Earth's surface
constitute the medium. An incoming signal may lose or gain strength; either condition is called fading.
However, it is only when the normal signal strength weakens that reception becomes difficult. The signal
strength may drop