Flutter

Note: Examples of flutter are;

• rapid variations in received signal levels, such as variations that may be caused by atmospheric disturbances, antenna movements in a high wind, or interaction with other signals,
• in radio propagation, a phenomenon in which nearly all radio signals that are usually reflected by ionospheric layers in or above the E-region experience partial or complete absorption,
• in radio transmission, rapidly changing signal levels, together with variable multipath time delays, caused by reflection and possible partial absorption of the signal by aircraft flying through the radio beam[?] or common scatter volume,
• the variation in the transmission characteristics of a loaded telephone circuit caused by the action of telegraph direct currents on the loading coils,
• in recording and reproducing equipment, the deviation of frequency caused by irregular mechanical motion, e.g., that of capstan angular velocity in a tape transport mechanism, during operation.

Source: from Federal Standard 1037C and from MIL-STD-188