In Physics, What Is Interference?

Physics, instrument and other external factors affect the determination. Electromagnetic oscillations that prevent radio equipment from properly receiving signals. Mainly caused by electrical devices near the receiving equipment. Astronomical and meteorological changes such as sunlight and magnetic storms can also cause interference.

Physics, instrument and other external factors affect the determination. Electromagnetic oscillations that prevent radio equipment from properly receiving signals. Mainly caused by electrical devices near the receiving equipment. Astronomical and meteorological changes such as sunlight and magnetic storms can also cause interference.

Chinese name

interference

Foreign name

interference

Applied discipline

Physics, Communication

Interference noise

Atmospheric noise Electromagnetic radiation generated by thunderstorms in nature, also known as celestial interference (or lightning radiation). It is a non-stationary random process. Atmospheric noise anywhere on the earth is the superposition of lightning radiation in this area and lightning radiation in other areas, so its amplitude characteristics can generally use large non-Gaussian narrow spike pulses (lightning radiation generated nearby) and A series of small-amplitude Gaussian spike pulses (produced in remote areas) are superimposed on each other to describe. The degree of interference from antennas is related to the distance to the center of lightning. Lightning activity in various places is related to its geographical location. The report of the International Radio Advisory Committee (CCIR.322) gives the global distribution of this type of interference, that is, there are more mid- and low-latitude areas and less in high-latitude areas. The main lightning activity centers around the world are located near the equator in Africa, the Americas and Asia. Generally, summer is more strong and winter is less and weaker, and more often occurs in the evening.

From the perspective of frequency domain characteristics, the radiation spectrum in the near region of lightning is relatively wide, up to 5 kHz; in the far region, only the low frequency part is left due to the propagation attenuation, and two maximum values appear. Below 1kHz and between 7 ~ 20kHz, the minimum value is about 4kHz.

The interference of atmospheric noise on radio communications is mainly in the bands below the low frequency. However, thunder and lightning in this region, especially in tropical regions where thunder and lightning are concentrated, will also have a serious impact on short and medium waves. But the impact on 30MHz and above gradually weakened.

Atmospheric noise level is not only related to region, season, day and night, time and weather conditions, but also closely related to frequency, which generally decreases with increasing frequency. However, since the absorption of radio waves by the ionosphere during the day decreases with increasing frequency, the level of atmospheric noise in the short-wave band increases with increasing frequency, and the absorption of the ionosphere at night is small, and the atmospheric noise is almost independent of frequency.

Atmospheric noise is usually expressed as a statistical value of the noise level per unit bandwidth. Atmospheric noise is external noise. It has large and fast fluctuations, but slow fluctuations are not obvious. If the noise power is averaged over a few minutes, it will hardly change over a given hour. In addition to near-sunrise, sunset or local thunderstorm activity, there are few changes of more than ± 2dB.

Interference electromagnetic interference

Interference electromagnetic interference source

There are two kinds of electromagnetic interference sources: natural and man-made. Natural interference sources mainly include various phenomena that occur in the atmosphere, such as noise caused by lightning, snow, rain, hail, and sandstorms. Natural interference sources also include cosmic noise from the sun and outer space, such as solar noise, interstellar noise, and galactic noise. There are various sources of artificial interference, such as various signal transmitters, oscillators, motors, switches, relays, neon lights, fluorescent lights, engine ignition systems, electric bells, heaters, arc welding machines, high-speed logic circuits, gate circuits, Thyristor inverter, gas rectifier, corona discharge, various industrial, scientific and medical high-frequency equipment, urban noise, noise caused by electric railways, and nuclear electromagnetic pulses generated by nuclear explosions.

Disturbance of electromagnetic interference

There are two types of electromagnetic interference propagation: conducted interference and radiated interference. Interference propagating along a conductor is called conducted interference, and its propagation modes are electrical coupling, magnetic coupling, and electromagnetic coupling. Electromagnetic interference that is transmitted in the form of electromagnetic waves through space is called radiated interference, and its propagation methods include near-field induction coupling and far-field radiation coupling. In addition, conducted interference and radiated interference may also coexist, thereby forming a composite interference.