How does the weather affect the satellite TV signal?

1. The influence of rainy and foggy weather on satellite signals required for satellite TV installation.

Satellites are greatly influenced by rain, fog, clouds, snow and frost, because when electromagnetic waves propagate in space, some energy is absorbed or scattered by rain, fog, clouds, snow and frost, resulting in losses. The loss is related to the frequency of radio waves, the path they pass, the size of rain and snow, the concentration of clouds and other factors.

The attenuation of signal propagation in rain caused by the absorption and scattering of raindrops is called rain attenuation for short. In the frequency band above 3GHz, with the increase of frequency, the rain attenuation increases. Below 10GHz band, the influence of weather above moderate rain (rainfall of 4mm/h) must be considered; In millimeter wave band, the rainfall attenuation above moderate rain is quite serious. In the case of moderate rain, every 10km of the path length of radio waves passing through the rain area, the attenuation of C-band downlink signal is about 0.4dB. In the case of rainstorm (rainfall 100mm/h), although the loss intensity per kilometer is relatively large, the rain area is generally less than 2km. For the downlink signal of C-band, the attenuation per kilometer is 0.2dB, and the total attenuation value is about 0.4dB. According to the data provided by ITU, the ku-band signal is attenuated 1~ 10dB per kilometer during rainstorm or rainstorm.

Rain will also produce rain noise, which is equivalent to antenna thermal noise when converted to the input end of receiving antenna. Rainfall noise has a great influence on the carrier-to-noise ratio of the received signal, and the degree of influence is related to attenuation and antenna structure. According to the calculation, the noise temperature increases about 6.7k for every attenuation of 0. 1dB. Generally speaking, the higher the elevation angle of the antenna, the less the influence of rain noise, because the propagation path of electromagnetic waves in the rain is shorter and the attenuation is smaller.

2. The influence of solar eclipse and transit on satellite signal of satellite TV.

In addition to orbiting the earth, geostationary satellites also orbit the sun with the earth. Every year, during the 23 days around the vernal equinox (February1March) and the autumnal equinox (September 23rd), every day, when the satellite's sub-star point (referring to the intersection point between the satellite and the geocentric line and the earth's surface) enters around midnight local time.

The satellite, the earth and the sun are in a straight line. At this time, the earth blocked the sunlight and the satellite was in the shadow area of the earth. This astronomical phenomenon is called stellar eclipse, as shown in figure 1- 12.

An eclipse lasts 45 days at a time, which is 90 days. In addition, during the vernal equinox and autumnal equinox, the solar eclipse lasts the longest, 72 minutes. During the solar eclipse, the solar cells on the satellite can't work normally, and the energy needed for the whole satellite TV installation is provided by the on-board batteries. Through the design of the fixed position of the satellite in orbit, the communication business in the service area will be eclipsed in the shortest time to reduce the load of the battery.

The interruption of the transit of the sun occurs a few days before and after the vernal equinox and autumnal equinox every year. For a period of time before and after the point below the geostationary satellite enters the local noon, the satellite is between the sun and the earth, and the sun, the satellite and the earth are in the same straight line. This astronomical phenomenon is called the transit of the sun. When the sun transits, the antenna of the ground station may be aimed at the sun at the same time as the satellite, so a lot of solar noise will enter the ground receiving equipment, which will lead to signal interruption in serious cases. This phenomenon is called the interruption of solar transit. The main influence of the solar eclipse is to increase the noise temperature of the downlink transmission line, thus reducing the quality factor of the TV signal at the ground station (expressed by the ratio of the receiving antenna gain G to the system noise temperature T, in dB/k), and even interrupting the satellite signal. This phenomenon can last for several days at the vernal equinox and autumnal equinox every year, lasting for about a few minutes every day. The duration of the eclipse is related to the latitude of the ground station and the aperture of the antenna. The influence of solar eclipse interruption is generally inevitable, unless two different satellites are interrupted by solar eclipse, and the antenna of the ground receiving station is switched to receive the signal of the other satellite before the solar eclipse interruption.