reasons for the low quality of satellite TV signals
The deterioration of satellite TV signal quality is manifested in the increase of mosaics, pauses, loss of receiver locks, and even crashes,the first feeling that give people is to suspect that there is a problem with the TV station or satellite – reason is that the reduction of the power of the TV signal it transmits.
In fact, on the contrary, it is rare in practice that the signal power decreases due to the satellite TV uplink transmitting station or satellite, so that the reception quality is reduced, and it is often caused by its own reception. The entire receiving chain has many loop symbols, and many situations will cause the signal quality to decline. Therefore, when problems occur, they need to be considered and analyzed comprehensively. It cannot be simply attributed to the TV uplink station or satellite.
The following will comprehensively analyze the reasons for the degradation of signal quality for your reference.
personal reasons
It is very simple, its own reason is the failure caused by its own human or equipment reasons.
human reasons
whether the selected antenna is too small or of poor quality
The selection of the antenna is very important. The principle should be: the antenna with good quality, high precision and accurate focus must be selected. As an individual receive, you can’t blindly pursue smaller-sized antennas, but you can’t superstitute large-diameter antennas either. The 1m Ku single-receiver antenna with insufficient accuracy and inaccurate focus may not be as strong as the signal received by the 0.75m antenna. Antennas with smaller diameters are easy to install and cost-effective, but there is a slight “turbulence”, such as bad weather, signal interference, etc., the mosaic phenomenon will appear immediately. The selection of the antenna aperture is too large, and the receiving margin is large,In order to improve the usability, it is necessary for professional reception, but as an individual reception, it will inevitably cause unnecessary expenses.
Satellite companies (or TV stations) generally give a recommended antenna diameter for a different area according to the difference in the field strength of satellite coverage and the coordination of neighboring satellites. It has taken into account many interference factors and set aside a certain reception margin, so when you select antenn, the recommended antenna diameter should be used as much as possible or a little smaller (the one recommended by satellite companies is generally conservative). If there is no recommendation, the aperture of the individual receiving antenna only needs to be larger than the receiving threshold of the signal when it is sunny.
unreasonable antenna location and wiring
Improper site selection of the antenna, such as the location near the transmitting station, the air outlet, the place easy to be touched by people or animals or the place with unstable foundation, and the proximity to strong electricity and possible interference sources around the antenna when wiring are all the reasons for the deterioration of the received signal.
In rainy and snowy weather, the water in the antenna area is not treated in time
equipment reasons
the antenna is not aimed at the position of the satellite
First consider whether there is a strong wind that may blow the antenna off, such as the poor quality of the antenna and the possibility of antenna deformation, so that the alignment of the satellite is not accurate; or the antenna is hit by foreign objects; or the antenna is mechanically deformed due to years of work.
LNB local oscillator L. O. (Locaf oscillator) excessive frequency drift is a common cause of failure affecting normal viewing.
There are many indicators to measure LNB, mainly including: local oscillator stability, noise temperature, gain and phase noise. The more problems occured with the LNB is that the local oscillator frequency drift is too large. Between ordinary home-grade LNB and professional-grade LNB,the difference is mainly reflected in the stability of the local oscillator frequency. The indicators of noise temperature, gain and phase noise are also very important.
The frequency stability of the LNB is determined by the frequency stability of its local oscillator. Home LNBs generally do not have Phase Locked Loop PLL (Phase Locked Loop), while professional-grade LNBs basically have PLLs. Even if they do not have PLLs, they will use a high-stability dielectric resonator DRO (Dielectric Resonator Oscillator).
The quality of ordinary household-grade LNB is difficult to guarantee, and the working performance is unstable, which is mainly reflected in the poor thermal stability of the local oscillator frequency and the large drift affected by the ambient temperature.
For the LNB whose local oscillator frequency drift is not serious, if there is no spectrum analyzer to test the frequency deviation, the solution is: when the TV carrier loses lock, increase or decrease the frequency that should be set by a value, such as ±500KHZ or ± 1MHZ, keep trying to add and subtract until stable ratings. Then continuously add and subtract the carrier frequency to find the upper/lower limit frequency when the receiver loses lock, and set it as the actual receiving frequency after taking it. For the LNB with serious local oscillator frequency drift, it can only be replaced.
cables and connectors
Under normal circumstances, as long as the quality of cables and connectors is good, the possibility of problems is small, but it cannot be completely ruled out. So when problems arise, consider:
1.Whether the cable has been moved;
2.Rewired;
3.Whether the quality of the cable connectors is not high, resulting in loose joints, poor contact or short-circuit of the core;
4.Whether the waterproof is not handled well, whether it has entered water, etc.
If business as usual, there is little doubt about this issue.
Generally, professional receiving antenna feeds are equipped with plastic protective covers to prevent cable connectors and feeds from entering water and foreign objects. For household reception, you can find a plastic beverage bottle to cover it.
the receiver
The receiver must be selected for stable and reliable operation and good quality. If there is a problem with its internal video processing decoder, it will cause mosaic phenomenon. If the video decoder in the receiver does not work properly due to poor ventilation and heat dissipation, pay attention to the heat dissipation of the receiver; if the image appears mosaic due to software and hardware design, you need to try another receiver with better quality. It can be verified; in the case of network sharing decoding, the network speed and the processing speed of the shared server are the factors that affect the image quality.
various diseqc switches
When you need to receive multiple satellites or multiple households, you need to use a switch, such as: 0/12V, 13/18V voltage switch; 0/22KHz pulse switch, DiSEqC switch, various power dividers,etc.. If the quality of these devices is poor, the signal attenuation loss will be relatively large, which will directly affect the viewing quality. Therefore, it is also very important to choose a good switch.
It should be noted that if the length of the cable used is not enough, when connecting the cable in series, it should be noted that the impedance of the cable, joint and connector should be matched, otherwise reflection will occur and the standing wave ratio will become larger. The TV carrier will appear jagged, and the frequency response is very poor, which also affects the reception quality.
external reasons
Since it is not its own reasons, it must be external reasons, and there are many factors.
uplink station
1.Uplink devices such as power amplifiers and modulators are switched to backup devices due to failures, but the power is not calibrated, and the uplink power drops.
2.The uplink station is switched from station A to station B, the power is not calibrated, and the uplink power decreases;
3.The automatic tracking of the antenna is not accurate, or the antenna needs to re-track the satellite;
4.The TV carrier has overpower usage, which is corrected by the satellite company, so the uplink power is reduced.
5.There is interference;
For example, if there are intermediate frequency crosstalk, intermodulation interference, and forwarding interference in the uplink system, the really useful signal will be occupied by useless interference noise, and the carrier-to-noise ratio will be swish. Although the signal is strong enough, the quality is not high, and the signal will go to the satellite with interference.
satellite
1.There is interference, such as reverse polarization interference, adjacent channel interference, adjacent satellite interference, etc.; co-channel interference, when there are 3 interfering carriers in the frequency band used by normal TV carriers, which affects the quality of normal signals.
2.Satellite attitude, abnormal orbit, transponder gain jump, etc.
The failure rate curve of a satellite is similar to a “U” shape (the so-called “bathtub curve”), that is, the risk of the satellite is relatively high in the first year after being put into operation and at the end of its life, while the risk in the mid-term operation is relatively small, and the reliability is high. Failure is unlikely, but not impossible.
3.Solar transit interruption
The solar transit is a common astronomical phenomenon that occurs regularly around the spring and autumn equinoxes every year. At this time, the satellite is between the sun and the earth, and at the same time,the antenna of the earth station may be aimed at the sun too,when antenna aim at the satellite,at this time, the strong solar noise makes the communication impossible to carry out. The noise was raised by nearly 10dB when the solar transit occurred. This interruption occurs twice a year, each lasting about 6 days. The time and length of each day are related to the diameter of the earth station antenna and the working frequency band, and the signal is interrupted for about ten minutes.
If the satellite is to the east of the receiving station, the outage occurs in the morning, and vice versa, the outage occurs in the afternoon. For the geostationary satellite communication system, the interruption of solar transit is predictable, but generally unavoidable. For very important receiving stations, generally adopt the method of increasing the antenna aperture to reduce the interruption time, or adopt the method of remote station backup to avoid signal interruption.
space
1.Precipitation attenuation, especially the Ku frequency band, has a greater impact.
The uplink ground station generally has the uplink power automatic control system UPC, and the satellite also has the automatic level control system ALC to deal with the rain attenuation phenomenon. When there is rain, snow or dense fog at the uplink station, for general precipitation, the ground station or satellite can compensate in time. However, if the precipitation is heavy, the compensation has no effect. For example, in heavy rain, the signal will be completely attenuated.
2.Ionospheric scintillation and atmospheric scintillation – small probability events, generally not considered
3.Sunspot eruption – a small probability event, generally not considered
other objective factors
Whether there are new buildings or plants in front of the antenna, whether new high-voltage lines are erected, new transmitting stations, whether the radio and television department has turned on the interference equipment, etc., these are the reasons for the deterioration of signal quality. If it is determined to be the above reason, it can only be solved by moving the antenna position, increasing the antenna aperture, or trying to receive other satellite signals
analysis summary
Large rain attenuation, antenna offset, LNB frequency offset and local interference are the common fault reasons for the degradation of individual reception; while the relative problems of uplink stations are large rain attenuation and interference.
Due to the high availability requirements of the radio and television industry in my country, satellite companies and uplink stations have a mature and complete monitoring and backup system for satellite and TV carriers, as well as comprehensive emergency response plans. Therefore, when a problem occurs, as an individual user, you should focus on checking your own reasons first. At the same time, don’t tamper with the device blindly, such as aim at the satellite, changing lines, etc., if you can confirm with other nearby users, it is best. After the self-check is correct, it is suspected that there may be a problem with the uplink station or satellite, report the situation to it and solve the problem under its guidance and suggestions. You can also go to some satellite TV forums to exchange and summarize experience, so that you can better deal with it in the future.