About

News

Analysis of LNB common anomalies

Author:小闻 ComeFrom:闻颂智能科技有限公司 Date:2019-11-4 16:33:49 Hits:178

"At present, LNB has been localized, and there are many manufacturers in China, but there is no uniform standard, and the quality is uneven. Some newly purchased c-heads are used according to the conventional method, and c-heads do not necessarily work normally, which makes digital machines show various abnormal phenomena. Strictly speaking, although some abnormal phenomena can not be regarded as faults, they are just a flaw in the design and debugging process of C head, but sometimes they will bring some inconvenience to the use. Without prior knowledge, the installation and debugging of antenna feeder system may take a detour. "


1. "Local vibration drift" phenomenon


The main performance is: input the standard downlink frequency published by the program operator in the digital machine, no signal can be received, or although the signal can be received, the displayed value of "signal quality" is seriously low, and repeated adjustment of the antenna system can not greatly improve the "signal quality". Sometimes when the blind scanning function is enabled, the program can be searched, but the searched downlink frequency value and standard The downlink frequency of is obviously inconsistent. The C head with local frequency drift can be corrected by adjusting the local frequency adjusting screw of C head, and can also be processed by increasing or decreasing the local frequency or the down frequency in program parameters.


2. "Anti polarization" phenomenon


Most of the polarizing pins receiving the horizontal polarization signal of the dual polarization C head are parallel to the isolating pin, and the vertical polarizing pin is vertical to the isolating pin. When a C head is installed, the polarizing angle of the C head can be roughly set according to the arrangement of the receiving satellites and polarizing pins. Some c-head horizontal and vertical polarizers are arranged exactly opposite to most c-head. If c-head is installed according to the conventional use method, the received signal strength will be reduced, or even the signal cannot be received. When using this kind of c-head, it is only necessary to change the installation mode of c-head or modify the polarization mode in the digital machine, so that the polarization mode of the digital machine is consistent with the actual polarization pin in the c-head.


3. "Only horizontal polarization signal can be received" phenomenon


This kind of fault is common in the generation and switching circuit of polarization voltage of digital machine, so it should be noted that it is different from the fault of digital machine. Connect the power supply of the digital machine, operate the polarization mode of the digital machine to switch between horizontal and vertical polarization, measure the normal 13 / 18V polarization voltage at the intermediate frequency signal input terminal of the digital machine, indicating that the generation and switching circuit of the polarization voltage of the digital machine are normal, and the C head should be in fault.


Two high frequency amplifying circuits inside the C head respectively amplify the horizontal and vertical polarizing satellite signals input by two mutually perpendicular polarizers. The two high frequency amplifying circuits with different polarizations do not work at the same time and must be switched by the polarization switching circuit. Generally, the voltage at the switching point of the horizontal and vertical polarizations of the high frequency head is 14.5V, when the output polarization voltage of the digital machine is greater than 1 4.5V (e.g. 18V), the electronic polarization switch inside the high frequency head is switched to the horizontal polarization signal high amplifier circuit, and the digital machine receives the horizontal polarization signal; when the digital output polarization voltage is less than 14.5V (e.g. 13V), the electronic polarization switch inside the high frequency head is switched to the vertical polarization signal high amplifier circuit, and the digital machine receives the vertical polarization signal.


The reason why the digital machine can not receive the vertical polarization signal is that the switching voltage value of the electronic polarization switch in the high frequency head is set too low, that is, the voltage setting value of the polarization switching point is lower than the normal 14.5V, the horizontal and vertical polarization voltage output by the digital machine are higher than the actual voltage setting value of the polarization switching switching point of the high frequency head, and the high frequency head only works In the state of receiving horizontal polarization mode, the digital machine can only receive horizontal polarization signal.


The processing method is: in the power supply line of the high frequency head, the forward series rectifier diodes are connected, and the series diodes make the horizontal and vertical polarization voltage of the output of the digital machine drop in the same proportion. Because the horizontal polarization voltage is high, the slightly lower the voltage will not affect the reception of the horizontal polarization signal, and when the vertical polarization voltage drops below the set value of the actual polarization switching point voltage, it can be Vertical polarization signal received. The number of series connected rectifier diodes shall be determined by the specific test conditions.
Next:How to protect LNB effectively?
Copyright © 2018 All rights reserved:suzhou waython intelligent technology co., LTD.   SU ICP:18028043-1  Technical support:zhuocheng network technology