"At present, the high-frequency head has been localized. There are many manufacturers in China, but there is no uniform standard, and the quality is also uneven. Some new C-heads are used according to the conventional method. The C-head does not necessarily work normally. The digital machine exhibits various abnormal phenomena. Strictly speaking, although some abnormal phenomena cannot be counted as faults, they are only a flaw in the design and debugging process of the C-head, but sometimes it brings some inconvenience to the use. Without knowing it, the installation and commissioning of the antenna feeder system may be detoured."
1. "Local oscillator drift" phenomenonThe main performance is: input the standard downlink frequency announced by the program operator in the digital machine, and the signal is not received, or although the signal can be received, the displayed "signal quality" value is seriously low, and the repeated adjustment of the antenna feeder system cannot The “signal quality†is greatly improved. Sometimes when the blind scan function is enabled, the program can be searched, but the searched downlink frequency value is obviously inconsistent with the standard downlink frequency. The C-head of the local oscillator frequency drift can be corrected by adjusting the local oscillator adjustment screw of the C-head, or by increasing or decreasing the local oscillator frequency or the downlink frequency in the program parameters.
2. "Reverse polarization" phenomenonMost polarized pins of the double-polarized C-head receiving horizontally polarized signals are parallel to the isolating pins. The vertically polarized pins are perpendicular to the isolating pins. When a C-head is installed, it can directly receive the satellite and the pole according to the The arrangement of the needles is generally set to the C head polarization angle. Some C-head horizontal and vertical polarization pin arrangements are exactly the opposite of most C-heads. If the C-head is installed according to the conventional method of use, the received signal strength will be reduced or even not received. When using such a C-head, simply change the way the C-head is installed, or modify the polarization mode in the digital machine so that the polarization of the digital camera matches the polarized pin actually acting in the C-head.
3. "Can only receive horizontally polarized signals" phenomenonSuch faults are common in digital machine polarization voltage generation and switching circuits, so care should be taken to distinguish them from digital machine faults. Turn on the digital machine power supply, operate the digital machine polarization mode to switch between horizontal and vertical polarization, and measure the normal 13/18V polarization voltage at the digital machine IF signal input terminal, indicating the digital machine polarization voltage generation and switching circuit Normal, there should be a fault in the C head. In the C head, two high-frequency amplifier circuits respectively perform low-noise amplification on the horizontal and vertical polarization satellite signals input by two mutually perpendicular polarization pins. The two high-polarization circuits with different polarizations do not work at the same time. The polarization switching circuit performs switching. Generally, the horizontal and vertical polarization switching point voltage of the tuner is 14.5V. When the digital output polarization voltage is greater than 14.5V (eg, 18V), the internal electronic polarization switch of the tuner is used. Switch to the horizontally polarized signal high-discharge circuit, the digital machine receives the horizontally polarized signal; when the digital output polarization voltage is less than 14.5V (such as: 13V), the internal electronic polarization switch of the high-frequency head switches to the vertical polarization signal high-discharge circuit The digital machine receives the vertically polarized signal. Setting the digital machine to receive the vertical polarization signal and actually failing to receive the polarization mode signal is because the switching voltage value of the electronic polarization switching switch in the high frequency head is set too low, that is, the polarization switching point voltage setting value is lower than The usual 14.5V, the horizontal and vertical polarization voltage of the digital machine output exceeds the actual polarization switching point voltage setting value of the high frequency head. The high frequency head only works in the state of receiving the horizontal polarization mode, which is represented by the digital machine only. Can receive horizontally polarized signals. The processing method is: forwardly connecting the rectifier diodes in the power supply line of the high frequency head, and the diodes connected in series cause the horizontal and vertical polarization voltages of the digital machine output to decrease in proportion, because the horizontal polarization voltage is high, and the voltage is slightly decreased. It will affect the reception of the horizontally polarized signal, and when the vertical polarization voltage drops below the actual polarization switching transition point voltage setting value, the vertical polarization signal can be received. The number of series connected rectifier diodes is determined by the specific test conditions.
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