High frequency machine interference signal spectrum analysis
High frequency machine power output tube itself oscillating and output signals, so it is poor stability of the fundamental frequency, will be with the temperature and working conditions in the cabinet (output power regulation and the size of the workpiece, thickness, etc.) fluctuations in the change, although the change is only a few megahertz, it is possible to have individual interference signals from a certain channel to its transfer to the neighboring channel.
High frequency machine output power, high voltage (3kV) DC power supply current is also relatively large (1A or so), while its high voltage rectifier power supply is very simple, with four 1A/10kV high-voltage silicon pile plus a 0.1μF/8kV filter capacitors. As the filter capacitor capacity is too small, high-voltage DC power supply is actually 100Hz pulsating DC power supply, high-frequency machine output of high-frequency signals are actually modulated with a modulation system close to 100% of the 100Hz AC signals, which has no significant adverse impact on the performance of high-frequency machine, but can be non-equal amplitude oscillation signal to reduce the power consumption of the electronic tube to extend the service life of the electronic tube. So the essence of high-frequency machine interference with the TV is a modulated high-frequency signal acoustic interference, when the high-frequency machine interference signal strings into the TV, the TV screen will produce two wide horizontal stripes of 100MHz acoustic modulation-like interference, interference intensity is large, the two horizontal stripes all white, the intensity of the interference is small, the two horizontal stripes are distributed with a mesh ripples (with the general acoustic interference is different), and accompanying sound for the 100MHz AC sound. Measures to prevent and mitigate the interference of high-frequency machines
(1) build a plant to do a good job of shielding the system, with a 0.3 galvanized sheet or a small purpose of shielding around the wire mesh, will be 50mm iron pipe into the ground 2-3 meters, every two meters to play a shielding network connected to the iron pipe, so that the high-frequency signals are not easy to radiate from the plant, to play a role in the overall effect of shielding.
(2) the high-frequency machine frame and shell good grounding, strengthen the body shielding, reduce the body radiation is recommended to use a width of 50mm × 50mm or more, the length of not less than 2m angle iron into the ground as a grounding body, and then more than 10mm2 copper wire will be connected to the high-frequency machine racks and shells and grounding body. Connecting line should be as short as possible, can not be looped, try to avoid turning, so as to strengthen the shielding of the body part of the high-frequency machine, reducing the intensity of the interference signal radiated to the outside. If the car (room) room has more than one high-frequency machine, it is best to each high-frequency machine (or two neighboring units) are near the machine buried a ground line.
(3) adjust the location and direction of the high-frequency machine
If there are cables hanging on the outside wall of the house, it is best to set the high-frequency machine at the end away from the cable. In addition, the ordinary type of high-frequency machine tube chassis have at right angles to the two directions is fixed with galvanized iron plate on the galvanized angle iron frame shielding, radiation is weak, should be used in these two directions to the cable or near the TV users.
(4) It is recommended to purchase and use anti-interference type high-frequency machine
(5) do a good job of grounding the cable television network, choose the best location for the cable
High-frequency machine near the amplifier and stranded steel must be reliably grounded to strengthen its own shielding capacity. Cable hanging in the house with a high-frequency machine on the outside wall, to be selected in the reinforced concrete components (such as ring beams, cement more than also floor slabs) outside the measurement, do not choose the outside of the brick wall, so that the cable is subjected to radiation is weaker.
(6) adjust the position of the amplifier or cable
When the amplifier's entrance cable from the high-frequency machine is very close (within 10m), the amplifier can be shifted forward to the exit cable close to the high-frequency machine, because of the high level of television signals here, which is conducive to increasing the level of television signals and invasive interference with the level of the difference between the cable, or to adjust the trunking cable, so that it is slightly farther away from the high-frequency machine.
(7) ensure that the cable joints reliable
The connection between the amplifier as far as possible to use straight-through joints, ordinary line joints should be done in a standardized, reliable, special attention should be paid to the joints waterproofing, so as to avoid joints into the water caused by the outer conductor of the braided network moldy breaks, resulting in poor shielding and the string of interfering signals.
(8) and high-frequency machine close to only twenty or thirty meters within the user, the measures that can be taken are: 1 to ensure or improve the user's signal level, the user's entrance level of each channel to ensure that not less than 65dB, as far as possible to 75 ~ 80dB. 2 households do not use the user box, the entry line is directly connected to the TV with a plug, such as a number of televisions with a sealed type of branching (eg, Z106) or Distributor directly connected to the TV set.3 user indoor wiring cable must use qualified products or four shielded cable, prohibit the use of poor-quality cables, from the high-frequency machine within 10m of the user's best use of aluminum tube cable into the home.4 indoor TV set as far as possible without the use of plastic pressure injection-type plug line.5 good plug line, as far as possible, without the use of plastic pressure injection-type plug line (which is easy to desoldering and not easy to detect the internal), using handmade four shielded cable Plug line. 6 received a complaint of user failure, the first change a new plug line to try, if the problem is solved, then the user plug line plug cut off and redo, otherwise check the indoor cables and connectors, and even outdoor cable connectors.