High Frequency principle and principle of what are

　　Frequency plastic welding machine (referred to high-frequency machine, Taiwan, said high frequency , English Hing freguency plastic welder) the vast majority of users are small factories or home factories scattered settlements, the often varying degrees, affect nearby residents have cable TV, To this end, Kairon Equipment Co., Ltd. has been specialized engineers Investigative studies basically figure out the high-frequency interference on the cable characteristics, and found a number of high-frequency machine to prevent and mitigate interference cable way.

　　1, high frequency machine interference signal spectrum analysis

　　Frequency used by the local machine has two types, a) is the most common type of high frequency (hereinafter referred to as "ordinary machine"), the power of 2.5kW. Radiated interference signal frequency machine has three main parts: First, the bottom side of the table flat iron tubes and oscillation circuit, although there are two directions sealed thin metal, but the other two directions is removable door; Second, the high-frequency feeder table above, processing molds and fixtures, which is the main part of the radiation; Third, high-frequency switching table below and output adjustment variable capacitor, because of its close to the iron bench and chassis Case iron and lead very short, estimated the radiation is weak. 2) Anti-interfering frequency machine, it is only the high-frequency oscillation circuit installed in the round tube and the inner drum shielding, while other parts were not any shield, although it has anti-jamming effect, but the effect is limited, we measured obtaining the strength of the interference level is about 75% of an ordinary machine, will still interfere with the signal cable.

　　These two types of high-frequency machines belong to the self-excited high-frequency oscillator, which is characterized by the power output tube itself is oscillating tube, so the output frequency is not a single, but a band, one of the most frequency oscillation output called strong fundamental rest called harmonics. I measured the three sets of ordinary machines were fundamental frequency 32.50MHz, 32.80MHz and 33.65MHz. On both sides of the fundamental harmonic distribution, an ordinary machine total band between about 20 ~ 38MHz.

　　DS1240 field meter used for spectral analysis of frequency of lowest 46MHz, can not drive the fundamental and harmonic frequency signal group directly spectral analysis had to deal with it is the second harmonic spectrum analysis. As the intensity of the fundamental and harmonics that much difference, does not take into account all of a scan, centime high and low two scans, the scan results show that with an ordinary TV antenna supporting the use of high-frequency locomotive horns indirectly received The second harmonic of the fundamental level is close to 120dB, while the second harmonic harmonic level below 60dB majority in a difference of more than 60dB.

　　In addition to high-frequency machine output intensity of the fundamental and harmonic outside, as well as strength considerably higher harmonics of the fundamental harmonic of the second high may interfere with the corresponding channels on TV, and high-frequency author machine adjacent experimental observation done on several TV to prove the corresponding channel television image or audio layer are subject to different degrees of interference. Through testing and observation, that the fundamental and harmonic frequency machine frequencies below 45MHz, outside the band in the cable, the cable does not interfere with the interference of the cable is their second higher harmonics.

　　As much below the fundamental harmonic intensity, but the frequency bandwidth, higher harmonic components are complex, the author through field observations concluded that it is possible for less than 10m away from the high-frequency machine TV many (or even all) channel image and the sound of interference; television on distance, which may sound a few TV channels open into the interference of varying severity, and specific interference which channels are difficult to predict.

　　The power output of high-frequency machine and the output signal oscillating tube itself, so its poor stability of the fundamental frequency will be with the cabinet temperature and operating conditions (output power adjustment and the workpiece size, thickness, etc.) fluctuate, although varies only a few tenths of megahertz, it may be by an individual channel interfering signals transferred to the adjacent channel.

　　The output power high frequency machine, high pressure (3kV) DC power supply current is relatively large (1A or so), but it's big high voltage rectifier power supply is very simple, with four 1A/10kV voltage silicon stack plus a 0.1μF / 8kV filter capacitor. Since the filter capacitance is too small, high voltage DC power is actually 100Hz pulsating DC power supply, high-frequency signal output by the machine actually is modulated close to 100% modulation of the AC signal of 100Hz, which is high machine working adversely affect the performance is not much, but it may be due to non-amplitude oscillation signal while reducing the power consumption of the tube to extend tube life. So the essence of high-frequency machine interference TV is a high-frequency signal modulation hum interference, when the high frequency interference signals machine into a TV series, it will generate on the TV screen two wide stripes of 100MHz hum modulation-shaped interference, the interference intensity, the two bars all white, disturbance intensity hours stripe are distributed in two corrugated mesh (hum interference with the general type), and the sound was 100MHz hum.

　　2, high frequency machine interference signal propagation and invasive special cable trunk cable and user assignment is China mainline cable are laid along the exterior housing users, only in neutral locations plus vertical cement pole, no ride hanging in the house before and after the user electricity poles, many of the main line of the trunk cable and the cable away from the user-assigned frequency machine after only a few meters away, the nearest less than 1m (houses length 10 ~ 20m, 2nd floor room facilities generally machine, 2nd floor wall drawn steel wire hanging cable, cable and high-frequency machine nearly horizontal parallel), followed by a few levels below a user-trunk amplifier or amplifiers, or directly assign users. If the interference signal frequency machine is the first to be dry (main) cable receiver into which the string, and then (by the amplifier) ​​and then through the cable distribution into the user's TV, then the TV will be subject to all of the following frequency machine interference. But the reality is not the case, usually only sporadic, "migratory" interference, and high-frequency machines are in close proximity to a larger proportion of consumer complaints, a little far smaller proportion of users, from the high-frequency machine users outside no complaints 500m too. This confirms that the high-frequency interference signals are not machine dry before invasion (main) cable, then (by the amplifier) ​​transmitted through the cable to the TV. Although the high-frequency machine radiated interference signal strength is large, but dried (main) cable (-12 -9 physical foaming or cable) around the shielding loss of up to 80dB, invade the level of interference within the cable does not high, far less than the television signal level. The author uses spectrum analysis measurements over a 80m long copper braid outer conductor of the cable end -9 physical package bubble frequency machine interference level, which is a user-assigned mainline, high frequency machine from the user amplifier 18m, 3m away from the cable (in the interval of a wall), the measurement amplifier is powered down, remove cable households (grafting 75Ω load resistor), the measured frequency machine intrusive interference level: the second harmonic <20dB, television signal level to than its height 42 ~ 60dB or more.

　　High Frequency Radiation carried out large amounts of data tests are shown in Table 1 and Table 2, two tables are the propagation of high frequency interference signals machine test records, the use of German forces DS1240 Strength Meter measured frequency spectrum analysis mode, the measurement of high frequency interference wave machine work continuously for one scan time. There are two kinds of signal receiving antenna, A is ordinary -5 3m cable ends not connected resistors, and in the near field intensity at the outer conductor girdling week simulation shielded cable damage.

　　Since high frequency machine selector switch in a different position (there are five stalls, measuring set intermediate file), output adjustment capacitor tune in a different location and test dummy workpiece (continuous high-frequency machine can not put real work) the thickness of the are associated with different radiation intensity, coupled with the test method used by high-frequency machine can not accurately determine the actual radiation field intensity, so two tables of data for analysis of relevant characteristics only for reference.

　　Table 1 High-frequency local signal propagation test in the wilderness recording units: (dB)

　　From the high frequency machine 10m 30m 70m 100m 200m 300m 400m

　　Receiving mode ABABABABABABAB

　　Second harmonic <2090 <2070 <2065 <2045 <2030 <20 <20 <20 <20

　　Third harmonic <2072 <2063 <2053 <2048 <2050 <2042 <20 <20

　　Ninth harmonics <20653865 <2055 <2052 <2046 <2030 <20 <20

　　Sixth harmonic 35654573 <2053 <2060 <2043 <2033 <20 <20

　　Mean level 73.5 67.5 56.6 51.3 42.3 31 <20

　　Table 2 High Frequency signal transfer through the wall propagation test recording units: (dB)

　　House number four District 274 District 284 District 294 District 304 District 314 District 324 District 33

　　Distance frequency machine 2m 6m 9m 13m 17m 20m 28m

　　Wall channel number 1234568

　　Receiving mode ABABABABABABAB

　　Second harmonic 50 1,054,710,025,902,283 <2067 <2065 <2072

　　Third harmonic 45954086 <2067 <2060 <2062 <2058 <2060

　　Ninth harmonics 55 100,428,140,783,270 <2070 <2070 <2052

　　Sixth harmonic 58903578 <2060 <2060 <2052 <2052 <2050

　　Mean level 48.3 9541 86.3 <26 73.8 <24 68.3 <20 66.8 <20 61.3 <20 58.5

　　As can be seen from the measurement results, the normal -5 cable than ten meters high frequency machine interference level received in less than 20dB, and the home of the television signal level (65dB) difference of 45dB or more, does not interfere with television signals ; -5 cable shield the damage, even to 300m beyond the received interference signal will still interfere with the signal cable, the TV system by the high-frequency machine money interference shielding is mainly due to a problem itself.

　　After careful analysis of the measured data and the actual investigation that invade TV interference signal has three main ways:

　　First, the shielding effect of the cable outer conductor invalidate or weaken after receiving antenna into a high-frequency machine interference signals into TV, so the TV suffers interference, in which more than 80% of failures are connected to the user box and the TV plug cord outside conductor welding desoldering (pressure inside the plastic from the outside can not see), then you can just redo the plug. There is then a branch line from the customer premises without using splitters or shielded cable is not connected, or use shielded cables and even poor performance dual-core sheathed cable, or bitten off by rats caused by outer conductor.

　　Second, a few TV's own poor shielding, high frequency machine interference signal directly into the TV series, when the TV frequency machine closer distance, the poor performance of the television screen the most prone to this condition. Inspection methods are: the TV election in the high-frequency interference that channel machine, and then unplug the TV signal plugs, wishful interference on the screen at this time disappeared, indicating that the TV itself shielding performance is better; contrary If there is still interference at this time the TV screen, and even become more severe, indicating that this TV shielding performance is poor, their machine will receive high-frequency interference signals.

　　Third, into the family line and the user plugs commonly used -5 cable, it shielded cable shielding loss is smaller than four, within tens of meters away from the high-frequency machine when intrusive interference signals may affect TV signals. If the cable quality is no problem, this effect is minor, but the individual channels in the two bars appear on the location of subtle textured.

　　Described above, the money television dried (main) cable shielding normal circumstances, high-frequency interference signal is not the first machine intrusive cable transmission through the cable to the distance, but directly to the distance from the radiation propagation space, but transmission distance is limited, usually no more than 500m.

　　3, to prevent and mitigate interference measures frequency machine

　　(A) when the plant was built to do shielding system, with 0.3 galvanized sheet or a small wire mesh shielding purposes around the 50mm iron pipe into the ground 2-3 meters every two meters to fight a will shield with iron pipe connection, so that high-frequency signal is not easy to radiate out from the factory, played overall shielding effect. ?

　　(2) high-frequency machine frame and the shell is well grounded, strengthen the body shield, reduce body radiation

　　Recommended width of 50mm × 50mm or more, the length is not less than 2m of angle iron into the ground as grounding, then 10mm2 copper above the high-frequency machine frame and the shell is connected with the grounding. Connection should be as short as possible, do not circle, try to avoid turning, so you can enhance high-frequency portion of the shield machine body, reducing the intensity of the interference signal radiating outward. If the car (room) room at more than one frequency machine, high frequency machine best each (or two adjacent) are buried in the machine next to a nearby ground.

　　(3) Adjust the position and direction of the high-frequency machine

　　If the housing wall hanging cables, high frequency machine is best to set away from the end of the cable. In addition, ordinary type high frequency machine tube chassis in two directions at right angles to success is to use galvanized steel galvanized angle iron rack fixed to the shield, the radiation is weak, should be based on these two directions, or near the front of the cable television users.

　　(4) the proposed purchase and use of tamper-frequency machine

　　(5) make the grounding cable networks, selecting the best location for the cable

　　High-frequency amplifier and strand near the machine must be grounded in order to strengthen its shield capabilities. Cables hanging in a high-frequency machine housing wall, to choose in the reinforced concrete structures (such as ring beams, cement more and floor) outside the test, not to vote on the brick wall outside, so that the cables exposed to radiation weaker.

　　(6) Adjust the position of the amplifier or cable

　　When the amplifier is close to the entrance when the cable away from high frequency machine (10m or less), the amplifier can be moved forward, to export the cable near high-frequency machines, because here the television signal level is high, help to increase television signals interfered with invasive level difference, or adjust the trunk cable, making it a little far away from the high-frequency machine point.

　　(7) ensure reliable cable connector

　　The connection between the amplifier as far as possible through-type connector, connector lines to do ordinary norms, reliability, special attention should be waterproof joints, causing water to avoid joint outer conductor braid mold off, leading to poor shielding string into the interfering signals.

　　(8) with only two meters high frequency machine within close range of users, the measures can be taken: a guarantee or improve user signal level of each channel entry-level users to ensure that no less than 65dB, as far as possible to 75 ~ 80dB. 2 inside without user boxes, home line directly connected to a TV with plug and, if more than one is the TV is using sealed splitter (eg Z106) or distributor directly connected to the TV. 3 users cables must be laid indoors Qualified or four shielded cable, disable inferior cable less than 10m away from the high-frequency machine user is best to use aluminum cable households. 4 Indoor TV as much as possible without plastic injection pressure plug line. 5 good plugs, try not to plastic injection pressure plug wire (its internal easy desoldering and easy to find), the use of hand-crafted four shielded cable plugs. 6 users fault complaints received, the first for a new plug wire to try, if the problem is resolved, then the user plug cord cut redo, otherwise then check the indoor cables and connectors, and even outdoor cable connector.