High frequency interference problem solution example

High frequency plastic welding machine (referred to as the high-frequency machine, Taiwan, said high-frequency English Hing freguency plastic welder) users the vast majority are small factories or family factory, scattered in settlements within, often varying degrees of impact on nearby residents to watch cable TV. To this end, the engineers specialized of basically figured out the cable interference characteristics of high frequency machine, worked out some way to prevent and reduce the high frequency machine interference cable.

A high-frequency machine interference signal spectrum analysis

There are two types of high-frequency machines used by the local 1) the vast majority of the ordinary type of a factory production of high-frequency machine (hereinafter referred to as "ordinary machines"), and the power of 2.5kW. Out high-frequency machine radiation interference signals there are three main parts: First, the iron flat bottom of the table side of the tube and the oscillation circuit, although there are two directions to seal the thin metal, but the other two directions are removable door; two high frequency feeder of the table above, the processing mold fixture, which is the main parts of the radiation; bench below the high-frequency switch and output to adjust the variable capacitor, because of its close to the iron table and chassis shell of iron and lead is very short, it is estimated that the radiation is weak. 2) anti-interference high-frequency machine, only the high-frequency oscillation tube and circuit installed in a round metal drum shield, while other parts were not any shield, although its anti-interference effect, but the effect is limited, we measured obtaining the interference level of intensity is about 75% of the ordinary machine will still have a cable TV signal to interfere with.

More than two types of high-frequency machine belongs to the self-excited high-frequency oscillator, which is characterized by the power output tube is oscillating tube, so the output frequency is not a single, but a band, one of the frequency of the oscillation output most strong is called the fundamental, called harmonic. I measured the ordinary fundamental frequency 32.50MHz, 32.80MHz and 33.65MHz. Harmonic distribution on both sides of the fundamental ordinary machine band around between 20 ~~ 38MHz.

Using the Signal Level Meter for spectrum analysis, the minimum analysis frequency of 46MHz spectrum analysis, not directly on the fundamental and harmonic signal group of high-frequency machine, now had to deal with its second harmonic spectrum analysis. Fundamental and harmonic intensity that much difference, a scan can not take into account all centime high and low two scans, the scan results show that ordinary TV supporting claw antennas in the high-frequency locomotives received indirect fundamental second harmonic level near 120dB, most of the harmonic of the second harmonic level 60dB below a difference of more than 60dB.

In addition to the fundamental and harmonic of the output of high-intensity, high frequency machine while there is considerable intensity high harmonic of the high harmonic of the fundamental may interfere with the corresponding television channels, I and the high-frequency machine adjacent to several TV experiment on observation proved the corresponding channel television image or sound layer by varying degrees of interference. Through testing and observation that high-frequency machine fundamental and harmonic frequencies below 45MHz, will not be formed on the cable outside the cable TV band, interference, interference with cable TV is their high-order harmonic.

Harmonic intensity Biji Bo low bandwidth, high harmonic components are complex, through field observation I think it may be less than 10m from the high-frequency machine, TV (or even all) channel image interfere and sound; distance TV may be the sound of a small number of TV channels open into the interference of varying severity, and specific interference which channels are difficult to predict.

Tube oscillation and the output signal to the power output of the high-frequency machine, so its fundamental frequency is less stable, as the temperature inside the cabinet and working conditions (the adjustment of output power and workpiece size, thickness, etc.) of the changes and fluctuations, although change of only a few tenths of MHz, there may be individual interference signals from a channel to its adjacent channel.

Output power of the high-frequency machine, large high-voltage (3kV) DC power supply current (1A), while its high-voltage rectifier power supply is very simple, by four 1A/10kV high voltage silicon stack plus a 0.1μF / the 8kV filter capacitors. Filter capacitance is too small, high-voltage DC power supply is actually 100Hz pulsating DC power supply, high frequency machine output of high-frequency signal is actually modulated modulation close to 100% of the 100Hz AC signal, high frequency machine little adverse impact on performance, but it can reduce the power consumption of the tube, the amplitude oscillation signal to extend the life of the tube. The substance of the high-frequency machine interfere with TV is a modulation of the hum of the high-frequency signal interference when the interference signal of the high-frequency machine in series TV, two wide bars on the TV screen, 100MHz hum modulation-like interference, the interference intensity, all the white bar, the disturbance intensity hours, two bars, the distribution of mesh corrugated (interference with the general hum), and sound compared to the 100MHz hum.

2, high-frequency machine interfere with the signal propagation and invasive special cable trunk cable and user allocation mainline China cables are laid along the housing, the external walls of the user only in neutral locations plus cement pole, did not take to hang around the customer premises electricity poles, the number of trunk cable and user distribution main line cable after only a few meters away from the high-frequency machine, the most recent less than 1m (houses Length 10 ~ 20m, 2nd Floor of the general room facilities machines, 2nd Floor, wall drawing steel stranded wire hanging cable, cable and high-frequency parallel to the approximate level), below followed by a few trunk amplifier or a user amplifier, or directly to the user allocation. If the interference signal of the high-frequency machine is first dried (main) cable to receive the string into one, and then (via the amplifier) and then enter the user's TV via cable distribution, then its all TV will be subject to high frequency the interference of the machine. But the reality is not the case, usually only sporadic, "migratory" interference with the high-frequency machine are in close proximity of the proportion of customer complaints, a little far smaller percentage of users, no complaints from the users outside of the 500m high frequency machine before. This proves that high-frequency interference signal of the first invasive stem (main) cable, and then (via the amplifier) and spread to the TV via cable. Although the high-frequency machine radiation interference signal strength, but shielded cable (-12 or -9 physical foaming cable), stem (main) line loss up to about 80dB, invasive to the level of interference within the cable will not high, far less than the TV signal level. I use the spectral analysis method to measure the outer conductor of a 80m long copper braid -9 physics package bubble cable high-frequency end of the machine interference level, which is a user allocated the main line of high frequency from the amplifier 18m from the cable 3m (in the interval of a wall), when measuring amplifier power, home cable relieved (divert 75Ω load resistance), as follows: high-frequency machine interference level measured invasive second harmonic <20dB TV signal level to more than 42 ~ 60dB higher than its

High frequency machine radiation data test, high frequency machine interference signal propagation test records are listed in Tables 1 and 2, two tables are measured Deli DS1240 Signal Level Meter spectrum analysis, measurement of high frequency continuous work an interference wave scan time. There are two signal receiving antenna, A is 3m ordinary -5 cable, do not take at the end of resistance, and the outer conductor girdling week, near Signal Level Meter Moot shield damage the cable.

High-frequency high voltage selection switch to a different location (5 files, measurement set intermediate file), output tuning capacitor tune in a different location and test the workpiece (High Frequency of continuous work can not put real workpiece) thickness and the radiation intensity is related with the test method can not accurately determine the actual field strength of high-frequency radiation, so the two tables of data can only be analyzed relevant characteristics reference.

Table 1 high-frequency machine test signal is spread in the wilderness recording unit: (dB)

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

Receiving Mode A B A B A B A B A B A B A B

Second harmonic <2090 <20 70 <2065 <2045 <2030 <20 <20 <20 <20

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

Nine harmonics <20,653,865 <20 55 <2052 <2046 <2030 <20 <20

Sixth harmonic 35,654,573 <20 53 <2060 <2043 <2033 <20 <20

Average level of 73.5 67.5 56.6 51.3 42.3 31 <20

Table 2 high-frequency machine signal to wear the dissemination of test records units of wall transfer: (dB)

Building four District 274 District 28 Region 4 294 District 304 District 314 District 324 District 33

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

The partition Road 1 2 3 4 5 6 8

Receiving Mode A B A B A B A B A B A B A B

Second harmonic 5,010,547,100,259,022 83 <20 67 <2065 <2072

Third harmonic of 45 95 40 86 <20 67 <2060 <2062 <2058 <2060

Nine harmonic 551,004,281,407,832 70 <2070 <2070 <2052

Sixth harmonic 58,903,578 <20 60 <2060 <2052 <2052 <2050

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

From the measurement results can be seen that the normal -5 cable to receive more than ten meters high frequency machine interference level less than 20dB, and the home of the TV signal level (65dB) difference of 45dB or more, will not interfere with the cable TV signal ; -5 cable shield damage, other than to 300m receives the interference signal will still have a cable TV signals interfere, so wealthy television system by high frequency machine interference a problem mainly due to its shielding.

By careful analysis of the measurement data and the actual survey, that the interference signal intrusion TV approaches are mainly three kinds:

First, the failure or weakening of the cable outer conductor shielding effect, into the receiving antenna to receive high-frequency machine interference signal into the TV, TV disturbed more than 80% of failure is connected to the user box and the TV plug cord conductor weld sealing off (pressure in the plastic from the outside can not see), then redo the plug can be. There is a customer premises connected branch line does not use splitter or did not connect the shield wire or cable shielding performance poor or even dual-core sheathed cable, or the outer conductor bitten off by rats caused.

Second, a small number of TV's own shielding performance, high-frequency interference signal of string directly into the TV when the TV distance high frequency machine closer, shielding performance TV is the most prone to this situation. The test approach is: the TV is selected in the high-frequency machine interference channel, and then unplug the TV signal plug wire interference on wishful screen disappears, indicating that the shielding performance of the TV itself better; the contrary If the TV screen is still interference, and even become more severe, indicating that the shielding performance of this TV is poor, will receive the interference signal of the high-frequency machine.

Into the family line and user plug wire is commonly used -5 cable shielding loss is smaller than the quad-shielded cable, the intrusion of the interference signal in the tens of meters or less from the high frequency machine will affect the TV signal. If the quality of the cable is no problem, this effect is slight, but the individual channels on the location of the two bar fine textured.

The above description, the money to television stem (main) cable shielding normal circumstances, the interference signal of the high-frequency machine, not to invade cable through the cable to the distant spread, but directly to the distance from the space radiation spread, but The propagation distance is limited, usually no more than 500m.

To prevent and reduce high-frequency machine interference measures

Do a good job of shielding of the system (1) to build the plant, around 0.3 galvanized sheet or the purpose of barbed wire shielding of 50mm iron pipe driven into the ground 2-3 m, at intervals of two meters to play one, will be shielded connection with the iron pipe, so that the high-frequency signals is not easy to radiate out from the factory, played overall shielding effect. ? (2) high-frequency machine rack and shell a good grounding, strengthening the body shielding, to reduce body radiation suggested using the width of 50mm × 50mm or above, the length is not less than 2m, angle iron driven into the ground as the grounding, and then 10mm2 copper wire connected to the rack and enclosure grounding of high-frequency machine. The connection should be as short as possible, non-circular motion to avoid the turn, this may enhance the shielding of the high-frequency machine body part, reduce the external radiation intensity of the interference signal. Car (room) more than one high-frequency machine, it is best to each high-frequency machine (or adjacent two) to a nearby buried next to the machine ground.

(3) Adjust the high frequency machine position and orientation

If the housing wall hanging cable, high frequency machine is best set away from the end of the cable. In addition, the ordinary high-frequency machine tube chassis successful two directions at right angles is fixed with galvanized iron rack of galvanized angle iron shielding, radiation is weak, should both directions in front of the TV cable or near users.

(4) the proposed purchase and use of anti-interference high-frequency machine

(5) to do the grounding of the cable television network, selecting the best location of the cable

The high frequency near the amplifier and strand must be grounded in order to strengthen self-shielding capability. Suspension cable has a high frequency machine housing wall, to choose in the steel and concrete components (such as the ring beam, cement multi-floor), measured, not to vote in the brick wall the outside so that the cable is exposed to radiation is somewhat weaker.

(6) Adjust the amplifier or cable location

(10m or less) when the amplifier entrance cable from the high-frequency machine close to the amplifier can be forward instead of the export cable near high-frequency machine, because here TV signal level is high, the increase of television signals and intrusive interference electric adjustment, or adjustment of the trunk cable, making it a little far away from the high-frequency machine.

(7) to ensure reliable cable connector

Connected to the amplifier as far as possible straight-joint, common line connector to do a standardized, reliable, and should pay particular attention to the joints waterproof connector in order to avoid the water causing the outer conductor braid mold off, resulting in shielding poor series with the interference signal.

(8) and high-frequency machine, close within two meters of the user, the measures to be taken are: a guarantee or improve the level of the user signal, the channel user entry level to ensure that not less than 65dB, as far as possible to 75 ~ 80dB. 2 without the user box, home line plugs directly connected to a TV, if more than one TV Sealed splitter or the splitter directly connected to a TV. 3 user indoor laid cable must be a qualified product, or quad-shielded cable, disable, poor quality cable, users within 10m from the high-frequency machine is best to use aluminum pipe cable households. 4 indoor TV as much as possible without plastic injection pressure plugs online. Good plug wire, try not to plastic injection pressure plug wire (its internal sealing off easy, not easy to find), the use of hand-made four-shielded cable plug cable. Receiving the user fault complaints, change a plug wire test what, if the issue is resolved, then the user plug cord cut to redo, otherwise check the cables and connectors of the indoor and even outdoor cable connector.