JPS6325798Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a television interference preventer for preventing interference waves in television reception.

Many factors can interfere with television reception.
For example, a fault current is induced in a television reception antenna and a power supply line by external noise or communication/broadcast waves, and this current enters through the input circuit of the television receiver, passes through the power supply circuit, and is grounded to the earth. At this time, the loop current couples to the input of the electrical circuit,
This appears as a beat disturbance in the image and audio output of the television receiver.

Devices that cause interference include industrial high-frequency equipment, automobile engine plugs, motor brushes, electrical contacts, discharge lamps, and corona discharge from power transmission and distribution lines. In addition, interference caused by communication/broadcast waves includes same-channel interference,
Alternatively, there may be fogging or interference from adjacent channels. High power radiation occurs near long wave, medium wave, short wave, and very short wave broadcasting and transmitting stations. Additionally, interference may occur due to these mutual modulations and cross-modulations.

The equipment affected is not limited to television receivers.
The same applies to video tape recorders (VTRs), stereo receivers, tape recorders, etc.

To prevent this interference, either receive the signal at a location far away from the source or reduce the transmit power.
Alternatively, it is necessary to reduce harmonic radiation.
Particularly in recent years, printed wiring boards have been widely used, and the shielding effect has deteriorated compared to the case of wiring on a conventional metal chassis. Furthermore, the overall gain of the television receiver is also increased, making it easier to receive interference waves.

This idea was made in view of the above circumstances,
The purpose is to provide a TV interference preventer that can effectively prevent interference waves.

An embodiment of this invention will be described below with reference to the drawings. In Fig. 1, 11 and 12 are input terminals of a TV interference preventer;
Connected to 12 are the center conductor and outer conductor of a coaxial cable that guides television waves received by a receiving antenna. A primary winding 14 of a ferrite transformer 13 is connected between these input terminals 11 and 12.
A capacitor 15 is connected between both ends of this primary winding 14.
is connected. One end of the secondary winding 16 of the ferrite transformer 13 is grounded, and the other end is grounded.
It is connected to the input terminal 18 of the VHF/UHF splitter 17. This duplexer 17 includes coils 19 and 2.
0, 21 and a capacitor 22, and a UHF band-passing transducer including capacitors 23, 24, 25 and a coil 26. One output terminal 2 of the duplexer 17
7 is transmitted through a high-pass transducer 31 composed of capacitors 28, 29 and a coil 30.
It is connected to the VHF output terminal 32. This VHF
The output terminal 32 is connected to an input circuit of a television receiver via a 75Ω coaxial cable. The other output terminal 33 of the duplexer 17 is connected to the UHF output terminal 35 via an unbalanced-balanced converter 34.
36. This UHF output terminal 35,
36 is connected to the input circuit of the television receiver via a parallel feeder for 200Ω.

The ferrite transformer 13 has holes 37 and 38 in a ferrite core 39 formed by penetrating two holes 37 and 38 in the center as shown in FIG.
It is constructed by winding a primary winding 14 on the input side and a secondary winding 16 on the output side two to three times. In this ferrite transformer 13, the primary winding 14 is not connected to the ground, while one end of the secondary winding 16 is grounded and connected to the ground portion of the branching circuit.

With such a configuration, the input terminals 11 and 12
The center conductor and outer conductor of the coaxial cable connected to the output side have no continuity with the output side under direct current. Therefore, the television signal passes through, but the fault current is coupled only through the interwinding capacitance.

FIG. 3 shows a printed circuit board 40 on which the ferrite transformer 13 is mounted.
One end of this printed circuit board 40 is an input-side copper foil section 41, and the other end is an output-side copper foil section 42. The copper foil section 41 on the input side and the copper foil section 42 on the output side are completely separated by a copper-free section 43 in the center, and the ferrite transformer 13 is indicated by A on this copper-free section 43. It is designed to be installed in parts. Note that the center conductor and outer conductor of the coaxial cable are connected to the connection point 44 of the copper foil section 41 on the input side, respectively.
45. Further, the duplexer 17 and the unbalanced-balanced converter 34 are installed at the portions indicated by B and C of the copper foil section 42 on the output side, respectively.
The center conductor and outer conductor of the coaxial cable connected to VHF output terminal 32 are connected to connection points 46 and 47, UHF
The parallel feeders connected to the output terminals 35 and 36 are connected to a connection point 48, respectively.

In the TV radio interference preventer having such a configuration, the TV radio waves from the receiving antenna are guided to the coaxial cable, input to the splitter 17 via the ferrite transformer 13, and are
Split into VHF signal and UHF signal. one side
After unnecessary components are removed from the VHF signal by a high-pass filter 31, the VHF signal is guided to a 75Ω coaxial cable connected to a VHF output terminal 32, and sent to a VHF tuner, which is an input circuit of a television receiver. The other UHF signal is converted into a balanced signal by the unbalanced-balanced converter 34, and then sent to the UHF output terminal 3.
The signal is guided to a 200Ω parallel feeder connected to terminals 5 and 36, and sent to the UHF tuner of the television receiver.

In this TV electromagnetic interference preventer, the low frequency unbalanced current flowing through the outer conductor of the coaxial cable on the input side is reliably removed by the ferrite transformer 13 and the printed circuit board 40, as shown in FIG. be able to. In other words, the attenuation amount is about 50 dB in the AM radio band, and more than 20 dB in the 27 MHz of amateur radio and CB (citizen band radio), so it can be sufficiently effective. Furthermore, leakage magnetic flux can be reduced and insertion loss can be reduced.

In FIG. 5, two of the above ferrite transformers 13 are connected, and a wave generator 49 is inserted and connected between them. In such a circuit configuration, although insertion loss increases, unbalanced and out-of-band balanced currents can be attenuated.

As mentioned above, according to the TV interference preventer of this invention, the ferrite transformer and the printed circuit board with completely separated input and output sides allow
Since interference waves can be effectively removed, stable television reception is possible.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a TV interference preventer according to an embodiment of this invention, Fig. 2 is a perspective view of a ferrite core used in the preventer of Fig. 1, and Fig. 3 is a perspective view of a ferrite core used in the preventer of Fig.
The figure also shows a printed circuit board, FIG. 4 is a frequency-attenuation characteristic diagram of the preventer of FIG. 1, and FIG. 5 is a circuit configuration diagram according to another embodiment of the invention. 11, 12... Input terminal, 13... Ferrite transformer, 17... Duplexer, 37, 38...
Hole, 39... Ferrite core, 40... Printed circuit board, 41... Copper foil part (input side), 42... Copper foil part (output side), 43... Copper-free part.

Claims (1)

[Claims for Utility Model Registration] (1) In a TV radio wave interference preventer inserted between a coaxial cable that guides received radio waves from a receiving antenna and the input circuit of a TV receiver, the input and output parts are an insulated printed circuit board,
A television radio wave characterized by comprising a ferrite core having two holes in the center, winding input and output windings around the holes, and a ferrite transformer installed on the printed circuit board. Obstacle preventer. (2) The television radio wave interference preventer according to claim 1, which is a utility model registration, and comprises a VHF/UHF duplexer connected between the output side of the ferrite transformer and the input circuit of the television receiver.