JPH02288506A - Rf modulator - Google Patents

Abstract

PURPOSE:To make an optional trap frequency stable by differentiating the direction of the aperture of two coils used for a trap circuit. CONSTITUTION:The direction of the aperture of both coils 14, 15 of a trap circuit is made different, then the coil 14 is mounted on a printed circuit board 17 so that the coil 14 is made to a right angle in the direction of the aperture of the coil 15. The coupling between both the coils 14 and 15 is made coarse and the mutual induction coupling coefficient in the combined inductance of the coils 14, 15 is almost neglected. Thus, the combined inductance when the switch 16 is thrown to the position of L channel is L14+L15 and the trap frequency is set by the individual inductance. Thus, the change in the trap frequency is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an RF modulator used in the field of video equipment such as VTRs.

As shown in FIG. 3, the conventional RF modulator converts an audio signal input from an input terminal 1 into FM using an FM modulation circuit 2, and then converts it into an upper side wave using a carrier oscillation circuit 3 and an audio mixer circuit 4. The audio RF is converted into an audio RF multiplied signal as a lower side wave, and the lower side wave (-f's) is removed by the trap circuit 5.
Double signal. This audio RF multiplied signal is then input through the input terminal 6.

The carrier oscillation circuit 3 and the video modulation circuit 7 combine the resulting video RF signals, remove unnecessary components in the first-stage filter circuit 8, and output the TV multiplied signal from the output terminal 9. As shown in FIG. 2, the trap circuit 6 includes a capacitor 12 connected between the input terminal 1o and the output terminal 11, a capacitor 13 connected in parallel between the capacitor 12 and the ground, and coils 14 and 15 connected in series. Lc provided between the connection body, the connection point of coils 14 and 15, and ground
Switch 1 to change the trap frequency of h and Hoh
It consists of 6. Then turn switch 16 to Lch
When it is on the side, the inductance is the combined inductance of coils 14 and 15.

When set to the Hch side, the inductance is only that of the coil 14. The characteristics of the trap circuit 6 are such that, for example, when the switch 16 is turned to the Hch side, the resonance frequency is set so that the audio RF signal (fs) is passed through the parallel resonance circuit formed by the capacitor 13 and the coil 14. The trap frequency is set so that the series resonant circuit formed by the parallel resonant circuit and the capacitor 12 removes the lower wave (-f's) of the audio RF signal.

The coils 14 and 15 of the conventional trap circuit are mounted on the mounting surface of the printed circuit board 17 with their opening directions facing each other, as shown in FIG. Note that 18 is a wiring pattern.

Problems to be Solved by the Invention In such a conventional device, the coils 14 and 15 are mounted with their opening directions facing each other, so when the switch 16 is set to the Lch side, the winding directions of the coils 14 and 15 are the same. Therefore, a summation connection occurs, and a mutual inductive coupling coefficient=M occurs between both coils 14.15, and the combined inductance of the coil 14.15 becomes Lla + L15 +2 M. However, due to floating, tilting, etc. that occur when the coils 14 and 15 are inserted into the printed circuit board 17, the mutual inductive coupling coefficient=M between the two coils changes. Therefore, there was a problem in that the trap frequency changed and therefore the inductance of the coils 14, 15 had to be adjusted after this mounting.

The present invention solves the above problems and aims to eliminate this change in trap frequency.

Means for Solving the Problem In order to solve this problem, the present invention provides a coil 14.15.
are mounted on a printed circuit board with different opening directions.

Function: The present invention has the above-described configuration, and since the opening directions of the coils are different, the mutual inductive coupling coefficient 2M decreases, and the two coils become loosely coupled.

Therefore, changes in the composite inductance due to floating, tilting, etc. when the coil is inserted into the printed circuit board are eliminated.
When creating an RF modulator, it is possible to eliminate the step of adjusting the coil inductance.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings.

The RF modulator is the same as shown in FIG. 3, and the trap circuit 5 is the same as shown in FIG. However, in this embodiment, since the opening directions of the coils 14 and 15 are different from each other as shown in FIG. Implemented. As a result, the coupling between the side coils 14 and 15 is loose coupling.
In the combined inductance, the mutual inductive coupling coefficient 2M can be almost ignored, and the combined inductance when the switch 16 is set to the Lch side is L11+L1□.The trap frequency can be set by each inductance. In addition, in this embodiment, in addition to the arrangement of the coils 14 and 16, the wiring pattern 18 between the coils 14 and 15 is such that the soldering of the coils 14 and 16 is thicker than the land portion, thereby reducing the pattern inductance. Furthermore, the influence of the mutual inductive coupling coefficient 2M is reduced.

Furthermore, effects can also be obtained by winding one of the coils 14, 15 in the opposite direction.

Effects of the Invention As described above, according to the present invention, by making the opening directions of both coils different, it is possible to stabilize any trap frequency when manufacturing an RF modulator. Therefore, it is possible to eliminate the need for adjusting the coil and reduce the adjustment process for the RF modulator.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a perspective view of a coil 14 16 used in a trap circuit of an RF modulator according to an embodiment of the present invention mounted on a printed circuit board 17.
b is the circuit diagram and characteristic diagram of the trap circuit of the R1 modulator, Fig. 3 is a block diagram of the RF modulator, and Fig. 4 is the coil 14.15 used in the one-wrap circuit of the conventional RF modulator FIG. 2 is a perspective view of the device mounted on a printed circuit board 17. 1... Input terminal, 2... FM modulation circuit, 3... Carrier oscillation circuit, 4... Audio mixer circuit, 5... Trap circuit, 6...
...Input terminal, 7...Video modulation circuit, 8.
...Filter circuit, 9...Output terminal. 1o...Input terminal, 11...Output terminal, 12...Capacitor, 13...Capacitor, 14...Coil, 16... ... Coil, 16 ... Switch, 17 - ... Printed circuit board, 18 ... Wiring (turn. Name of agent: Patent attorney Shigetaka Awano and 1 others) Prefectural map fs

Claims (1)

[Claims] The trap circuit includes a first capacitor connected to its output terminal, a second capacitor connected in parallel between the first capacitor and ground, and a series connection of the first and second coils. and a switch provided between the connection point of the first and second coils and ground, and the first and second coils are mounted on a printed circuit board with their opening directions different.