JPH0418262Y2 - - Google Patents

Description

[Detailed explanation of the invention] <Technical field> This invention re-modulates the left and right audio signals obtained from a TV receiver, VTR, etc. and transmits them.
Regarding FM stereo transmission circuit.

<Prior art> Conventionally, TV receivers and VTRs have built-in FM stereo transmitter circuits, and the left and right audio signals obtained by receiving audio multiplex broadcasts are FM-modulated and transmitted, and then transmitted as normal signals at a remote location. There are FM receivers such as radio cassette recorders that allow you to easily listen to stereo sound.

In the FM stereo transmission circuit used in such cases, for example, when the 31.4KHz subcarrier component of the audio multiplex broadcast and the 15.7KHz TV horizontal synchronization signal are superimposed on the left and right audio signals obtained from the audio multiplex broadcast, the radio On the FM receiver side such as a cassette recorder, a beat may occur between the FM stereo pilot signal and the FM stereo pilot signal after demodulating the FM broadcast signal.
This causes problems such as noise in the TV horizontal synchronization signal. For this reason, the above 31.4KHz subcarrier component and 15.7KHz
It is desirable to provide a trap circuit that attenuates the TV horizontal synchronization signal.

However, when such a trap circuit is provided, a bass component may be induced in the reactance coil constituting the trap circuit by an external magnetic field from a deflection yoke or the like, which causes noise during FM reproduction. Therefore, in the conventional FM transmitter circuit,
The trap circuit is placed in a position and direction that is not affected by external magnetic fields, but in this way,
It is important to always set the installation position of the trap circuit at the optimal location, especially in response to demands for downsizing of equipment.
This can be difficult due to many design constraints.

Moreover, in the past, sufficient consideration was not given to the winding direction of each reactance coil in the trap circuit, and both coils were used with both coils oriented in the same winding direction. Therefore, when the buzz component A is induced in each reactance coil of the trap circuit,
As shown in FIG. 2a, the induced buzz components A have the same polarity. Therefore, the output signal of the trap circuit for the left audio signal is L+A, and the output signal of the trap circuit for the right audio signal is R+A. When these audio signals are given to the transmit matrix circuit, the main channel signal extracted from the transmit matrix circuit is (L+A)+(R+A)=L+R
+2A, the sub-channel signal is (L+A)-(R+
A)=LR. Then, the main channel signal L+R and the sub-channel signal L-R+2A are each FM-modulated and transmitted. When this FM broadcast is received by an FM radio, etc., the left audio signal extracted from the reception matrix circuit is (L+R+2A)+(L-R)=2L+2A, and the right audio signal is (L+R+2A)-(L- R)=2R+2A. That is, the buzz component is simultaneously reproduced by the left and right speakers, resulting in large noise.

In addition, when the audio multiplex signal is monaural broadcasting, only the main channel signal L+R+2A obtained by the transmission matrix circuit 12 is FM-modulated, and then
Since it is transmitted from the transmitting antenna 16, this main channel signal L+R+2A becomes the output of the receiving matrix circuit as it is, and therefore, as in the case of stereo broadcasting, the buzz component is simultaneously reproduced from the left and right speakers, resulting in large noise.

<Purpose of the invention> The present invention has been made in view of the above-mentioned problems, and is designed to prevent FM demodulation caused by an external magnetic field to the reactance coil of the trap circuit, both during stereo broadcasting and monaural broadcasting. It is an object of the present invention to effectively reduce the generation of subsequent buzz sounds.

<Structure of the invention> In order to achieve the above-mentioned purpose, this invention
The left and right audio signals obtained from a TV receiver, etc.
After passing through a trap circuit consisting of a resonant circuit,
The transmission matrix circuit converts the main channel signal and sub-channel signal, and both channel signals are converted to FM.
In the FM stereo transmission circuit that modulates and transmits, the winding directions of the reactance coils forming the trap circuit are set in opposite directions depending on the left and right audio signals.

Therefore, even if a buzz component is induced in the reactance coil by an external magnetic field, the polarity of the buzz component contained in the right audio signal and the left audio signal will be reversed. As a result, the polarities of the buzz components included in the left and right audio signals obtained after FM demodulation are also reversed, and the sound pressure level of the buzz components audibly decreases during playback. Further, when the audio signal is monaural, the main channel signal output from the transmission matrix circuit does not contain a buzz component, so that the influence of the buzz component does not appear during reproduction.

<Embodiment> An embodiment in which the FM stereo transmission circuit of the present invention is built into a TV receiver will be described below.

FIG. 1 is a block diagram including the FM stereo transmitting circuit of the present invention. In the same figure, code 1 is TV
The FM stereo transmitting circuit 2 built into the receiver is an FM receiving circuit built into, for example, a stereo radio cassette recorder. 4 is an input terminal for an audio multiplex signal; 6 is an audio multiplex demodulation circuit that demodulates the audio multiplex signal into left and right audio signals L and R; 8a, 8b;
is the 31.4KHz subcarrier component of the audio multiplex signal mixed into the left and right audio signals L and R, and the first trap that traps the 15.7KHz horizontal synchronization signal included in the video signal.
This is the second trap circuit. Both trap circuits 8
Both a and 8b are composed of LC resonant circuits,
The winding directions of the reactance coils 10a and 10b are set in opposite directions depending on the left and right audio signals L and R. 12 are left and right audio signals L, R
14 is an FM modulation circuit that performs FM modulation on both channel signals; and 16 is a transmitting antenna. In addition, 18 is a receiving antenna, 2
0 is an FM demodulation circuit, and 22 is a receiving matrix circuit.

In the FM stereo transmission circuit 1 of this embodiment, when the audio multiplex signal input from the input terminal 4 is input to the audio multiplex demodulation circuit 6, the audio multiplex demodulation circuit 6
demodulates this multiplexed audio signal into left and right audio signals L and R, and outputs a stereo/monaural discrimination signal depending on whether the multiplexed audio signal is a stereo broadcast or a monaural broadcast. This stereo/monaural discrimination signal is then given to the FM modulation/RF amplification circuit 14. The FM modulation/RF amplification circuit 14 controls the FM stereo transmission mode according to the stereo/monaural discrimination signal. That is, if the audio multiplex signal is a stereo broadcast, the mode is switched to stereo transmission mode, and if it is monaural broadcast, the mode is switched to monaural transmission mode.

The left and right audio signals L and R output from the audio multiplexing and demodulating circuit 6 are sent to the first and second trap circuits 8 in the next stage.
The 31.4 KHz subcarrier component of the audio multiplex signal mixed in signals a and 8b and the 15.7 KHz horizontal synchronization signal included in the video signal are trapped. At that time, each reactance coil 10 of both trap circuits 8a and 8b is
When a buzz component A is induced in a and 10b, since the winding directions of both reactance coils 10a and 10b are opposite to each other, the polarity of this induced buzz component A is as shown in FIG. 2b. It will be the opposite. Therefore, the output signal of the first trap circuit 10a is L+A, and the output signal of the second trap circuit 10b is R-A. These output signals L+
When A and RA are applied to the transmission matrix circuit 12, the main channel signal taken out from the transmission matrix circuit 12 is (L+A)+(R-A)=
L+R, sub-channel signal is (L+A)-(R-
A)=LR+2A. When the audio multiplexed signal is a stereo broadcast, the FM modulation circuit 14 is set to stereo transmission mode, so the main channel signal L+R and the sub channel signal L-R+2A
and are respectively FM modulated, transmitting antenna 1
Sent from 6.

When this FM broadcast is received by the receiving antenna 18 of the FM receiving circuit 2, this received signal is
The signal is input to the FM demodulation circuit 20, where it is demodulated into a main channel signal L+R and a sub-channel signal L-R+2A. And these signals LR, LR+
When 2A is applied to the receiving matrix circuit 22,
The left audio signal taken out from the reception matrix circuit 22 is (L+R)+(L-R+2A)=2L+2A,
The right audio signal is (L+R)-(L-R+2A)=2R-
It becomes 2A. That is, since the buzz components included in the left and right audio signals have the same level but opposite polarities, as a result, the sound pressure level of the buzz components is audibly lowered during playback.

Furthermore, when the audio multiplexed signal is monaural broadcasting, the FM modulation circuit 14 is set to monaural transmission mode, so only the main channel signals L+R obtained by the transmission matrix circuit 12 are FM-modulated, and then sent to the transmitting antenna. It is transmitted from 16. In this case, the transmitted main channel signal L+R does not contain the buzz component A and also does not contain the stereo pilot signal, so the output of the reception matrix circuit 22 is the main channel signal L+R.
This eliminates the influence of the buzz component induced in the reactance coils 10a, 10b by the external magnetic field.

In this way, the influence of buzz components can be reduced both during FM stereo transmission and monaural transmission.

In this embodiment, a case has been described in which the FM stereo transmitting circuit 1 is built into a TV receiver, but the present invention is not limited to this, and it can also be provided in a VTR or the like.

<Effects of the invention> As described above, according to the invention, the winding directions of the reactance coils constituting the trap circuit are set in opposite directions depending on the left and right audio signals.
Even if a buzz component is induced in the reactance coil by an external magnetic field, the polarity of the buzz component will be reversed between the right audio signal and the left audio signal, resulting in Even if there is, the generation of buzz after FM demodulation can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a block diagram including an FM stereo transmitting circuit according to an embodiment of the present invention, Fig. 2 is an output waveform diagram of a trap circuit including a buzz component generated by the influence of an external magnetic field, and a of the same figure is a diagram of a conventional example. In this case, Figure b shows the case of the present invention. 1...FM stereo transmitting circuit, 2...FM receiving circuit, 8a, 8b...first and second trap circuits,
10a, 10b...Reactance coil, 12...
...Transmission matrix circuit, 14...FM modulation circuit.

Claims (1)

[Claims for Utility Model Registration] Left and right audio signals obtained from a TV receiver, VTR, etc. are passed through a trap circuit consisting of an LC resonant circuit, and then converted into a main channel signal and a sub-channel signal by a transmission matrix circuit. In the FM stereo transmission circuit that modulates and transmits both channel signals, the winding directions of the reactance coils constituting the trap circuit are set in opposite directions depending on the left and right audio signals. Stereo transmission circuit.