JPS6135079A - Receiver of sound multiplex broadcast - Google Patents

Abstract

PURPOSE:To accomplish the identification of a noise and to discriminate properly the presence or absence of sound multiplex broadcast by carring out the on or off control of a switch circuit with use of a tuning circuit for tuning to a horizontal scan frequency and a frequency integer-times the former except the frequency of a subchannel signal. CONSTITUTION:Outputs of a sound intermediate frequency amplifier and detector circuit 1 of a sound multiplex brodcast receiver are applied to a subchannel demodulator circuit 2 and detection circuit 5, and a multiple signal of subchannel is demodulated by the circuit 2. The multiple signal from the circuit 2 is applied to a squelch circuit 3 and a detection circuit 6. The output for tuning to a subchannel carrier overlapped with a main channel feom the detection circuit 5 and that from the detection circuit 6, which tunes to a frequency for convering a horizontal scan frequency except the sub-channel signal and a frequency integer-times the former, are decided by a deciding circuit 7. It decides the absence of either of the signals. When no signal is found in addition to the judgement of no subchannel carrier, the circuit 3 is controlled off or on, and the presence or absence of sound multiplex broadcast is properly discriminated.

Description

[Detailed Description of the Invention] [Field for iF+1 of the Invention] The present invention is an audio multiplex broadcasting receiver equipped with an audio multiplex demodulation circuit, and in particular detects an audio multiplex signal using the FM method for modulation of sub-channels. The present invention relates to an audio multiplex broadcasting receiver for use in broadcasting.

[Background of the invention]

In the audio multiplex broadcasting system, as shown in the November 207B issue of Choshibi Techniques, generally a subcarrier is used as a subcarrier in order to carry another audio signal (subchannel signal) on the main membrane transmission. channel, and combine this with a conventional audio signal (
The FM-FM method uses a method of combining the main channel signal) and modulating the main carrier wave with this, and uses the EM method for modulating the sub channel.

An AM-FM method using AM method 4 is used. .

In the special KFM-F'M method, in order to reduce the effect of audio buzz, the sub-channel carrier wave is set at the horizontal scanning frequency or its integer, since the buzz components are concentrated around the horizontal scanning frequency and its harmonics. A method of selecting twice as many is used.

In addition, as a method for determining whether or not an audio multiplexed signal is being broadcast, in order to reduce the influence of audio buzz components, the determination signal is transmitted between the horizontal scanning frequency and an integer multiple thereof (for example, 5.5 times the horizontal scanning frequency). etc.).

However, on November 9, 1981, the National
Association of Broadcaste
rs issue'Mult i Channel LTel
As shown in EVITION 5ound' VOL 1-A, audio multiplex broadcasting system where there is no discrimination signal % type % In such a case, the secondary channel is set when the electric field is 1 weak or when the reception condition is poor and there is a lot of buzzing sound. It was difficult to determine the carrier wave without malfunction.

[Purpose of the invention]

The present invention eliminates the drawbacks of the prior art described above.

To provide an audio multiplex broadcast receiver for determining the presence or absence of audio multiplex broadcast without malfunction.

[Summary of the invention]

The present invention provides a tuning circuit connected to the audio intermediate frequency detection output and tuned to the sub-channel carrier wave, and a tuning circuit connected to the output of the sub-channel demodulation circuit, and which is connected to the output of the sub-channel signal and has a frequency between the horizontal scanning frequency and an integral multiple thereof. A tuning circuit tuned to the carrier wave and noise level turns on/off the squelch circuit that mutes on when there is no signal.

[Embodiments of the invention]

The figure is a schematic diagram showing an embodiment of a sub-channel demodulation circuit according to the present invention.

1 is an audio intermediate frequency-width/detection circuit, 2 is a sub-channel demodulation circuit, 3 is a squelch circuit that mutes the sub-channel signal when it is not being transmitted, 4 is a demodulated signal output terminal, and 5 is an audio intermediate frequency amplification circuit.・Detection circuit 6 extracts the sub-channel carrier wave from the output of the detection circuit 1, detects it with the detection circuit, and determines that there is a carrier wave when the DC voltage is above a certain voltage, and that there is no carrier wave when the DC voltage is below a certain voltage. 5.5 fm (/
H: horizontal carrier frequency), extracts the noise component with a spectral distribution centered on 3.57H, detects it with a detection circuit, and when the DC voltage is above a certain voltage, there is no carrier wave, and a certain certain voltage In the above cases, a detection circuit determines that there is a carrier wave, and 7 is a determination circuit that outputs a signal that operates the squelch circuit 5 when it is determined that there is no carrier wave, based on the outputs of the detection circuit 5 and the detection circuit 6. It is.

Under normal reception conditions, the audio intermediate frequency amplification/detection circuit 1 outputs a signal in which the subchannel/I/signal is superimposed on the main channel audio, and the subchannel demodulation circuit 3 demodulates the multiplexed signal. Ru. At this time, only a slight residual noise component is output in the vicinity of the 5.5 fH frequency in the output of the sub-channel demodulation circuit 5, and the detection circuit 6 determines that a carrier wave is present.

Further, the output of the detection circuit 5 is similarly determined to be a carrier wave cloth, and normal operation can be performed.

Next, when the sub-channel signal is cut off, large noise peculiar to FM detection occurs in the output of the sub-channel demodulation circuit, and the detection circuit 6 determines that there is no carrier wave. Similarly, since there is no sub-channel carrier wave, the detection circuit 5 also determines that there is no carrier wave.

At this time, since the detection circuit 5 generally has a shorter response time, it is possible to reduce noise when the signal is cut off.

In addition, when the buzz component increases in the audio detection output, the detection circuit 5 may determine that there is a carrier wave even when there is no carrier wave.In this case, only noise is output from the subchannel demodulation circuit 6. Since it is determined that there is no carrier wave, the detection circuit 6 determines that there is no carrier wave as a whole.

Further, in the case of no signal, noise components increase in the output of the audio intermediate frequency amplification/detection circuit 1, and the 87N of the signal deteriorates. At this time, the detection circuit 5 mistakes the noise for a carrier wave, so it is determined that there is a carrier wave cloth even when there is no carrier wave, but the detection circuit 6 determines that there is no carrier wave as the noise increases, so the overall It is determined that there is no carrier wave.

Furthermore, even if there is a residual carrier wave leaked from the output of the sub-channel demodulation circuit 2, the detection circuit 6 can identify it as noise.

〔Effect of the invention〕

As described above, according to the present invention, the presence or absence of a signal on a sub-channel can be determined without malfunction even in a weak electric field.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a sub-channel demodulation circuit according to the present invention. 1...Audio intermediate frequency amplification/detection circuit, 2...
...Subchannel demodulation circuit. 3... Squelch circuit, 5.6... Detection circuit, 7... Judgment circuit.

Claims (1)

[Claims] An audio multiplex broadcasting system in which an FM-modulated sub-channel carrier wave superimposed on a main channel signal is selected to have a horizontal scanning frequency or an integral multiple thereof, comprising: an audio-visual detection circuit;
An audio multiplex broadcasting receiver comprising an audio intermediate frequency amplification and detection circuit supplied with the detection output thereof and an audio multiplex signal demodulation circuit supplied with the output of the audio intermediate frequency amplification and detection circuit, the audio intermediate frequency amplification and detection circuit comprising: a first detection circuit which is supplied with the output of the circuit and tunes to the sub-channel carrier wave superimposed on the main channel signal and detects the output to obtain a side output; a second detection circuit that tunes to a frequency other than the channel signal between the horizontal scanning frequency and an integral multiple thereof, and detects the output thereof to obtain a detection output; Audio multiplex broadcast reception characterized by controlling the on/off, etc. of a squelch circuit that determines that there is no sub-channel carrier wave when any one outputs a no-signal state, and turns on/off a squelch circuit when there is no signal. Machine.