JPS5970038A - Fm transmitting/receiving system - Google Patents

Abstract

PURPOSE:To expand the band of a voice signal by removing a tone signal by a signal synthesizing means. CONSTITUTION:An FM interphone adopting a tone type transmitting/receiving system has a transmitting system 2 and a receiving system 4. A voice signal S and a tone signal St are added by an adder 10 and FM-modulated and the modulated signal is sent to a lamp line 16. The received FM signal is demodulated by a demodulating circuit 20. A tone signal detecting circuit 22 takes out a tone signal from the demodulated signal. A waveform converting circuit 26 converts the waveform of a tone signal St into its reverse phase. The inverted tone signal -St is inputted to a signal synthesizing circuit 28. The circuit 28 adds the demodulated signal to the inverted tone signal -St and extracts the tone signal St component from the demodulated signal. Consequently, a normal voice signal is obtained. Since the signal synthesizing technique is adopted, a filter can be omitted and the system is reduced in size and produced unexpensively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM transmitting/receiving system, and particularly to an improvement of a suitable transmitting/receiving system such as a tone-based FM telephone.

Generally, FM telephones include a breathtalk system, a simultaneous call system, and a tone system. As is well known, the press daughter method is a wired transmitting and receiving system that performs transmission and reception by pressing a push button, and this method has the drawback that the push button must be operated each time transmission and reception are performed. - Also, the simultaneous call system is a system in which the transmitting and receiving frequencies are different, and both signals are sent and received at the same time. Since this method uses different frequencies, it is necessary to set the frequency bands of both waves apart by a certain range, for example, about 40 K fiz, in order to avoid interference between transmission and reception. For this reason, this method requires a large number of frequency allocations, and has drawbacks such as the number of lines being limited by frequency allocation.

On the other hand, the tone method does not have the drawbacks of the above-mentioned methods, and by varying the tone frequency with respect to the number of carrier frequencies set, many lines can be formed, and the frequency band of the audio signal can be relatively wide. Therefore, it is suitable for music broadcasting as well as omnipotent broadcasting systems for buildings, schools, etc.

However, in conventional tone-based FM transmitting and receiving systems, methods such as outputting the tone signal together with the audio signal or removing the tone signal at the output stage are adopted. When a tone signal is output together with an audio signal, there is a drawback that the audio signal band is limited in order to avoid the influence of the tone signal. Furthermore, when a tone signal set to a low frequency is removed by a filter, the audio band becomes wider, but since the low frequency tone signal is removed, the filter becomes large and the system becomes expensive.

This invention aims to expand the audio signal band by removing the tone signal component from a tone composite signal obtained by combining a tone signal and an audio signal through signal synthesis, and also aims to expand the audio signal band by eliminating the need for a conventional removal filter. The purpose is to provide an FM transmitting and receiving system based on the following methods.

Embodiments of the invention will be described in detail with reference to the drawings. 1 and 2 show an embodiment of the F'M transmission/reception system of the present invention, FIG. 1 showing the FM transmission/reception system, and FIG. 2 showing a tone signal detection circuit. In the figure, a transmitting system 2 and a receiving system 4 are installed in this transmitting/receiving system.

The transmission system 2 includes an adder circuit 10 that adds the audio signal S given from the signal source 6 and the tone signal St given from the signal source 8, and an FM modulation circuit 12 that frequency-modulates a carrier wave with the output of the adder circuit 10. is installed. That is, a tone synthesized signal So obtained by synthesizing the tone signal St with the audio signal S formed by addition in the adding circuit 10 is input to the FM modulation circuit 12. This FM modulation circuit 12 is supplied with a carrier wave f from a signal source 14, this carrier wave r is frequency modulated by the tone composite signal So, and the modulated output signal is sent to an electrolytic wire 16 serving as a transmission medium.

On the other hand, the signal sent to the electrolytic wire 16 is transmitted to the receiving system 4
is received via the electrolytic wire 16. A high frequency amplification circuit 18 for amplifying the received modulated input signal is installed at the input stage of the reception system 4, and the amplified output is demodulated by the FM demodulation circuit 20 at the next stage so that the tone composite signal is extracted. It is made.

This tone composite signal so is input to a tone signal detection circuit 22 and an audio signal detection circuit 24, which constitute a tone cancellation circuit that removes the tone signal and extracts the audio signal. The tone signal detection circuit 22 is a circuit that detects a tone signal in a composite signal, and is a circuit that detects a tone signal in a composite signal.
(locked 1oop ) circuit. The audio signal detection circuit 24 also includes the tone signal detection circuit 2.
This is a circuit that synthesizes the tone signal detected in step 2 and the composite signal to extract an audio signal, and this audio signal detection circuit 2
4 includes a waveform conversion circuit 26 that converts the tone signal supplied from the tone signal detection circuit 22 to form an inverted tone signal 1τ having a sin waveform and having an opposite phase to the detected tone signal; and an output of this waveform conversion circuit 26. a signal synthesis circuit 28 that synthesizes the inverted tone signal having a waveform and the tone synthesis signal;
is installed.

An output amplifier 3° for amplifying the extracted audio signal is installed on the output side of the audio signal detection circuit 24, and its amplified output is input to the speaker 32.

Further, a tuning display circuit 34 is installed on the output side of the tone signal detection circuit 22, and the tuning display circuit 34 is configured to display the tuning state with a display element such as a light emitting diode based on the tone signal output. .

With the above configuration, the modulated output signal sent from the transmission system 2 to the molten wire 16 is received by the reception system 4. The received signal is amplified by the high frequency amplification circuit 18, and then demodulated by the FM demodulation circuit 2o, and a tone composite signal So is detected. This tone composite signal So is input to the tone signal detection circuit 22 to extract the tone signal St, and this tone signal S+t is applied to the waveform conversion circuit 26 of the audio signal detection circuit 24. The waveform conversion circuit 26 converts the waveform of the detected tone signal St to form an inverted tone signal of a sine waveform having an opposite phase to the detected tone signal St. This inverted tone signal 1T is input to the signal synthesis circuit 28 together with the tone synthesis signal So, and only the audio signal S is extracted from the tone synthesis signal So by signal synthesis by addition and subtraction of both signals. This audio signal S is amplified by an output amplifier 30 and then given to a speaker 32, and the speaker 32 is driven by this audio input.

On the other hand, the output of the tone signal detection circuit 22 is output from the tuning display circuit 3.
4 and indicates that the signal is tuned to a predetermined received signal.

According to such a system, only the audio signal can be extracted from the tone composite signal by means of signal synthesis. Therefore, the frequency band of the reproduced signal can be expanded, and a broadcasting system that emphasizes sound quality, such as music broadcasting, can be configured.

Furthermore, since tone signals are removed by signal synthesis, there is no need for a removal filter like in the past, making the system smaller and cheaper.

For example, a system can be configured by setting 300 Ilz to 30 Kllz as the voice band and 5011z to 20011z or 5KIIz to 1QKIlz as the tone signal band. In other words, even if a tone signal band is selected within the voice band, the tone signal is removed by combining the signal components, so unlike the case of conventional filters, the tone signal does not affect the voice signal. Signals can be removed efficiently.

In addition, since signal synthesis is performed by addition and subtraction using sine waveforms,
It is possible to avoid adverse effects such as spurious interference due to high-order harmonic components.

FIG. 2 shows a specific configuration of the tone signal detection circuit 22. As shown in FIG. This tone signal detection circuit 22 has PLL
(phase'1ocked 1oop) circuit. That is, the tone composite signal So applied to the long sword terminal 36 is input to the phase comparator 38 together with the feedback signal, and a phase shift is detected. The output of this phase comparator 38 is input to a voltage controlled oscillator 42 via a low pass filter 4o. The voltage controlled oscillator 42 is a low pass filter 4o
In response to a control input applied through the oscilloscope, a signal having a frequency proportional to the voltage value is generated, and the output of this oscillation is fed back to the phase comparator 38 as a comparison input. Further, the tone signal St generated by the voltage controlled oscillator 42 is taken out from the output terminal 44 and inputted together with the tone composite signal SO to the phase comparator 46 of the tuning display system. The comparison output of this phase comparator 46 is input to an amplifier 50 via a low-pass filter 48, and the amplified output is taken out from an output terminal 52.

The tone signal St taken out from the output terminal 44 is input to the waveform conversion circuit 26 of the audio signal detection circuit 24, and on the other hand,
The tone signal St generated at the output terminal 52 is input to the tuning display circuit 34.

By configuring the tone signal detection circuit 22 in this manner, the tone signal St can be extracted from the tone composite signal So with high precision and in a stable state. In particular, in this embodiment, tone signals for displaying tuning can be detected at the same time, and the circuit configuration can be simplified.

In the embodiment, one transmission system 2 and one reception system 4 have been described, but in an actual system, a plurality of reception systems 4 are installed for one transmission system 2, or a pair of transmission system 2 and reception system 4 are installed. The system 4 is installed in each room, etc., and constitutes a broadcasting system or an intercom.

As explained above, according to the present invention, only the audio signal is extracted from the tone composite signal by signal synthesis, so it is possible to widen the audio band, eliminate the need for a filter for tone signal removal, and make the system cheaper. It can be configured as follows.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a transmitting/receiving system of the present invention, and FIG. 2 is a block diagram showing an embodiment of a tone signal detection circuit. 20...FM demodulation circuit, 22...Tone signal detection circuit, 24...Audio signal detection circuit.

Claims (1)

[Claims] FM that combines a tone signal with a voice signal to form a tone composite signal and uses this tone composite signal as a modulation signal.
In an FM transmitting/receiving system having a transmitting system for transmitting a signal and a receiving system for receiving an FM signal given from the transmitting system, an FM demodulating circuit demodulating a tone composite signal from the FM signal; A tone signal detection circuit is provided with a tone composite signal and detects the tone signal in the composite signal;
An FM transmitting/receiving system comprising: an audio signal detection circuit that synthesizes the tone synthesis signal provided from the demodulation circuit to extract an audio signal.