JP2591142B2 - Composite modulation transmission system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] An intermediate relay station B combines a monitor / conference telephone signal received from a preceding station A together with a main signal and demodulated with a monitor / conference telephone signal, and combines the monitor signal and the conference telephone signal. Regarding the composite modulation transmission system in which the main signal of digital modulation is modulated by the FM modulator with the combined output and the composite modulation signal of digital modulation and FM modulation is transmitted to the next station C. For the purpose of a composite modulation transmission method in which the FM deviation of the terminal relay station is set to a certain value or less and no error occurs in the monitoring signal at the last terminal relay station, the intermediate relay station sends its own meeting telephone signal to the FM modulator. A variable attenuator that adjusts the level of the signal to be adjusted, a superimposing device that superimposes the supervisory signal of the own station on the output of the variable attenuator, and a monitoring / meeting telephone signal received from the preceding station are synthesized with the output of the superimposing device.
A synthesizer for sending to the FM modulator and a detection circuit for detecting a part of the synthesized output and holding a peak value of the detection output, and controlling an attenuation amount of the variable attenuator by the peak value held by the detection circuit. The transmission level of the meeting telephone signal is limited, but the level of the monitor signal is not controlled, and the FM shift amount of the FM modulation signal due to the output of the synthesizer is maintained at a certain value or less.

[Industrial applications]

The present invention relates to digital multiplex radio, and more particularly to a composite modulation transmission system for digitally modulating a main signal and FM-modulating an auxiliary signal monitoring signal or a meeting telephone signal for transmission.

[Conventional technology]

This composite modulation transmission system, as shown in Figure 5, the monitoring is received from the previous position station A at an intermediate relay station B demodulates-meeting telephone signal SV _O, the OW _O, monitor and meetings telephone signal SV of the own station , OW
The synthesized in the hybrid H ₁ for example, a transmission local oscillator 10 _A
Is FM-modulated, the frequency of the digitally modulated IF main signal is converted to microwaves, and the resultant signal is transmitted to the next station C as a composite modulation signal of digital modulation and FM modulation.

Therefore monitoring is input to the FM modulator 10 _A of the intermediate repeater station,
The composite level of the meeting telephone signal increases as the number of intermediate relay stations A placed in front increases, and the amount of FM deviation for FM-modulating the main signal increases. The influence of the modulation on the transmission quality of the main signal increases. In particular, the level of the meeting telephone signal OW may generally rise from the test sound level of the standard setting to about 12 dB, so that when using the meeting telephone at each station at the same time, the effect is large. Conventionally as a method for suppressing an increase in the FM deviation of the FM modulator 10 _A of the intermediate repeater station, as Figure 6,
Place the limiter 1A in front of the FM modulator 10 _A, but the amplitude of the monitor and meeting telephone signal input and a method of FM modulation then restricted with limiter 1A, monitoring and meeting telephone signal SV input limiter 1A, OW When the level is high, the level of the monitor signal SV also decreases at the output of the limiter 1A, and therefore, there is a disadvantage that an error occurs in the monitor signal at the last terminal relay station (not shown).

[Problems to be solved by the invention]

The present invention relates to monitoring and meeting telephone signals of each intermediate relay station.
Automatically control the FM deviation of the modulation signal to a certain value or less,
It is an object of the present invention to provide a composite modulation transmission system that does not cause an error in a monitoring signal at a terminal relay station at the end.

[Means for solving the problem]

As shown in the principle diagram of FIG. 1, the problem is that the intermediate relay station B performs FM modulation of the meeting telephone signal OW of its own station.
Variable attenuator 1 for adjusting the transmission level to the transmitter, a superimposer 2 for superimposing a supervisory signal SV of the output of the variable attenuator on its own station, and monitoring / meeting received from the preceding station A on the output of the superimposer. Telephone signal SV _O. A synthesizer 3 synthesizes the OW _O sends a synthesized output OUT to the FM modulator 10, a detection circuit 4 for holding a peak value V _p of detects the partially detection output of the output OUT of the combiner comprises, controlling the attenuation amount of the variable attenuator 1 a peak value V _p for holding the detection circuit 4 as a control signal, the self beak of the output OUT of the combiner 3 is increased attenuation of the variable attenuator 1 it exceeds a certain value An automatic gain control circuit is configured to reduce the transmission level of the office meeting telephone signal OW so as to keep the peak value of the combined output OUT of the combiner 3 at a certain level or less, and to output the FM modulator with a fixed FM deviation amount. Is transmitted to the next station C.

In the principle diagram of FIG. 1 showing the configuration of the composite modulation transmission system of the present invention, reference numeral 10 denotes a supervised / meeting telephone signal SV _O. OW _O is combined with the monitoring signal SV of the own station and the meeting telephone signal OW, and the combined output OUT
A composite modulation transmission system in which the local oscillator of the main signal is FM-modulated, the frequency of the digitally modulated intermediate frequency IF main signal is converted to microwaves, and transmitted to the next station C as a composite modulation signal of digital modulation and FM modulation This is the FM modulator of the intermediate relay station.

Reference numeral 1 denotes a variable attenuator that adjusts the level of a meeting telephone signal OW of the own station to be transmitted to the FM modulator 10 by a control signal.

Reference numeral 2 denotes a superimposer for superimposing the monitoring signal SV of the own station on the output of the variable attenuator 1.

3 is a monitor / meeting telephone signal SV _O. OW _O is combined and combined output OU
This is a synthesizer that sends T to the FM modulator 10.

4 is a detection circuit for holding a predetermined time the peak value V _p of branches a part detection to detection output of the output OUT of the combiner 3.

Then it controls the variable attenuator 1 a peak value V _p for holding the detection circuit 4 as a control signal, synthesizer third output OUT level of the own station to increase the attenuation amount of the variable attenuator 1 it exceeds a certain value of An automatic gain control circuit is configured to reduce the transmission level of the meeting telephone signal OW so as to keep the peak value of the output OUT of the synthesizer 3 at a constant level.

[Action]

The variable attenuator 1 adjusts the level of the meeting telephone signal OW of its own station to be sent to the FM modulator 10 by a control signal and supplies the adjusted signal to the superimposing device 2.

The superimposing device 2 outputs the monitoring signal SV of its own station to the output of the variable attenuator 1.
Are superimposed and sent to the synthesizer 3.

The synthesizer 3 receives the demodulated monitoring / meeting telephone signal SV _O. OW _O is combined and the combined output OUT is sent out to the FM modulator 10.

Detection circuit 4, the output OUT of the combiner 3 branched by detecting a part to hold the peak value V _p of the detection level, and supplies a control signal the peak value V _p which holds the variable attenuator 1.

The variable attenuator 1 controls the amount of attenuation to the peak value V _p for holding the detection circuit 4 as a control signal, the synthesizer 3
When the peak value of the output OUT exceeds a constant value, the attenuation of the variable attenuator 1 is increased, the transmission level of the meeting telephone signal OW of the own station is reduced, and the peak value of the output OUT of the synthesizer 3 is kept at a constant level. The FM modulator 10 that FM-modulates the main signal of the digital modulation by the output OUT of the combiner 3 outputs the output OU of the combiner 3.
Since the peak value of T is kept at a constant level, the FM shift amount of the FM modulation is equal to or less than the constant value. Therefore, according to the composite modulation transmission system of the present invention, the level of the meeting telephone signal among the monitoring / meeting telephone signals at each intermediate relay station is limited, but the level of the monitoring signal is not limited. Since the peak value of the combined output is FM-modulated while being kept constant, no error occurs in the monitor signal transmitted to the final terminal relay station, and the problem is solved.

〔Example〕

FIG. 2 is a table showing specifications of monitoring / meeting telephone signals of each station showing the configuration of the composite modulation transmission system according to the embodiment of the present invention.
FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is a circuit diagram of a variable attenuator 1 of an automatic gain control circuit for monitoring / meeting telephone signals of each intermediate relay station, and FIG. 2 (b) is a circuit diagram of a detection circuit 4. FIG. 4 is a waveform chart for explaining the operation of the embodiment of the present invention.

The specification table of FIG. 2 shows the case where the composite modulation transmission system comprises five stations A to E. When each of the stations A to D uses a meeting telephone at the same time, the station D of the intermediate relay station is used. The FM shift amount of the FM modulation is proportional to the sum of the voltages of the transmission levels of the stations A to D.
Now, let the FM deviation for each station's test sound be 50KHz rms,
Assume that the proof strength of the demodulator DEM of the last station E is 500 KHz rms.

When the peak value of the transmission level of the meeting telephone signal of each station is 10 dB higher than the test sound, the maximum deviation is 160 KHz at station A.
The rms, B station is 320 KHz rms, C station is 480 rms, and D station is 640 KHz rms, which exceeds the 500 KHz rms tolerance of the demodulator DEM of the E station.

Here, monitoring and monitoring of each station using the automatic gain control circuit of the present invention are described.
Set the peak value of the combined output of the meeting telephone signal to 160KHz rms at station A, 270KHz rms at station B, 390rms at station C, and 500K at station D.
The Hz rms is set so that the maximum FM shift amount of the FM modulation by the combined output at the station D does not exceed the tolerance of the demodulator DEM of the station E of 500 KHz rms.

Variable attenuator 1 of the automatic gain control circuit of the present invention, as the circuit diagram of FIG. 3 (a), a diode D ₁ and a resistor R ₁ as main components, impedance current flows through the diode D ₁ There are those caused attenuation by reducing, resistor R ₁ is intended to limit the current flowing through the diode D _1. Capacitors C ₁ and C ₂ are used to cut a DC bias applied to diode D ₁ .

The detection circuit 4 in (b) of the circuit diagram of FIG.
D ₁ and to D ₄ and the full-wave rectifier circuit constituted by a resistor R ₁ to R ₄ and amplifier OPAmp _1, by the diode D ₅ and the capacitor C ₁ and the amplifier OPAmp ₂ and the variable resistor RV ₁ and a resistor R ₅ And a peak hold circuit. One of the combined output OUT of the monitor / conference telephone signal (FIG. 4 (a)) from the preceding station and the monitor / conference telephone signal (FIG. 4 (b)) from the own station in the combiner 3 (not shown). Branch and diode D
The ₁ to D ₄ for full-wave rectification. And after rectification, the amplifier opAMP
By performing differential amplification by _1, a full-wave rectified waveform of the above two signals ((c) in FIG. 4) is input to the peak hold circuit. The time constant tau of the charging and discharging of the peak hold, the determined tau = C ₁ · R ₅ by a resistor R ₅ and capacitor C _1. Variable resistor RV ₁ is an offset voltage is applied to OPAmp _2, detection input, as in the fourth diagram of (d) the peak hold output waveform,
When the voltage exceeds a certain offset voltage value, a positive voltage Vp is output. The variable attenuator 1 is driven by using the positive voltage Vp as a control signal, and the amount of the attenuation is changed as shown in FIG. Keep the peak value constant.

Accordingly, in the composite modulation transmission system of the embodiment shown in FIG. 2, the level of the conference telephone signal among the monitored and conference telephone signals at the intermediate relay stations B, C and D is automatically limited by the variable attenuator 1. However, the level of the supervisory signal is not directly controlled. However, since the peak value of the combined output of the meeting telephone signal and the supervisory signal is kept constant and FM-modulated, the supervisory signal transmitted to the final station E and demodulated is transmitted. There is no problem with no errors.

〔The invention's effect〕

As described above, according to the present invention, the level of the meeting telephone signal is automatically limited at each intermediate relay station, but the level of the monitoring signal is not directly controlled, but the combined output of the meeting telephone signal and the monitoring signal is output. FM peak value is kept constant
Since the signal is modulated, no error occurs in the monitoring signal transmitted to the final terminal station and demodulated to monitor the state of each station, and the effect of improving the reliability of the remote monitoring of the wireless transmission system can be obtained.

[Brief description of the drawings]

FIG. 1 is a principle diagram showing a basic configuration of a composite modulation transmission system according to the present invention. FIG. 2 is a specification table of monitoring / meeting telephone signals of respective stations showing a configuration of a composite modulation transmission system according to an embodiment of the present invention. FIG. 3 is a circuit diagram of an automatic gain control circuit for monitoring / meeting telephone signals according to the embodiment of the present invention. FIG. 4 is a waveform diagram for explaining the operation of the embodiment of the present invention. FIG. 6 is a block diagram of an FM shift suppressing circuit of the conventional composite modulation transmission system. In the figure, 1 is a variable attenuator, 2 is a superimposer, 3 is a combiner, 4 is a detection circuit, and 10 is an FM modulator.

Claims (1)

(57) [Claims] An intermediate relay station B combines a monitor / conference telephone signal received and demodulated together with a main signal from a preceding station A with a supervisory signal of the own station and a conference telephone signal, and a digital signal is output from the composite output. In a composite modulation transmission system in which a main signal of modulation is modulated by an FM modulator and a composite modulation signal of digital modulation and FM modulation is transmitted to the next station C, the intermediate relay station B converts the meeting telephone signal of the own station into the FM. A variable attenuator (1) for adjusting the level to be sent to the modulator (10), a superimposer (2) for superimposing a monitor signal of the own station on an output of the variable attenuator, and a preceding station A at an output of the superimposer. Monitoring received from
A synthesizer (3) for synthesizing the meeting telephone signal and sending it to the FM modulator; and a detection circuit (4) for detecting a part of the synthesized output and holding a peak value of the detection output. ) Controls the amount of attenuation of the variable attenuator (1) by controlling the peak value held therein, thereby limiting the transmission level of the meeting telephone signal, but without controlling the level of the monitoring signal.
A composite modulation transmission system characterized in that the FM deviation of the FM modulation signal due to the combined output of the signals is kept below a certain value.