JPS60248028A - Service channel signal transmission system - Google Patents

Abstract

PURPOSE:To prevent a demodulation system from giving adverse effects on the reproduction of a main signal by providing a forward AGC circuit acting as AGC operation with high speed response only when an input service channel signal exceeds a prescribed level. CONSTITUTION:The input service channel signal (a) is subjected to full wave rectification 4 and inputted to a comparator 5. A threshold voltage V not overmodulating a transmission local oscillator 2 is fed to the comparator 5, and when the level exceeds the voltage V, a pulse (b) is generated and inputted to a differentiation circuit 6 and an integration circuit 8. A pulse (c) differentiated at the rising/falling of the pulse (b) by the circuit 6 is cut for the differentiated pulse at the falling by a rectifier circuit 7 and the result is inputted to an adder 9. A signal (d) integrated by the circuit 8 is added (9) with an output pulse of the circuit 7 and the result controls a variable again amplifier 11 as a signal (e). On the other hand, the signal (a) is delayed (10) by a delayed part due to an AGC loop, the gain of the amplifier 11 is changed in correspondence to the level change in the input signal, a voice signal overmodulating the oscillator 2 is suppressed immediately and a supervisory signal of a small level is outputted without being clipped.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a digital wireless communication device that modulates a transmitting local oscillator with FM and transmits a service channel signal consisting of an audio signal for a meeting line and a supervisory control signal. This invention relates to improvements in related service channel signal transmission systems.

When transmitting a service channel signal in a digital wireless communication device, a method is often used in which the transmitting local oscillator is FM-modulated with the service channel signal for economical reasons. In this case, the FM modulated wave is converted into a modulated wave. It is desirable that the service channel signal be satisfactorily reproduced on the receiving side without adversely affecting the main signal consisting of a phase-shifted 1111a (PSK) wave signal.

[Conventional technology]

FIG. 4 is a block diagram of a conventional service channel signal transmission system, in which 1 is a frequency converter that converts the main signal in the intermediate frequency band to a radio frequency band, and 2 is a frequency converter for converting the frequency in the frequency converter 1. The transmitting local oscillator 3 is a backward feedback A (, C or limiter) provided at the input of the signal.

The conventional transmitting local oscillator 2 is set to F by the service channel signal.
When transmitting with M modulation, a backward feedback AGC or limiter 3 is provided at the input of the service channel signal to prevent the transmitting local oscillator 2 from being overmodulated.

However, when the backward feedback AGC 3 is installed, if a large audio signal is suddenly input, the backward feedback AGC 3 will not be able to follow it, and a high level signal will be input to the transmitting local oscillator 2, resulting in an over-variable signal, which will cause the demodulation system to There is a problem in that it has an adverse effect on the reproduction of the digital signal, and when the limiter 3 is provided, the audio signal for the meeting line and the supervisory control signal are multiplexed, as shown in FIG. 5(A). When the audio signal becomes large, it is limited so that it does not become over-transformed, but as shown in Figure 5 (B), the low-level monitoring control signal is clipped, and this clipped part cannot be reproduced on the receiving side. There is.

[Problem that the invention seeks to solve]

As explained above (in the conventional service channel signal transmission system, when backward feedback AGC is used, there is a problem that if a sudden loud voice is input, it does not adversely affect the reproduction of the main digital signal in the demodulation system. However, when a limiter is used, there is a problem that when the audio signal becomes large, the low-level monitoring control signal is clipped, and the clipped portion cannot be reproduced on the receiving side.

[Means for solving problems]

The above problem is solved by the service channel signal transmission system of the present invention, which includes a forward feedback AGC circuit that performs a high-speed response AGC operation only when the service channel signal exceeds a predetermined level. .

[Effect]

In the case of the present invention, if the audio suddenly becomes louder, the gain is immediately lowered by the fast-response forward feedback AGC circuit, so no large level signal appears on the output side, and the transmitting local oscillator does not overmodulate. , there will be no adverse effect on the reproduction of the main digital signal in the demodulation system, and even if a low-level supervisory control signal is superimposed, it will not be clipped and its gain will be compressed and passed through. It can be played back on the receiving side.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Fig. 1 is a block diagram of a service channel signal transmission system according to an embodiment of the present invention, Fig. 2 is a time chart of waveforms of each part in Fig. 1, and (A) to (E) are points a to e in Fig. 1. (F) shows the gain change, and in the figure, 10 is a delay circuit and 11 is a variable gain amplifier. For the purpose of the present invention, the same reference numerals indicate the same functions.

In FIG. 1, the input signal shown in FIG. 2(A) is full-wave rectified by a full-wave rectifier circuit 4 and input to a comparator 5. A threshold voltage V is applied to the comparator 5 so that the transmitting local oscillator 2 does not become overmodulated.
A pulse as shown in Figure (B) is emitted.

This pulse is input to a differentiating circuit 6, which outputs differentiated pulses at the rising and falling points as shown in FIG. Enter 9.

On the other hand, the output pulse of the comparator 5 is also input to an integrating circuit 8 and is integrated to become a pulse as shown in FIG. 2(D) and input to an adder 9.

The adder 9 adds the two, and the result is as shown in FIG. 2(E).
For the rising edge, a high-speed response pulse is formed by the differentiating circuit 6, and in addition to the variable gain amplifier 11, the pulse is
Change the gain as shown in .

- The universal power signal is delayed by the delay caused by the AGC loop in the delay circuit 10 and inputted to the variable gain amplifier 11, so that the variable gain amplifier 11 responds to changes in the level of the input signal.
Since the gain changes of the transmitting local oscillator 2 are synchronized, a large audio signal that causes overmodulation of the transmitting local oscillator 2 is immediately suppressed, and a superimposed small level supervisory control signal is compressed and passed.

Therefore, the transmitting local oscillator 2 will not be overmodulated and will not have a negative effect on the reproduction of the main signal digital signal in the demodulation system, and even if a low-level supervisory control signal is superimposed, it will not be clipped. Since the ★1j gain is compressed and passed through, it will not become unplayable on the receiving side.

FIG. 3(A) is a perspective view of another embodiment of the present invention.
FIG. 3(B) is a characteristic diagram of the window type comparator.

In the figure, 12 indicates a window type comparator.

The difference between FIG. 3 and FIG. 1 is that a window type comparator 12 is used instead of the full-wave rectifier circuit 4 and comparator 5.

The characteristics of this window type comparator 12 are as shown in FIG. When the voltage exceeds 1, a Lebel pulse is generated, and a single window type comparator 12 performs the operations of the full-wave rectifier circuit 4 and the comparator 5 shown in FIG.

Therefore, the operation in the case of FIG. 3(A) is the same as in the case of FIG.

〔Effect of the invention〕

As described in detail above, according to the present invention, even if a loud voice is suddenly input, it will not have an adverse effect on the reproduction of the main signal digital signal in the demodulation system, and a low level supervisory control signal will not be superimposed. Even if the signal is recorded, it is not clipped and the gain is compressed and passed through, which has the effect of eliminating problems that cannot be reproduced on the receiving side.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a service channel signal transmission system according to an embodiment of the present invention, FIG. 2 is a time chart of waveforms of each part in FIG. 1, and FIG. Block diagram: Figure 3 (B) is a characteristic diagram of the window comparator; Figure 4 is a block diagram of a conventional service channel signal transmission system; Figure 5 is a multiplexing of voice signals and supervisory control signals for the meeting line. FIG. In the figure, ] is a frequency converter, 2 is a transmitting local oscillator, 3 is a backward feedback AGC or limiter, 4 is a full-wave rectifier circuit, 5 is a comparator, 6 is a differentiator circuit, 7 is a rectifier circuit, 8 is an integration circuit, 9 is an adder, 10 is a delay circuit, 11 is a variable gain amplifier, and ]2 is a window comparator. Agent Patent Attorney Hiroshi Matsuoka

Claims (1)

[Claims] In a digital wireless communication device that FM-modulates a transmitting local oscillator with a service channel signal and transmits the signal, forward feedback performs AGC operation with a commercial speed response only when the service channel signal exceeds a predetermined level at the input of the service channel signal. A service channel signal transmission system characterized by providing an AGC circuit.