JPH0447837A - Automatic frequency control system - Google Patents

Abstract

PURPOSE:To shorten pull-in time by sharply reducing a common frequency fluctuating component in a signal propagation path by inputting an AFC signal from a demodulator in a synchronized state to the other demodulator in an asynchronous state, and moving the operational voltage. CONSTITUTION:An N kinds of modulated signals 21A-23A passed through the same signal propagation path are inputted to the demodulator and demodulated by a reproduced carrier signal. However, assuming that a demodulator 21 is set in the synchronous state and other demodulators 22 and 23N are set in the asynchronous state, the central voltage of an AFC signal 21B from the demodulator 21A in the synchronous state is transmitted to a controller 5 and stored. Further, the controller 5 transmits the central voltage of this AFC signal 21B to an AFC circuit 3B or the like of the other demodulator as AFC signals 22B and 23B and moves the operating point so as to obtain the same voltage as this central voltage. Thus, since moving to a state close to AFC pull-in by such a control operation, AFC sweeping width can be turned to the synchronous state with narrow sweeping width.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic frequency control system, and in particular, to a system that includes a plurality of demodulators and a control device that controls and monitors these demodulators. Automatic frequency control system that receives and passes AFC information between the demodulator and the control device to achieve synchronization [Prior art] The conventional automatic frequency control system uses AFC for carrier synchronization.
As for the circuit, an independent A
It was equipped with an FC lead-in sweep circuit, and the control device only monitored the AFC information of each demodulator. In the past, even if there was a common frequency fluctuation with the same tendency due to the same propagation path, AFC operations were performed individually in each demodulator.

[Problem to be solved by the invention]

In the conventional automatic frequency control method described above, when the frequency fluctuation of the input modulation signal to the demodulator is large, the sweep width of the VCO must be increased in order to follow the fluctuation and bring it into carrier synchronization. , the disadvantage is that the sweep time increases proportionally.

[Means to solve the problem]

The automatic frequency control system of the present invention mainly operates on a phase detector that inputs and demodulates a phase modulation signal, a carrier regeneration circuit that generates a regenerated carrier signal for phase detection, and a voltage controlled oscillator provided in the carrier regeneration circuit. An automatic frequency control system comprising a plurality of demodulators equipped with an AFC circuit that supplies voltage and performs AFC pull-in by superimposing a sweep voltage in the case of asynchronous operation, and a control device that monitors the plurality of demodulators. wherein the control device receives AFC information from an AFC circuit of at least one synchronized demodulator among the plurality of demodulators and transmits this AFC information to other unsynchronized demodulators; It is characterized by moving the operating center voltage of the voltage controlled oscillator.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. The embodiment of FIG. 1 has modulated signals 21A and 22A.

A plurality of demodulators 21, 22.2 demodulate by inputting 23A.
3N and AFC signals 21 of these demodulators 21 to 23N
B, 22B, 23B, etc. monitoring control and demodulation signal 21
It is composed of a control device 5 that performs sending and receiving of C to C23C to and from the carrier terminal station. The demodulator 21 also includes a phase detector IA that decodes a modulated signal such as PSK modulation, a carrier wave regenerator 2A that regenerates a reference carrier signal for phase detection, and an AFC that performs AFC pull-in when the carrier signal is out of synchronization. circuit 3
A. It is composed of a phase-detected digital signal discriminator 4A. Other demodulators 22 and 23N have similar configurations. Here, the AFC circuit 3A is the VC of the carrier wave regeneration circuit 2A.
An operating voltage is supplied to O, and in the case of asynchronous operation, a sweep voltage is superimposed around this operating voltage to sweep the frequency of the VCO, thereby achieving so-called AFC pull-in.

N types of modulated signals 21 that have now passed through the same signal propagation path
A to 23A tend to have almost the same frequency change, and such modulated signals 21A to 23A are input to the demodulator and demodulated by the reproduced carrier signal. However, if the demodulator 21 is in a synchronized state, It is assumed that the other demodulators 22 and 23N are in an asynchronous state. In such a case, the center voltage of the AFC signal 21B of the demodulator 21A in the synchronized state is transmitted to the control device 5 and stored. Furthermore, the control device 5
transmits the center voltage of this AFC signal 21B to other demodulator AFC circuits 3B, etc. that are in an asynchronous state.
3B, and move the operating point so that it becomes the same voltage as this center voltage.

Since the control operation moves to a state close to AFC pull-in, it is possible to enter the synchronized state with a small AFC sweep width.

〔Effect of the invention〕

As explained above, the present invention inputs an AFC signal from a demodulator in a synchronous state to another demodulator in an asynchronous state and moves its operating voltage, thereby eliminating common frequency fluctuations in the signal propagation path. This makes it possible to eliminate a large amount of the amount. Therefore, the sweep width of the VCO for carrier wave regeneration can be made small, and the synchronization time can be shortened.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention. LA, IB...Phase detector, 2A, 2B...Carrier recovery circuit, 3A, 3B-AF (Jl path, 4A, 4B...
・Discriminator, 5...Control device, 21, 22.23N...
・Demodulator.

Claims (1)

[Claims] A phase detector that inputs and demodulates a phase modulation signal, a carrier regeneration circuit that generates a regenerated carrier signal for phase detection, and a voltage controlled oscillator provided in the carrier regeneration circuit that supplies an operating center voltage to the voltage controlled oscillator. In the automatic frequency control system, the automatic frequency control system includes a plurality of demodulators each having an AFC circuit that performs AFC pull-in by superimposing a sweep voltage on a frequency control system, and a control device that monitors the plurality of demodulators. It receives AFC information from the AFC circuit of at least one demodulator that is synchronized among the demodulators, transmits this AFC information to other demodulators that are not synchronized, and adjusts the operating center voltage of the voltage controlled oscillator. Automatic frequency control method characterized by moving.