JPS58131853A - Interference wave eliminating device - Google Patents

Abstract

PURPOSE:To eliminate an FM interference wave, by providing a filter extracting the interference wave from an input signal and a circuit adjusting the amplitude and phase of the filter output and synthesizing the extracted interference wave with the input signal in the opposite phase and the same level. CONSTITUTION:The FM interference wave having the carrier components being F1, F2 is extracted with a narrow band pass filter from the input signal IFIN. The extracted interference wave is adjusted for the amplitude and phase at an amplitude and phase controlling circuit 6A and applied to a subtractor via a synhesizer 7 together with th input signal. No interference wave exists in the output of the subtractor. This output is given to a control signal generating circuit 9, the remaining interference component is picked up and a control signal for the circuit 6A is formed. Thus, the FM interference wave is eliminated with simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an interference wave removal device, and particularly to an interference wave removal device used in a microwave digital transmission system in which FM interference waves exist from other routes.

In recent years, microwave digital transmission systems have been commercialized and are expected to replace microwave FM transmission systems in the future, but during the transition period, two transmission systems may coexist in the same frequency band. In that case, mutual interference between the two synutems becomes a problem. One example is when a digital transmission system is connected to an FM transmission system using another route.
There may be cases where multiple FM interference occurs. Under such conditions, in order for a digital transmission system to coexist with an FM transmission system, it is necessary to add an FM interference wave removal device to the digital transmission system to configure a system in which the influence of FM interference waves can be ignored.

Therefore, an object of the present invention is to provide a device for removing the above-mentioned FM interference waves.

According to the present invention, in a microwave digital transmission system, either an input signal in which interference waves coexist or an interference wave signal obtained from this input signal through a narrow band filter is controlled by a control signal to control the amplitude and the interference wave signal. control means for controlling the phase; subtraction means for subtracting the output of the control means from the input signal; and orthogonal multiplication means for obtaining the control signal by orthogonally multiplying either one of the signals and the output of the subtraction means. There is obtained an interference wave removal device characterized by comprising the following.

This will be explained in detail below using the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the interference wave removal device according to the present invention.1) It shows the case where there is an FM interference wave having carrier components Fl and F2. First, to explain the configuration itself, ■ and 2 are narrowband filters, 3 and 4 are variable attenuators, 5 and 6 are variable phase shifters, 6A is a combination of 3 to 6 and is an amplitude phase control circuit, and 7 is a synthesizer. , 8 is a subtracter, 9 is a control signal generation circuit, 10 to 1
3 is a multiplier, 14 and 15 are bandpass filters, 16 and 17 are π
/2 phase shifters respectively.

Next, the operation of the apparatus configured as described above will be explained. The FM interference wave having carrier components Fl and F2 contained in the input signal IFXN is extracted by a narrow band filter 1.2, and its output is outputted from an amplitude phase difference formed by a variable attenuator 3.4 and variable phase shifters 5 and 6. The signals are controlled by the control circuit 6A as described later, are combined by the two-combiner 7, and are supplied to the subtracter 8. This subtracter 8 combines the input signal 1F1N and the output of the combiner 7 in a relative relationship such that they are in opposite phase and at the same level. As a result, at the output of the subtracter 8, the interference waves Fl and F2 included in the input signal are eliminated, leaving only the main signal component. The subtracter 8 may be an adder if the above relative conditions are satisfied. The relative relationship in the subtracter 8 described above is maintained by the variable attenuators and variable phase shifters 3 to 6 that are controlled by control signals that will be explained next, but the control signals are obtained by the control signal generation circuit 9. .

FIG. 2 is a vector diagram of the residual interference wave appearing at the output of the subtracter 8, where (a) is related to the phase, (
b) shows things related to amplitude.

If the interference waves included in the input signals F and N are B, and the interference wave of the 7 output is A, then the residual will be 0 in steady state.

As shown in (a), the residual vectors are ΔE1. Δ
When E2, the residual vectors are Δe and Δe2, respectively, as shown in (b).

In the relative relationship in the subtractor 8 as described above.

In the case of a phase shift, a residual interference wave of π/2 or 3π/2 is generated with respect to A, and in the case of an amplitude shift, a residual interference wave of in-phase or anti-phase is generated. Therefore, control signals for the variable attenuators and variable phase shifters 3 to 6 can be obtained by the following operations. That is, the amplitude control signal, which is the control signal for the variable attenuators 3 and 40, is obtained by multiplying the output of the narrow band filter 2 by the residual interference wave passing through π/2 radians (7r/2 phase shifter 16.17). can get.

Further, a phase control signal which is a control signal for the variable phase shifters 5 and 6 is obtained by multiplying the output A of the narrow band filter 2 by the phase interference wave. Bandpass filters 14.15 are used to improve the input to multiplier 10.13 to some extent and stabilize its operation.

As explained above, the control signals for the variable phase shifter 6 and the variable attenuator 4 are obtained from the multiplier 10.11 and the π/2 phase shifter 16, which use the outputs of the subtracter 8 and narrowband filter 2 as input signals. can be obtained by an orthogonal multiplier (9 halves) configured. Similarly, the control signals for the variable attenuator 3 and the variable phase shifter 5 are controlled by quadrature multipliers (other than 9), which are composed of multipliers 12, 13 and bandpass filters 15, which use the outputs of the subtracter 8 and the narrowband filter 1 as input signals. can be obtained by half of

A generally well-known quadrature multiplier is a four-phase phase detector.

In the above operation, each control signal is a signal with an extremely narrow band. Therefore narrowband filter 1
and 2 are not required.

As explained above, according to the embodiment of FIG. 1 according to the present invention, two FM interference waves, Fl and F2, can be canceled. This interference wave cancellation circuit can process all signals in the IF band without using the signals output from the demodulation circuit. As a result, the interference wave removal device according to the present invention can be used alone, and has the advantage that its application is not limited to the type of main signal.

Regarding the type of interference waves, any interference wave in which the carrier component is dominant is possible, and there is no limit to the number of interference waves.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the interference wave removal device according to the present invention, and FIG. 2 is a vector diagram of the residual interference wave that is the output of the subtracter of the device shown in FIG. a
) indicates the phase, and (b) indicates the amplitude. Explanation of symbols: 1 and 2 are narrowband filters, 3 and 4 are variable attenuators, 5 and 6 are variable phase shifters, and 7 is a synthesizer. 8 is a subtracter, 9 is a control signal generation circuit, 10 to 13 are multipliers, 14.15 is a bandpass filter, and 16.17 is a π/2 phase shifter. (7) Horse figure 2 (OL) ACb) Completed

Claims (1)

[Claims] 1. In a microwave digital transmission system, the amplitude and phase of either an input signal in which interference waves coexist or an interference wave signal obtained from this input signal through a narrow band filter are controlled by a control signal. A control means, a subtraction means for subtracting an output of the control means from the input signal, and an orthogonal multiplication means for obtaining the control signal by orthogonally multiplying one of the signals and the output of the subtraction means. An interference wave removal device characterized by: