JP2893145B2 - DC component removal method for envelope frequency analysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of removing a DC component in an envelope frequency analysis for removing a DC component (an average value of a signal) which becomes unnecessary in a system for performing a frequency analysis of an envelope of an amplitude modulated wave. It is.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a functional configuration of a conventional amplitude modulation wave envelope frequency analysis system. As shown in the figure, the conventional envelope frequency analysis system has an input terminal 1, a band selection filtering unit 2 for extracting only a signal component of a band for performing envelope extraction, a square detection unit 3, a low-pass filtering unit 4, a frequency Analysis unit 6, output terminal 7
It consists of.

In general, the frequency analysis of the envelope of an amplitude-modulated wave is simultaneously calculated for signals of a plurality of channels. In other words, a hardware configuration that can simultaneously process a plurality of the flows shown in FIG. 2 in parallel is required. In order to suppress the hardware scale, the amount of memory per channel is determined by the fast Fourier transform in the frequency analysis unit 6 in FIG.
form), the memory required to calculate｝ once,
This is the sum of the memories that store the input signals for the next analysis.

An input terminal 1 receives an amplitude-modulated wave,
The band selection filtering unit 2 performs band selection filtering on the input signal from the input terminal 1 to extract a signal component of a band for performing envelope extraction.
Square detection is performed on the band-selected signal output from the band selection filtering 2, low-pass filtering section 4 performs low-pass filtering processing on the signal after square detection, and frequency analysis section 6 performs frequency analysis. And extract the signal using an appropriate window function
The frequency analysis is performed using T and output to the output terminal 7. Thereafter, the analyzed signal is sent from the output terminal 7 to the display unit and displayed on the waterfall display.

[0005]

However, in the processing method described above, when a large DC component is generated in the square detection unit 3 and the frequency analysis is performed, the DC component is affected by the side lobe of the cutout window function of the signal. There is a drawback that low-frequency peaks not included in the original signal are generated and a correct envelope frequency component cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made to eliminate the above-mentioned problems, to prevent low-frequency peaks not included in the original signal from appearing in the frequency analysis result, and to reduce the amplitude modulation. An object of the present invention is to provide a method for removing a DC component generated in the square detection unit 3 in order to obtain a correct frequency analysis result of a wave envelope.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a method for extracting an envelope from an amplitude modulated wave input signal.
Perform filtering to extract the band component to be performed,
Squared detection of the signal after the filtering, and after the squared detection
Low-pass filtering to the signal of
Obtains the band required for wave number analysis and performs a fast Fourier transform.
How to remove DC component during frequency analysis of wave number analysis system
The squared detected signal, the frequency
The integer multiple of the fast Fourier transform size used in the analysis
A processing block, and the average value of signals in the block and the block
From the average value used one lock before,
Find the average value used for the signal
The DC component is removed by subtracting the average.
It is characterized by the following.

[0008]

According to the present invention, a fast Fourier used in frequency analysis is used.
An integer multiple of the conversion size is regarded as one processing block, and the block
The average value of the signal at the block and the one used before the block
From the average value, calculate the average value used for the signal of the block.
Then, by subtracting the average value from the signal of the block, the DC component generated in the square detection can be removed. Therefore, the leakage of the DC component does not appear in the frequency analysis, and the original correct frequency analysis result can be obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a functional configuration of the envelope frequency analysis system of the present invention. This envelope frequency analysis system includes an input terminal 1, a band selection filtering unit 2, a square detection unit 3, a low-pass filtering unit 4, a DC component removal processing unit 5, a frequency analysis unit 6, and an output terminal 7.

A band selection filtering section 2 filters an input signal from an input terminal 1 to extract a band component from which an envelope is extracted, and a square detection section 3 square-detects the filtered signal to obtain a low-frequency signal. The pass filtering unit 4 performs a low-pass filtering process on the signal after the square detection to obtain a band necessary for performing frequency analysis, and the DC component removal processing unit 5 uses the square detection unit based on the signal after the low band filtering. The DC component generated in the process 3 is removed, the frequency analysis unit 6 cuts out the signal from the signal from which the DC component has been removed using an appropriate window function, performs frequency analysis by FFT, and outputs the frequency analysis result to an output terminal 7. Is output. The output frequency analysis result is displayed on a waterfall display.

[0011] in Figure 1 flow - Cha - with respect to the signal x _m after low-pass filtering 4 in bets, FF of frequency analysis 6
The average value is obtained by the formula (1) in units of an integral multiple of the T size.

(Equation 1) This process is executed by a computer program using a signal of an integral multiple of the FFT size as one unit.

For the first IM input signals, A
Determine the V _1. The AV ₁ the average value of I · M number of signals of Me above start, DC component removal processing unit 5 can be expressed by equation (2), x _m 'is the signal after the DC component removed. x _m ′ = x _m −AV ₁ m = 1 to I · M (2) For the next I · M input signals, AV ₂ is first obtained, and the previous I · M is used without using AV ₂ as it is. Using the average value used for the individual signals, AV ₂ ′ represented by Expression (3) is used as the average value. AV ₂ ′ = p · AV ₂ + q · AV ₁ p + q = 1 (3) That is, a value obtained by integrating the average value calculated for each of the I · M values is used as the average value.

The DC signal component removal processing section 5 for the Nth I · M input signals calculates the following equation (4).

(Equation 2)

The low-pass filtering 4 and the DC component removal processing unit 5 perform a DC component removal process on the signal square-detected by the square detection unit 3 in a random order, and perform a low-pass filtering process on the signal. Also obtains a result equivalent to the above-described processing.

[0015]

As described above, according to the present invention, the following excellent effects can be expected. Since the DC component generated by the squared detection is removed, the leakage of the DC component does not appear at the time of the frequency analysis, and the original correct frequency analysis result can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a functional configuration of an amplitude modulation wave envelope frequency analysis system according to the present invention.

FIG. 2 is a block diagram showing a functional configuration of a conventional amplitude modulation wave envelope frequency analysis system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input signal terminal 2 Band selection filtering part 3 Square detection part 4 Low-pass filtering part 5 DC component removal processing part 6 Frequency analysis part 7 Output terminal

Claims (1)

(57) [Claims] An envelope extraction is performed on an amplitude modulated wave input signal.
Filter to extract the band components
Squared detection of the signal after the filtering,
Apply low-pass filtering to the post-wave signal
To obtain the band required for frequency analysis,
In the DC component removal method at the time of frequency analysis of a system that performs frequency analysis, an integer multiple of the fast Fourier transform size used in the frequency analysis is set as one processing block for the square-detected signal, and the signal in the block is processed. Average value and 1 from the block
Envelope frequency analysis, wherein an average value used for the signal of the block is obtained from the average value used immediately before, and a process of removing a DC component by subtracting the average value from the signal of the block is performed. DC removal method at the time.