CN116506035A - Automatic measurement system for modulation parameters of radio signals - Google Patents

Automatic measurement system for modulation parameters of radio signals Download PDF

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Publication number
CN116506035A
CN116506035A CN202310541605.0A CN202310541605A CN116506035A CN 116506035 A CN116506035 A CN 116506035A CN 202310541605 A CN202310541605 A CN 202310541605A CN 116506035 A CN116506035 A CN 116506035A
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frequency
signal
modulation
wave
amplitude
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黄浩海
姜乃卓
陈佳琦
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Nanjing University
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Nanjing University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/10—Monitoring; Testing of transmitters
    • H04B17/15—Performance testing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/20—Monitoring; Testing of receivers
    • H04B17/29—Performance testing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Abstract

The signal modulation measurement system of the present invention includes: the local oscillation signal source circuit module outputs local oscillation signals; the device comprises an envelope detection circuit module, a stereo frequency modulation demodulation circuit module, a high-speed electronic switch circuit module and a high-speed electronic switch circuit module, wherein the envelope detection circuit module demodulates a single-tone modulated common amplitude modulation wave signal, the stereo frequency modulation demodulation circuit module demodulates a frequency modulation wave signal with a fixed carrier frequency, and the high-speed electronic switch circuit module switches a signal to be detected to be input into an amplitude modulation wave demodulation channel or a frequency modulation wave demodulation channel; switching the demodulated amplitude modulation wave signal or frequency modulation wave signal to enter an output channel; the active mixer circuit module is used for completing the mixing of the input radio signal to be detected and the local oscillation signal; the passive high-pass filter circuit module is used as a frequency-selecting filter and a singlechip after frequency mixing of the frequency modulation signals of the single-tone modulation to be input. The beneficial effects are that: the device can start measurement by one key, and the modulation type identification, demodulation waveform output and measurement display of main modulation parameters of the signal to be measured are all automatically carried out without manual intervention.

Description

Automatic measurement system for modulation parameters of radio signals
Technical Field
The invention belongs to the technical field of analog radio signal demodulation, and particularly relates to an automatic measurement system for modulation parameters of a radio signal.
Background
Analog modulation, such as amplitude modulation and frequency modulation, of high frequency carrier signals is an important way to achieve radio analog communication, which is quite common in practical communication systems. The measurement of modulation parameters of a radio signal enables a rapid and accurate analysis of the basic information of the radio signal, whereas the identification of the modulation type of the radio signal is of great importance in the knowledge of the radio communication system.
But the special measuring device which has the functions of automatic identification of the modulation type of the radio signal, automatic demodulation waveform output of the amplitude modulation and frequency modulation signal, measuring the carrier frequency, amplitude modulation index, frequency modulation index, maximum frequency deviation, demodulation signal frequency and the like of the amplitude modulation and frequency modulation signal is not common in the radio civil scene and the radio experiment teaching at present. The spectrum analyzer can judge and distinguish the amplitude modulation signals and the frequency modulation signals, but the parameters such as the amplitude modulation index of the amplitude modulation wave, the maximum frequency deviation of the frequency modulation wave and the like cannot be directly and quantitatively measured under normal conditions, the hardware cost of the spectrum analyzer is relatively high, the operation is complex, the measurement and the parameter calculation are generally carried out by manually observing the readings, and the automation degree of the measurement process is not high. At present, a plurality of professional modulation domain measuring instruments are designed and used for equipment such as frequency modulation radars and the like, the price is high, the working frequency band is generally at or above GHZ, and the low-cost civil communication and radio experiment teaching requirements are not met.
Disclosure of Invention
The invention provides a signal modulation measuring system for identifying the modulation type of a radio signal and main modulation parameters, which integrates the functions of automatic identification of the modulation signal type of the radio signal, automatic measurement and tracking of carrier frequency, automatic measurement of main modulation parameters and the like, has wide application in the fields of automatic channel searching, detection and positioning of outdoor radio signals, navigation communication of civil ships, radio countermeasure and the like, is also suitable for teaching demonstration and measuring instruments of communication and high-frequency circuit experiments, and aims to achieve the purposes, the technical scheme provided by the invention is as follows:
the modulation parameter automatic measurement system of the radio signal comprises:
the local oscillation signal source circuit module outputs local oscillation signals containing single-frequency sine wave signals and sine wave signals with continuous sweep frequency based on the DDS;
an envelope detection circuit module for demodulating the common amplitude-modulated wave signal modulated by a single frequency,
the stereo modulation-demodulation circuit module is used for demodulating a single-frequency modulated frequency-modulated wave signal with fixed carrier frequency, and the high-speed electronic switch circuit module is used for switching the signal to be detected to be input into an amplitude modulation wave demodulation channel or a frequency modulation wave demodulation channel; switching the demodulated amplitude modulation wave signal or frequency modulation wave signal to enter an output channel; the active mixer circuit module comprises a mixer, wherein the mixer is used for completing the mixing of an input radio signal to be tested and a local oscillation signal, and shifting the frequency spectrum and carrier frequency of the input radio signal to be tested;
The passive high-pass filter circuit module is used as a frequency-selecting filter for inputting the single-frequency modulated frequency-modulated wave signals to be detected after mixing, and the frequency-modulated wave signals after up-conversion are input into the stereo frequency-modulation demodulation module;
the singlechip is used for controlling the DDS to generate a local oscillation signal; the high-speed electronic switch is controlled to carry out ADC sampling and gate an amplitude modulation wave demodulation channel or a frequency modulation wave demodulation channel; the calculation includes: modulation parameters of frequency, spectrum, amplitude modulation index of amplitude modulated signal and frequency modulation index of frequency modulated wave; and judging the modulation type of the signal to be detected, and tracking and measuring the carrier frequency of the single-frequency modulated frequency modulation wave and the carrier frequency of the single-frequency continuous carrier signal which is not modulated.
The automatic measurement system for modulation parameters of radio signals is further designed to further comprise: and the intermediate frequency amplifier circuit module amplifies the input to-be-detected single-frequency modulated common amplitude-modulated wave signal to enable the amplitude of the input to-be-detected amplitude-modulated wave signal to meet the requirement of the input level of the envelope detection module.
The automatic measurement system for modulation parameters of radio signals is further designed to further comprise: the first active low-pass filter circuit is used as a filter of a baseband signal, and the baseband signal is obtained by down-converting an externally input frequency-modulated wave signal to be detected with single frequency modulation through a mixer and a local oscillator signal.
The automatic measurement system for modulation parameters of radio signals is further designed to further comprise: and the second active low-pass filter circuit module is used for carrying out low-frequency filtering on the modulated signals demodulated and output by the envelope detection module and the stereo tone demodulation module, and filtering out high-frequency components and noise.
The automatic measurement system for modulation parameters of radio signals is further designed to further comprise: and the low-frequency amplifier circuit module amplifies the baseband signal after the down-conversion of the mixer and the modulation signal demodulated and output by the stereo modulation circuit module.
The modulation parameter automatic measurement system of the radio signal is further designed in that a superheterodyne structure is adopted to shift and down-convert the frequency spectrum of a signal to be measured to a baseband, and a singlechip is used for sampling the down-converted signal and performing FFT (fast Fourier transform) to obtain the frequency spectrum characteristic of the signal.
The automatic measurement system for the modulation parameters of the radio signal is further designed in that the singlechip judges the modulation type of the signal to be measured and tracks and measures the carrier frequency of the single-frequency modulated frequency modulation wave and the carrier frequency of the single-frequency continuous carrier signal which is not modulated, and the specific process comprises the following steps:
The radio signal to be tested enters an amplitude modulation wave demodulation channel through an electronic switch, the output of an envelope detection circuit is sent to a singlechip for sampling, and if the sampled signal is a standard single-frequency sine wave periodic signal, the input signal is judged to be a common amplitude modulation wave modulated by single frequency;
if the signal is not sinusoidal, inputting the signal to be detected into a frequency modulation wave demodulation channel through an electronic switch again, and judging the type of the frequency modulation wave and measuring the carrier frequency;
in the process of local oscillation signal frequency sweeping, corresponding to each frequency point of the local oscillation signal, the singlechip performs FFT (fast Fourier transform) on the sampling signal to obtain down-converted signalsAccording to the spectrum information of the radio signal to be tested, the signal after down-conversion is sampled by a singlechip, the main characteristics of the spectrum are analyzed by FFT, if the spectrum obtained by the sampling signal through FFT at least comprises two or more frequency spectrum components near zero frequency in the process of sweeping corresponding to a certain frequency of the local oscillator signal, the radio signal to be tested is judged to be a single-frequency modulated frequency modulation wave, according to the spectrum characteristic analysis, when the frequency of the local oscillator signal is the same as the carrier frequency of the frequency modulation wave to be tested, the frequency f of the local oscillator signal corresponding to the moment is recorded 0 ，f 0 Is the carrier frequency of the frequency modulation wave to be measured.
If the frequency spectrum obtained by FFT conversion of the sampling signal does not have at least two frequency components with larger amplitude near zero frequency after the local oscillation signal passes through a complete round of frequency sweep, the signal to be detected is not a frequency modulation wave, and the signal to be detected is an unmodulated single-frequency continuous carrier signal.
The automatic measurement system for the modulation parameters of the radio signal is further designed in that the singlechip calculates the amplitude modulation index m of the common amplitude modulation wave of the single-tone modulation a The specific process is as follows:
1) Amplitude modulation index m of common amplitude modulation wave a Is calculated by (1):
the single frequency modulated AM wave can be described by the mathematical expression:
in the method, in the process of the invention,called amplitude modulation index or amplitude modulation, k a Representing the sensitivity of amplitude modulation, V 0 Representing the amplitude of the unmodulated carrier, V Ω Representing the amplitude of the modulated signal;
can be deduced from the formula (1)
V max And V min Respectively representing the maximum value and the minimum value of the amplitude modulation wave envelope;
the voltage transmission coefficient K of the envelope detection circuit is determined in advance by utilizing the characteristic that the voltage transmission coefficient of the envelope detection circuit is basically unchanged (the voltage transmission coefficient is defined as the amplitude of a demodulation signal/the amplitude of an input amplitude modulation wave envelope) d Sampling and measuring demodulation waveform amplitude U by using single chip microcomputer Ω According to the formula (3), the envelope amplitude m converted into a normal amplitude-modulated wave a Vim, the amplitude modulation index m of the amplitude modulation wave to be measured can be calculated a 。
Wherein K is d U is the voltage transmission coefficient of the detector Ω For the output voltage of the envelope detection circuit, m a For amplitude modulation index, U i Is the amplitude of the carrier voltage.
The automatic measurement system for the modulation parameters of the radio signal is further designed in that the singlechip calculates the frequency modulation index m of the frequency modulation wave to be measured f Maximum frequency offset Δf m The method specifically comprises the following steps:
step 1), measuring a frequency discrimination S curve of the stereo frequency modulation demodulation circuit in advance according to the characteristic that the slope of the frequency discrimination S curve of the stereo frequency modulation demodulation circuit is basically unchanged in a linear region;
step 2) calculating the slope of the frequency discrimination S curve, namely the frequency discrimination sensitivity k of the stereo tone demodulation circuit f The single chip microcomputer samples and measures the voltage amplitude V of the output waveform of the frequency discriminator m Calculating the frequency f of the modulated signal, which is the demodulation waveform, by FFT m According to the frequency discrimination sensitivity k f Calculating the maximum frequency deviation delta f of the corresponding frequency modulation wave to be detected according to the formula (4) m ；
Calculating a frequency modulation index m corresponding to the frequency modulation wave to be measured according to the step (5) f 。
The beneficial effects of the invention are as follows:
1. the measuring device can automatically identify and input the radio signal to be measured, and the identifiable signal modulation type comprises single tone
Normal amplitude modulated wave (AM wave), single tone modulated frequency modulated wave (FM wave), unmodulated single frequency continuous carrier wave.
2. The measuring device can automatically complete demodulation of signals at the same time after automatically identifying the modulation type of the radio signal to be measured
And the function is that the demodulation output waveform has high signal-to-noise ratio and basically no distortion. The main performance index parameters of the measuring device are as follows: the peak-to-peak value range of the input carrier voltage is 50mV-100mV, the carrier frequency range is 10 MHz-30 MHz, and the amplitude modulation wave of single tone modulation is input: amplitude modulation index range 0.2-1.0, modulating signal frequency range 3kHz-5kHz; inputting a tone modulated frequency modulation wave: the frequency modulation index range is 1-6, and the frequency range of the modulated signal is 3kHz-10kHz.
3. The device adopts super heterodyne structure and zero intermediate frequency technology simultaneously, and the output frequency of the local oscillation signal source is stepped to a certain degree and continuous
The frequency sweeping signal and the signal to be detected are mixed, the frequency spectrum of the signal to be detected is moved to a baseband after the output of the mixer is subjected to down-conversion by a low-pass filter, then the baseband signal is sampled by a singlechip and is subjected to FFT calculation, and the frequency spectrum of the baseband signal is analyzed to judge whether the signal to be detected is a frequency modulation wave. By using the method, whether the frequency modulation wave is the frequency modulation wave can be rapidly judged through the sweep frequency of the local oscillation signal, the carrier frequency of the frequency modulation wave is measured, and finally the superheterodyne structure is used for realizing frequency discrimination demodulation output of the frequency modulation wave to be measured.
4. According to the characteristic that the voltage transmission coefficient of the envelope detection circuit is basically unchanged, the voltage transmission coefficient of the envelope detection circuit is measured in advance, the amplitude modulation index of the amplitude modulation wave to be measured can be calculated by only measuring the amplitude of the demodulation waveform through sampling by using a low-cost singlechip and converting the envelope amplitude of Cheng Diaofu waves.
5. According to the characteristic that the slope of the frequency discrimination S curve of the frequency discriminator in a linear region is basically unchanged, the frequency discrimination S curve of the frequency discriminator is measured in advance, the amplitude and the frequency of a demodulation waveform voltage of the frequency discriminator are sampled and measured by using a singlechip, and the maximum frequency deviation of the frequency modulation wave can be calculated, and meanwhile, the corresponding frequency modulation index is calculated.
6. The local oscillator signal source of the device is designed based on the integrated DDS chip, and the advantages of high DDS output frequency precision, continuous and adjustable frequency stepping, high frequency sweep speed, small phase noise of output waveforms, small harmonic distortion and the like are fully utilized. The method can improve the judging speed of the modulation type of the signal to be detected and the measuring precision of the carrier frequency of the frequency modulation wave, thereby further improving the measuring precision of the modulation parameter of the device, improving the signal-to-noise ratio of the demodulation waveform and reducing the distortion degree.
7. In the process of judging the modulation type and measuring the carrier frequency of the frequency-modulated wave, the device uses zero intermediate frequency technology, only needs to sample the baseband signal after mixing the signals to be measured, greatly reduces the requirement on the ADC sampling rate of a processor, can meet the sampling requirement by using the ADC integrated by a singlechip, does not need to use an external high-speed ADC sampling circuit, and greatly reduces the cost of a hardware circuit and the processor.
8. In the measuring process, the FFT is mainly carried out to analyze the frequency spectrum structure and the frequency spectrum component number of the baseband signal, and the requirement on the amplitude precision of the frequency spectrum component is very low, so that the common low-cost singlechip can meet the performance requirement of FFT operation, and the cost of a hardware circuit and a processor is greatly reduced. The device only uses the STM32F4 series singlechip with low cost as a main controller, has high measurement speed and high measurement precision, and the parameter measurement error is basically within 10 percent.
9. The device adopts a full-modularized circuit design, and can realize the expansion and upgrading of the measurement range and the measurement function by adding or replacing an optimized circuit module. For example, a low noise amplifier module and an AGC circuit module are added at the front end of the input channel of the signal to be measured, so that the input dynamic range of the radio signal to be measured can be greatly expanded, and the power range of the input signal in actual measurement can be expanded to-40 dBm to 0dBm.
10. The carrier frequency range of the radio signal to be measured can be expanded by changing the center frequency of the frequency discriminator circuit and the sweep frequency range of the local oscillation signal source, and the carrier frequency range in actual measurement can be expanded to 10MHz to 100MHz. The software control codes, ADC sampling, waveform period and amplitude measurement of demodulation signals, FFT conversion, spectral component analysis and other codes of the singlechip are optimized and upgraded, and the hardware circuit of the device can also be used for judging the type of input digital modulated signals (including ASK, 2FSK and the like) and completing demodulation of digital baseband signals.
Drawings
Fig. 1 is a schematic block diagram of an automatic measurement system for modulation parameters of a radio signal according to the present invention.
Fig. 2 is a schematic circuit diagram of a local oscillator signal source.
Fig. 3 is a circuit diagram of an envelope detection circuit module.
Fig. 4 is a circuit diagram of a stereo fm demodulation module.
Fig. 5 is a circuit diagram of a high-speed electronic switching circuit module.
Fig. 6 is a circuit diagram of a mixer.
Fig. 7 is a circuit diagram of a passive high pass filter.
Fig. 8 is a schematic circuit diagram of an intermediate frequency amplifier.
Fig. 9 is a schematic circuit diagram of a low frequency amplifier.
Fig. 10 is a schematic circuit diagram of a first active low pass filter circuit block (-3 dB cut-off frequency 60 kHz).
Fig. 11 is a circuit diagram of a second active low pass filter circuit block (-3 dB cut-off frequency of 12 kHz).
FIG. 12 shows the amplitude modulation index at maximum (m a =1.0), a waveform chart (lower waveform) and a demodulation waveform chart (upper waveform) of the AM signal to be measured are input.
FIG. 13 shows the minimum amplitude modulation index (m a =0.2), a waveform chart (lower waveform) and a demodulation waveform chart (upper waveform) of the AM wave to be measured are input.
FIG. 14 shows an input single-frequency modulated FM wave with a carrier frequency of 20MHz and maximum modulation frequency and modulation index (modulation signal frequency f=10kHz, modulation index m) f =6) demodulation waveform diagram of the present system.
FIG. 15 shows a frequency modulation wave with an input single frequency modulation, the carrier frequency being 20MHz, the modulation frequency and the modulation index being minimal (modulation signal frequency f=3 kHz, modulation index m) f =1) demodulation waveform diagram of the present system.
Fig. 16 is a flowchart of the operation of the automatic measurement system for modulation parameters of radio signals to determine the modulation type of the signal to be measured.
Fig. 17 shows a theoretical spectrum distribution diagram (the frequency of the modulated signal is 5KHz, and the maximum frequency offset is 10 KHz) after the frequency spectrum of the fm wave to be measured is shifted to the baseband when the frequency of the local oscillation signal is the same as the carrier frequency of the fm wave to be measured.
Fig. 18 is a schematic spectrum diagram obtained by performing FFT conversion on the sampling signal by the singlechip under the condition of fig. 17.
FIG. 19 is a theoretical spectrum distribution diagram (modulation signal frequency 10KHz, maximum frequency offset 60 KHz) when the carrier frequency of the to-be-measured FM wave is shifted to 100KHz when the frequency of the local oscillation signal differs from the carrier frequency of the input to-be-measured single-frequency modulated FM wave by 100 KHz.
Fig. 20 is a schematic spectrum diagram obtained after the single chip microcomputer performs FFT conversion on the sampling signal in the case of fig. 19.
FIG. 21 is a diagram showing a theoretical spectrum distribution (the frequency of the modulated signal is 10KHz, and the maximum frequency offset is 60 KHz) when the difference between the frequency of the local oscillation signal and the carrier frequency of the single-frequency modulated frequency modulation wave input to be measured is greater than or equal to 200 KHz.
Fig. 22 is a schematic spectrum diagram obtained after the single chip microcomputer performs FFT conversion on the sampling signal in the case of fig. 21.
Fig. 23 is a diagram showing a theoretical spectrum distribution diagram when the frequency of the local oscillation signal is the same as the single-frequency continuous carrier frequency to be measured without modulation, and the frequency spectrum of the signal to be measured is shifted to the baseband.
Fig. 24 is a schematic spectrum diagram obtained after the single chip microcomputer performs FFT conversion on the sampling signal in the case of fig. 23.
FIG. 25 is a schematic diagram of a spectrum obtained by FFT transforming a sampling signal by a singlechip when a difference between a frequency of a local oscillation signal and a single-frequency continuous carrier frequency to be measured is greater than or equal to 100KHz, and the carrier frequency of the signal to be measured is shifted to a frequency of 100KHz or higher.
In the real time, when the local oscillator signal source frequency is the same as the carrier frequency of the frequency modulated wave input to be measured and modulated by a single chip microcomputer of the measuring system, the signal is sampled and mixed and then shifted to the baseband, and the actual measurement spectrogram is obtained by FFT (the carrier frequency of the frequency modulated wave is 30MHz, the frequency of the modulated signal is 5kHz, and the maximum frequency offset is 10 kHz).
In the actual measurement, when the local oscillator signal source frequency and the carrier frequency of the input single-frequency modulated frequency modulation wave to be measured are different by 100KHz, the carrier frequency of the single chip microcomputer of the measurement system is shifted to the frequency modulation wave signal of 100KHz after sampling and mixing, and the actual measurement spectrogram is obtained through FFT (the carrier frequency of the frequency modulation wave is 30MHz, the frequency of the modulation signal is 10kHz, and the maximum frequency offset is 60 kHz).
Fig. 28 shows an actual measurement spectrogram obtained by carrying out FFT conversion on a frequency-modulated wave signal with a carrier frequency shifted to 200KHz after sampling and mixing by a single chip microcomputer of the measuring system when the carrier frequency of a local oscillation signal source is different from the carrier frequency of a frequency-modulated wave input to be measured by 200KHz in actual measurement (the carrier frequency of the frequency-modulated wave is 30MHz, the frequency of a modulation signal is 10KHz, and the maximum frequency offset is 60 KHz).
Fig. 29 is a diagram of an actual measurement spectrum obtained by sampling, mixing, and then moving to a baseband signal by a singlechip of the measurement system when the local oscillation signal source frequency is the same as the input single-frequency continuous carrier frequency to be measured, and performing FFT conversion.
(carrier frequency is 30 MHz)
FIG. 30 is a graph of an actual measurement spectrum obtained by sampling and mixing a local oscillation signal source frequency and an input single-frequency continuous carrier frequency to be measured, which is not modulated, by a single chip microcomputer of the measuring system, and then shifting to a 200KHz signal for FFT conversion. (carrier frequency is 30 MHz)
Fig. 31 shows typical actual measurement display results of the automatic measurement system for modulation parameters of radio signals according to the present invention (input signal to be measured is a normal amplitude-modulated wave (AM wave) with carrier frequency of 10MHz, modulation signal frequency of 2kHz, and amplitude modulation index of 1).
Fig. 32 shows typical actual measurement display results of the automatic measurement system of modulation parameters of radio signals according to the present invention (input signal to be measured is a normal amplitude-modulated wave (AM wave) with carrier frequency of 30MHz, modulation signal frequency of 2kHz, and amplitude modulation index of 0.2).
Fig. 33 shows the result of typical practical measurement of the automatic measurement system for modulation parameters of radio signals according to the present invention (the input signal to be measured is a carrier frequency of 10MHz, the frequency of the modulated signal is 10kHz, the frequency modulation index is 6, and the maximum frequency offset corresponds to a frequency modulated wave of 60 kHz).
Fig. 34 shows the result of typical actual measurement of the automatic measurement system for modulation parameters of radio signals according to the present invention (input signal to be measured is carrier frequency 30MHz, modulation signal frequency 3kHz, frequency modulation index 1, corresponding to frequency modulation wave with maximum frequency offset 3 kHz).
Fig. 35 is a schematic diagram showing typical actual measurement display results of the automatic measurement system for modulation parameters of radio signals according to the present invention.
Fig. 36 is a schematic diagram showing typical actual measurement display results of the automatic measurement system for modulation parameters of radio signals according to the present invention.
Detailed Description
The invention will now be described in detail with reference to the accompanying drawings and specific examples.
As shown in fig. 1, the signal modulation measurement system of this embodiment mainly comprises: the system comprises a local oscillator signal source circuit module, an envelope detection circuit module, a stereo tone demodulation circuit module, a high-speed electronic switch circuit module, an active mixer circuit module, a passive high-pass filter circuit module, an intermediate frequency amplifier circuit module, a first active low-pass filter circuit module, a second active low-pass filter circuit module, a low-frequency amplifier circuit module, a singlechip and other modules. The local oscillation signal source circuit module outputs local oscillation signals containing single-frequency sine wave signals and sine wave signals with continuous sweep frequency based on DDS (digital frequency synthesis). And the envelope detection circuit module is used for demodulating the common amplitude-modulated wave signal. The stereo frequency modulation demodulation circuit module is used for demodulating the frequency modulation wave signal with fixed carrier frequency. The high-speed electronic switching circuit module is used for switching the signal to be detected to be input into the amplitude modulation wave demodulation channel or the frequency modulation wave demodulation channel. The demodulated amplitude modulated wave signal or frequency modulated wave signal is switched into the output channel. And switching the demodulation signals of the amplitude modulation wave or the frequency modulation wave signals in the baseband signals or the output channels after the radio signals to be tested are subjected to frequency mixing to carry out ADC sampling. The active mixer circuit module comprises a mixer, a limiting amplifier, a low-noise output amplifier and a bias circuit, wherein the mixer is used for completing the mixing of an input radio signal to be tested and a local oscillator signal and shifting the frequency spectrum and carrier frequency of the input radio signal to be tested. The passive high-pass filter circuit module is used as a frequency-selecting filter for mixing a frequency-modulated signal input to be detected with a single-tone modulation (the modulation signal is a sine wave), and the frequency-modulated signal after up-conversion is input to the stereo frequency-modulation demodulation module. The singlechip is used for controlling the DDS to generate a local oscillation signal; the high-speed electronic switch is controlled to carry out ADC sampling and gate an amplitude modulation wave demodulation channel or a frequency modulation wave demodulation channel; the calculation includes: modulation parameters of frequency, spectrum, amplitude modulation index of amplitude modulated signal and frequency modulation index of frequency modulated wave; judging the modulation type of the signal to be detected; the carrier frequency of the frequency modulated wave of the tone modulation (the modulation signal is a sine wave) is tracked and measured. The signal modulation measurement system of this embodiment further includes an oscilloscope for displaying the modulation parameters.
The types of radio signals to be measured include normal amplitude modulation waves (AM waves) with single frequency modulation (the modulation signal is a sine wave), frequency modulation waves (FM waves) with single frequency modulation (the modulation signal is a sine wave), and unmodulated single frequency continuous carrier signals. The input carrier voltage peak value range is 50mV-100mV, the carrier frequency range is 10 MHz-30 MHz, wherein the carrier frequencies of the frequency modulation wave and the unmodulated single-frequency continuous carrier signal are distributed on the integral multiple frequency of 100KHz, namely the carrier frequency resolution is 100KHz; the carrier frequency resolution of the common amplitude-modulated wave is not limited; the amplitude modulation index range of the amplitude modulated wave is 0.2-1.0, and the frequency range of the modulating signal is 3kHz-5kHz; the frequency modulation index range of the frequency modulation wave is 1-6, and the frequency range of the modulation signal is 3kHz-10kHz.
In this embodiment, the local oscillator signal source circuit module uses the DDS chip AD9910, which can generate a sinusoidal waveform with gradually changed frequency at a clock frequency up to 400MHz, see fig. 2. The module can output single-frequency sine wave signals and sine wave signals with continuous sweep frequency, the frequency of the output signals is continuously adjustable between 1MHz and 100MHz, and the power of the output signals is adjustable between-40 dBm and 0 dBm.
In this embodiment, the envelope detection circuit module uses a detection chip ADL5511 for demodulating a single-tone modulated normal amplitude-modulated wave signal, see fig. 3.ADL5511 has excellent temperature stability, and has an input frequency ranging from dc to 6GHz referenced to the 1.1V internal reference voltage provided by EREF pin. ADL5511 employs a proprietary rectification technique to eliminate the carrier of the input signal to show the true envelope of the modulated signal. Through circuit test, the envelope detection circuit can accurately acquire the envelope of a single-tone modulated common amplitude-modulated wave signal with the bandwidth as high as 1G Hz and the amplitude modulation index within the range of 0.1-1, and the demodulation waveform has no distortion and high signal to noise ratio.
In this embodiment, the stereo FM demodulation circuit module is configured to demodulate a FM signal with a fixed carrier frequency, and the circuit module uses a stereo FM demodulation chip JLAC2090 to modulate an FM phase-locked loop, where the receivable input FM carrier frequency ranges from 87MHz to 108MHz, as shown in fig. 4. The convergence of the power ground and the audio ground at a single point ground near the power supply end in fig. 4 can greatly reduce digital noise. The embodiment uses the singlechip to program and set the carrier center frequency of the chip for receiving the frequency-modulated wave, the frequency of the frequency-modulated wave can not be run when the frequency-modulated wave is demodulated, the frequency-modulated wave has the functions of automatic searching and storing of the frequency-modulated wave, and the volume and the frequency of the frequency-modulated wave can be automatically memorized when the power is off. For the set FM stereo input channel, the frequency modulation demodulation module has stronger frequency stability, and the interference of other external radio signals is greatly reduced. The carrier center frequency of the received frequency modulated wave is programmed to be 100MHz in the device. Through testing, the stereo frequency modulation demodulation circuit has excellent performance index, the center frequency basically has no drift after long-time work, the linearity of the frequency discrimination curve of the frequency discriminator circuit is good, the output demodulation waveform is stable, the signal to noise is high, and almost no distortion exists. The stereo tone demodulation circuit module can use binaural demodulation and has the advantages of high integration level, low power consumption, high sensitivity, high output signal to noise ratio, simple use and the like.
In this embodiment, the high-speed electronic switch circuit module uses the high-speed electronic switch chip CH440G, see fig. 5, to support a switching rate higher than 1kHz, and the frequency range of the input signal channel includes a frequency band from 10MHz to 30MHz, and the high-speed electronic switch implements the function of switching the input signal to be tested into the amplitude modulation wave demodulation channel and the frequency modulation wave demodulation channel.
In this embodiment, the active mixer circuit module uses an analog multiplier AD831 chip, see fig. 6. The AD831 is an integrated mixer chip, and includes a mixer, a limiting amplifier, a low noise output amplifier, a bias circuit, and the like inside. When the AD831 forms a mixer circuit, the bandwidth of the input signal and the local oscillation signal can reach 500MHz at the highest, and the intermediate frequency output modes are respectively differential current output (the output frequency can reach 250MHz at the highest) and single-ended voltage output. (the output frequency can be up to 200 MHz). The mixer circuit formed by the AD831 has good linearity, the output impedance realizes 50Ω matching, the circuit has no insertion loss, the combined frequency and the leakage of the local oscillation and the input signal after mixing are smaller by reasonably controlling the power of the local oscillation signal and the input signal, no stray component is basically generated, and the mixer circuit has better performance. The mixer circuit module is used for realizing the function of mixing the input radio signal to be tested with the local oscillation signal and shifting the frequency spectrum and the carrier frequency of the input radio signal to be tested.
In this embodiment, the passive high pass filter circuit module uses LC elements to construct a nine-order butterworth passive filter with a-3 dB cut-off frequency of 30MHz, see fig. 7. The passive high-pass filter circuit module is used as a frequency-selecting filter after frequency-modulating signals (modulating signals are sine waves) to be detected are mixed (up-converted), down-converted signals after frequency-modulating signals (frequency-modulating signals) to be detected and local oscillation signals are input are filtered, the up-converted frequency-modulated signals are selected to be input into the stereo frequency-modulating demodulation module, and the carrier center frequency of the frequency-modulated signals is shifted to 100MHz.
In this embodiment, the intermediate frequency amplifier circuit module uses a high-speed operational amplifier chip (OPA 847), the operating frequency range includes the frequency range from 10MHz to 100MHz, the gain is 23dB and above, and the circuit schematic diagram of the module is shown in fig. 8. The intermediate frequency amplifier amplifies the common amplitude-modulated wave signal input to the single frequency modulation to be detected (the modulation signal is sine wave), and improves the signal to noise ratio, so that the amplitude of the amplitude-modulated wave signal input to the to-be-detected reaches the requirement of the input level of the envelope detection module.
In this embodiment, the low frequency amplifier circuit module uses an operational amplifier chip (OPA 227), the operating frequency range includes the frequency range from 100Hz to 1MHz, the gain is 14dB and above, and the circuit schematic diagram of the module is shown in fig. 9. The low-frequency amplifier amplifies the baseband signal (-3 dB cutoff frequency is the output signal of the low-pass filter with 60 KHz) after the down-conversion of the mixer and the modulated signal demodulated and output by the stereo FM demodulation circuit module.
In the embodiment, the active low-pass filter 1 circuit module uses a precision operational amplifier chip OPA227 to form a Butterworth fourth-order MFB filter, the-3 dB cutoff frequency is 60kHz, and the frequency response in the passband is gentle. The schematic circuit diagram of the module is shown in fig. 10. The active low-pass filter 1 is used as a baseband filter, and selects a baseband signal obtained by a mixer (down-conversion) of a frequency-modulated wave signal input to be detected with single frequency modulation (the modulation signal is a sine wave).
In the embodiment, the active low-pass filter 2 circuit module uses a precision operational amplifier chip OPA227 to form a Butterworth fourth-order MFB filter, the-3 dB cutoff frequency is 12kHz, and the frequency response in the passband is gentle. The schematic circuit diagram of the module is shown in fig. 11. The active low-pass filter 2 carries out low-pass filtering on the modulated signals demodulated and output by the envelope detection module and the stereo tone demodulation module, filters out high-frequency components and noise, reduces waveform distortion and improves signal to noise ratio.
The input impedance and the output impedance of each circuit module are 50 ohms, and the modules are connected by coaxial lines; the grounding of each module adopts a resistor of 0 ohm to be grounded at one point.
In the present embodiment, the input channel of the stereo tone demodulation circuit block is set to 100MHz. When judging that the input radio signal to be measured is a Frequency Modulation (FM) wave with single frequency modulation (the modulation signal is sine wave), determining the carrier frequency f of the input FM signal to be measured by continuous sweep of the local oscillator signal source 0 Then the singlechip controls the output frequency of the local oscillation signal source to be equal to 100MHz-f 0 Is provided. For example, if the carrier frequency of the FM signal to be measured is 10MHz, the output frequency of the local oscillation signal source is set to 90MHz; if the carrier frequency of the FM signal to be measured is 20MHz, the output frequency of the local oscillation signal source is set to 80MHz. After the local oscillation signal and the input FM signal to be detected are multiplied by the mixer, the FM signal after up-conversion is taken out by the passive LC high-pass filter, at the moment, the carrier frequency of the input FM signal to be detected is changed into 100MHz, the input FM signal is aligned with the 100MHz of the input fixed channel of the stereo FM demodulation module, the performance of the stereo FM demodulation module can be fully exerted, the final demodulation waveform output is obtained after the demodulation output signal is amplified at low frequency and filtered at low pass, the signal-to-noise ratio of demodulation waveform is greatly improved, and the working stability of a measuring device and the measuring precision of FM signal parameters are improved.
In this embodiment, the measuring device has three electronic switches, which are all controlled by a single-chip microcomputer. The first electronic switch controls the input channel of the radio signal to be detected, and can switch the input of the signal to be detected into an amplitude modulation wave demodulation channel or a frequency modulation wave demodulation channel; the second electronic switch controls the demodulation output port of the measuring device, and can switch the demodulation output of the amplitude modulation wave or the demodulation output of the frequency modulation wave; and the third electronic switch controls an ADC sampling signal channel of a singlechip of the measuring device, and can switch an output demodulation signal of the sampling measuring device or a baseband signal after mixing (down-conversion) of a radio signal to be measured.
In this embodiment, the mixer performs multiplication of the input radio signal to be measured and the local oscillation signal, and shifts the frequency spectrum of the input radio signal to be measured to a desired position. When judging the frequency modulation type, the frequency spectrum of the input frequency modulation signal is moved to the baseband through frequency mixing (down conversion), the singlechip samples the baseband signal and carries out FFT frequency spectrum analysis, and whether the frequency modulation signal is frequency modulation is judged according to the components of the frequency spectrum components. When the frequency modulation wave demodulation is carried out, the frequency spectrum of an input frequency modulation signal is subjected to frequency mixing up-conversion, the carrier frequency of the frequency modulation signal is moved to the position of 100MHz of an input fixed channel of a stereo frequency modulation demodulation module, the performance of the stereo frequency modulation demodulation module is fully utilized, a final demodulation waveform output is obtained after the demodulation output signal is subjected to low-frequency amplification and low-pass filtering, the signal-to-noise ratio of the demodulation waveform is greatly improved, and the working stability of a measuring device and the measuring precision of frequency modulation signal parameters are improved.
In this embodiment, the radio signal to be measured may be divided into two paths after being selected by the first high-speed electronic switch, one path is input into the amplitude modulation wave demodulation circuit channel, and the other path is multiplied by the local oscillation signal through the mixer and then input into the frequency modulation wave demodulation circuit channel.
In the channel of the amplitude modulation wave demodulation circuit, a signal to be detected firstly passes through a broadband intermediate frequency amplifier with a gain of 26dB, amplifies an amplitude modulation wave signal to enable the amplitude to meet the requirement of the input level of a detector, then demodulates an original modulation signal through an envelope detection circuit, finally filters out high-frequency components, spurious signals and high-frequency noise contained in the demodulation signal through a low-pass filter with a cut-off frequency of 12kHz, and finally obtains the final single-tone modulated amplitude modulation wave demodulation waveform output.
In this embodiment, the demodulation and modulation parameter measurement ranges of the device for the amplitude-modulated wave are: the input is amplitude-modulated wave of single frequency modulation (the modulating signal is sine wave), the carrier wave frequency range is 10MHz-30MHz, the modulating signal frequency range is 3kHz-5kHz, and the amplitude modulation index range is 0.2-1.0. The input signal to be measured is amplitude-modulated wave with carrier frequency of 20MHz, modulated signal frequency of 2kHz and amplitude modulation index of 1.0 (corresponding to the measurable maximum amplitude modulation index), and the time domain waveform (upper waveform) and amplitude-modulated wave input waveform (lower waveform) of the demodulated signal are shown in figure 12; the input signal to be measured is an amplitude modulation wave (corresponding to the measurable minimum amplitude modulation index) with the carrier signal of 20MHz, the modulation signal frequency of 2kHz and the amplitude modulation index of 0.2, and the time domain waveform (upper waveform) and the amplitude modulation wave input waveform (lower waveform) of the demodulation signal are shown in figure 13.
In determining carrier frequency f of FM signal 0 Setting the frequency of local oscillation signal as 100MHz-f 0 And (3) moving the carrier frequency of the frequency-modulated signal to be detected to a fixed 100MHz (corresponding to a fixed 100MHz input channel of the stereo frequency-modulated demodulation module) through up-conversion of the mixer, then realizing frequency discrimination by using the stereo frequency-modulated demodulation module, and obtaining final demodulation waveform output after low-frequency amplification and low-pass filtering of a demodulation output signal.
In this embodiment, the demodulation and modulation parameter measurement range of the system for the frequency modulation wave is: the frequency modulation wave is input as single-frequency modulation (the modulation signal is sine wave), the carrier wave frequency range is 10MHz-30MHz, the carrier wave frequency of the frequency modulation wave and the unmodulated single-frequency continuous carrier wave signal is distributed on the integral multiple frequency of 100KHz, namely the frequency resolution of the carrier wave is 100KHz; the frequency range of the modulated signal is 3kHz-10kHz, and the frequency modulation index range is 1-6. The carrier frequency of the input frequency-modulated wave to be detected is 20MHz, the frequency of the modulated signal is 10kHz, the frequency modulation index is 6 frequency-modulated wave (corresponding to the measurable maximum modulation frequency and maximum frequency deviation), and the time domain waveform of the demodulated signal is shown in figure 14; the carrier frequency of the input frequency-modulated wave to be measured is 20MHz, the frequency of the modulated signal is 3kHz, the frequency modulation index is 1 (corresponding to the measurable minimum modulation frequency and minimum frequency deviation), and the time domain waveform of the demodulated signal is shown in figure 15.
The specific process of judging the modulation type of the signal to be detected by the singlechip is as follows: the radio signal to be tested firstly enters an AM demodulation circuit through an electronic switch, the output of an envelope detection circuit is sent to a singlechip for sampling, and if a standard single-frequency sine wave periodic signal is sampled, the input signal can be judged to be a common amplitude modulation wave with single-frequency modulation (the modulation signal is a sine wave);
if the signal is not sinusoidal, the signal to be detected is input into the FM demodulation circuit module through the electronic switch again, and the frequency modulation wave type judgment and the carrier frequency tracking measurement are carried out.
In the frequency modulation wave type judging and demodulating circuit, a superheterodyne structure is adopted, a local oscillation signal source outputs a sweep frequency signal with the frequency of 100KHz in a stepping way, the sweep frequency range is 10MHz-30MHz (the carrier frequency range of an input radio signal to be detected is covered), the local oscillation signal and the input signal to be detected are mixed through an active mixer, the output signal of the mixer is subjected to frequency spectrum down-conversion to a baseband through a first active low-pass filter circuit with the cut-off frequency of 60kHz, then voltage amplification is carried out through a low-frequency amplifier circuit, and finally the frequency spectrum is switched through a high-speed electronic switching circuit and then is input into a singlechip for sampling. In the process of local oscillation signal frequency sweeping, corresponding to each frequency point of the local oscillation signal, the singlechip performs FFT conversion on the sampling signal, so that spectrum information of the radio signal to be detected after down-conversion can be obtained. And (3) according to the signals subjected to down-conversion by using the singlechip, carrying out FFT (fast Fourier transform) to analyze the main characteristics of the frequency spectrum, and judging the modulation type of the signals to be detected.
If the frequency spectrum obtained by FFT conversion of the sampling signal contains at least two or more frequency spectrum components with larger amplitude near zero frequency during the frequency sweep process corresponding to a certain frequency of the local oscillation signal, as shown in fig. 18, it can be judged that the radio signal to be measured is a single-frequency modulated (modulated signal is a sine wave) frequency modulation wave (FM wave), and the frequency of the local oscillation signal is the same as the carrier frequency of the frequency modulation wave to be measured at this time, and the corresponding local oscillation signal frequency f is recorded according to the spectral feature analysis and fig. 18 0 ，f 0 Is the carrier frequency of the frequency modulation wave to be measured. The singlechip samples the down-converted signal to complete FFT conversion and spectral feature analysis, and the principle of judging the modulation type is already explained and is not repeated here.
If the frequency spectrum obtained by FFT conversion of the sampling signal does not have at least 2 frequency components with larger amplitude near the zero frequency (only one frequency component with larger amplitude near the zero frequency) after the local oscillation signal passes through a complete round of frequency sweep, the signal to be detected is not a frequency modulation wave, and the signal to be detected is an unmodulated single-frequency continuous carrier signal.
In the sweep process of the local oscillation signal, when a frequency component with larger amplitude appears at a position close to zero frequency in a frequency spectrum obtained by FFT conversion of a sampling signal, the frequency f of the local oscillation signal at the moment is recorded 0 As can be seen from the above-mentioned spectral signature analysis and fig. 24, the frequency and unmodulated local oscillator signal are nowSingle frequency continuous carrier frequency is the same, f 0 Is the single-frequency continuous carrier frequency to be measured without modulation.
After judging and knowing the modulation type of the signal to be measured, the system uses a singlechip to measure the amplitude modulation index m of the amplitude modulation wave of single-frequency modulation (the modulation signal is sine wave) a The specific process is as follows:
1) Amplitude modulation index m of common amplitude modulation wave a Is calculated by (1):
the single frequency modulated AM wave can be described by the mathematical expression:
in the method, in the process of the invention,called amplitude modulation index or amplitude modulation, k a Representing the sensitivity of amplitude modulation, V 0 Representing the amplitude of the unmodulated carrier, V Ω Representing the amplitude of the modulated signal;
can be deduced from the formula (1)
V max And V min Respectively representing the maximum value and the minimum value of the amplitude modulation wave envelope;
the voltage transmission coefficient K of the envelope detection circuit is determined in advance by utilizing the characteristic that the voltage transmission coefficient of the envelope detection circuit is basically unchanged (the voltage transmission coefficient is defined as the amplitude of a demodulation signal/the amplitude of an input amplitude modulation wave envelope) d Sampling and measuring demodulation waveform amplitude U by using single chip microcomputer Ω According to the formula (3), the envelope amplitude m converted into a normal amplitude-modulated wave a Vim, the amplitude modulation index m of the amplitude modulation wave to be measured can be calculated a 。
Wherein K is d U is the voltage transmission coefficient of the detector Ω For the output voltage of the envelope detection circuit, m a For amplitude modulation index, U i Is the amplitude of the carrier voltage.
After judging and knowing the modulation type of the signal to be measured, the system uses the singlechip to measure the maximum frequency spectrum delta f of the frequency modulation wave of single-frequency modulation (the modulation signal is sine wave) m And frequency modulation index m f The specific process is as follows:
in tracking and measuring carrier frequency f of frequency modulated wave (FM wave) of single frequency modulation (modulating signal is sine wave) 0 Setting the frequency of the local oscillation signal source to be 100MHz-f 0 And (3) moving the carrier frequency of the frequency-modulated signal to be detected to a fixed 100MHz (corresponding to a fixed 100MHz FM wave input channel of the stereo frequency-modulated demodulation circuit module) through up-conversion of the mixer, then demodulating the frequency-modulated wave, namely frequency discrimination, by using the stereo frequency-modulated demodulation circuit module, and obtaining a final demodulation waveform output after the demodulation output signal passes through a second active low-pass filter and a low-frequency amplifier.
Step 1), measuring a frequency discrimination S curve of the stereo frequency modulation demodulation circuit in advance according to the characteristic that the slope of the frequency discrimination S curve of the stereo frequency modulation demodulation circuit is basically unchanged in a linear region;
step 2) calculating the slope of the frequency discrimination S curve, namely the frequency discrimination sensitivity k of the stereo tone demodulation circuit f The single chip microcomputer samples and measures the voltage amplitude V of the output waveform of the frequency discriminator m Calculating the frequency f of the modulated signal, which is the demodulation waveform, by FFT m According to the frequency discrimination sensitivity k f Calculating the maximum frequency deviation delta f of the corresponding frequency modulation wave to be detected according to the formula (14) m ；
Calculating a frequency modulation index m corresponding to the frequency modulation wave to be measured according to the step (15) f 。
The output of the envelope detection circuit is subjected to a low-pass filter to obtain a demodulation waveform of the amplitude-modulated wave; the single chip microcomputer ADC samples the demodulation waveform, calculates and measures and simultaneously displays the modulation type of the signal to be measured on the liquid crystal screen, and demodulates the main modulation parameters such as the waveform, frequency spectrum, amplitude modulation index of the amplitude modulation signal and the like of the signal.
When the signal to be detected is judged to be a frequency modulation wave (FM wave) of single-frequency modulation (the modulation signal is a sine wave), the high-speed electronic switch circuit module switches the channel of the frequency modulation wave demodulation circuit to which the signal to be detected is input, and the output of the frequency discriminator circuit is subjected to low-pass filtering and amplification to obtain a demodulation waveform of the frequency modulation wave; the single chip microcomputer ADC samples the demodulation waveform, calculates and measures and simultaneously displays the modulation type of the signal to be measured, and main modulation parameters such as waveform, frequency spectrum, frequency modulation index of the demodulation signal and the like of the frequency modulation signal on the liquid crystal screen.
When the signal to be measured is judged to be an unmodulated single-frequency continuous carrier signal, the singlechip measures the frequency of the carrier signal and simultaneously displays the modulation type and the carrier frequency of the signal to be measured on the liquid crystal screen.
As shown in fig. 16, a software code algorithm for discriminating whether or not the modulation type is an amplitude-modulated wave of single frequency modulation (the modulation signal is a sine wave) is briefly described: the singlechip ADC acquires the final output signal of the AM demodulation circuit, and the peak-to-peak value of the demodulation signal is measured and calculated. In order to reduce measurement errors caused by jitter of demodulation waveforms during ADC acquisition, a fourth maximum value and a fourth minimum value of demodulation signal waveforms in a certain sampling time are measured respectively, the peak values of the demodulation waveforms are obtained by subtracting the fourth maximum value and the fourth minimum value, and an average value is obtained after multiple measurements. And setting a proper voltage threshold, comparing the average value of the demodulated signal measurement with the threshold, and judging that the demodulated waveform is a sine wave if the average value is larger than the threshold, and judging that the modulation type of the input signal to be detected is a single-tone modulated amplitude modulation wave. The above is circularly executed every a short period of time in the program code, if the average value of the demodulated signal measurement is smaller than the threshold value, the cycle is jumped out, and meanwhile, the input signal to be detected is judged not to be the amplitude modulation wave of the single tone modulation.
Software code algorithm profile for determining whether the modulation type is a single frequency modulated (the modulated signal is a sine wave) frequency modulated wave or an unmodulated single frequency continuous carrier signal: the singlechip controls the local oscillation signal source to output continuous sweep frequency signals, the sweep frequency range is set to be 10MHz-30MHz (the carrier frequency range covering the input radio signal to be tested), and the sweep frequency step length is set to be 100kHz.
And in each frequency point in the local oscillation signal frequency sweeping process, the singlechip samples the baseband signal which is output by the mixer through the first active low-pass filter circuit with the cutoff frequency of 60KHz in a down-conversion mode, performs FFT conversion on the sampled signal, and analyzes the frequency spectrum of the baseband signal. If the frequency spectrum obtained by FFT conversion of the sampling signal contains at least two or more frequency spectrum components with larger amplitude near zero frequency in the local oscillation frequency sweeping process corresponding to a certain frequency of the local oscillation signal, as shown in fig. 18, it can be judged that the radio signal to be detected is a single-frequency modulated (modulated signal is a sine wave) frequency modulation wave (FM wave), and the frequency of the local oscillation signal is the same as the carrier frequency of the frequency modulation wave to be detected at this time according to the spectral feature analysis and fig. 18, and the corresponding local oscillation signal frequency f is recorded 0 ，f 0 Is the carrier frequency of the frequency modulation wave to be measured. The cycle is then exited and the sweep process is temporarily suspended. If the frequency spectrum obtained by FFT conversion of the sampling signal does not have at least 2 frequency components with larger amplitude near the zero frequency (only one frequency component with larger amplitude near the zero frequency) after the local oscillation signal passes through a complete round of continuous sweep frequency circulation, the signal to be detected is not a frequency modulation wave, and the signal to be detected is an unmodulated single-frequency continuous carrier signal. In the sweep process of the local oscillation signal, when a frequency component with larger amplitude appears at a position close to zero frequency in a frequency spectrum obtained by FFT conversion of a sampling signal, the frequency f of the local oscillation signal at the moment is recorded 0 As can be seen from the above-mentioned spectral feature analysis and fig. 24, the frequency of the local oscillation signal is the same as the unmodulated single-frequency continuous carrier frequency, f 0 And ending the circulation for the single-frequency continuous carrier frequency to be detected without modulation, and temporarily suspending the frequency sweeping process.
Taking the FM wave test of single-tone modulation with carrier frequency of 10MHz, modulation signal frequency of 5kHz and maximum frequency deviation of 20KHz as an example, the test results in the frequency sweeping process are shown in figures 26, 27 and 28. When the output frequency of the local oscillation signal source is the same as the FM wave carrier frequency to be measured in the frequency sweeping process, as shown in figure 26, the spectral lines with larger amplitude and clarity are obviously visible on the baseband signal spectrogram measured by the singlechip at the positions of 5kHz, 10kHz and the like; when the difference between the output frequency and the FM wave carrier frequency to be measured in the sweep process of the local oscillation signal source is equal to 100KHz, as shown in figure 27, the single chip microcomputer measures high-order sideband components with smaller residual amplitude near 2KHz and 12KHz on the baseband signal spectrogram; when the phase difference between the output frequency of the local oscillation signal source and the carrier frequency of the FM wave to be measured is greater than or equal to 200KHz in the frequency sweeping process, as shown in figure 28, no obvious spectral line component with larger amplitude and definition can be seen on the baseband signal spectrogram measured by the singlechip.
Taking an example of the test of an unmodulated single-frequency continuous carrier signal with a carrier frequency of 10MHz, the test results during the frequency sweep are shown in fig. 29 and 30. When the output frequency of the local oscillation signal source is the same as the single-frequency continuous carrier frequency to be measured in the frequency sweeping process, as shown in fig. 29, the spectrum of the down-conversion signal measured by the singlechip is obviously visible to have a clear spectral line with larger amplitude near the low-frequency position; when the output frequency of the local oscillation signal source is different from the single-frequency continuous carrier frequency to be measured (the phase difference is 100KHz or more), as shown in fig. 30, the spectrum of the down-conversion signal measured by the singlechip cannot be seen to have obvious spectral line components with larger and clear amplitude near the low-frequency position.
The actual measurement process verifies that the frequency spectrum of the signal to be measured is shifted to the baseband by adopting the superheterodyne structure, the signal after the frequency spectrum is sampled by the singlechip, the FFT is completed to obtain the frequency spectrum characteristics of the signal, the judgment of the frequency modulation wave type and the carrier frequency tracking measurement method are carried out, the judgment of the frequency modulation wave type of single-frequency modulation (the modulation signal is a sine wave) can be accurately realized, and meanwhile, the carrier frequency of the frequency modulation wave is accurately and rapidly measured.
The specific process of obtaining the frequency spectrum characteristics of the signal by FFT transformation is as follows: firstly, a local oscillation signal source outputs a sweep frequency signal with the frequency of 100KHz, the sweep frequency range is 10MHz-30MHz (the carrier frequency range of an input radio signal to be tested is covered), the local oscillation signal and the input signal to be tested are mixed through an active mixer, and the output signal of the mixer is subjected to frequency down-conversion and shifted to a baseband through a first active low-pass filter circuit with the cut-off frequency of 60 KHz. The down-converted radio signal to be tested is subjected to voltage amplification through a low-frequency amplifier circuit, and finally is switched through a high-speed electronic switch circuit and then is input into a singlechip for sampling. In the process of local oscillation signal frequency sweeping, corresponding to each frequency point of the local oscillation signal, the singlechip performs FFT conversion on the sampling signal, so that spectrum information of the radio signal to be detected after down-conversion can be obtained.
If the input signal to be measured is a single-frequency modulation wave, according to the requirement that the carrier frequency resolution of the frequency modulation wave is 100KHz (namely, the carrier frequency of the frequency modulation wave is an integer multiple of 100 KHz), the sweep frequency step length of the local oscillation signal is 100KHz, and the following 3 situations exist in the spectrum information obtained after the singlechip performs FFT conversion on the sampling signal in the sweep frequency process.
1) When the frequency of the local oscillation signal is the same as the carrier frequency of the frequency modulation wave to be detected, the frequency spectrum of the frequency modulation wave to be detected is shifted to the baseband, and the distribution of sideband components in the frequency spectrum is shown as shown in figure 17 according to theory (the frequency of the modulation signal is 5KHz, and the maximum frequency offset is 10 KHz).
The actual spectrum distribution obtained by the singlechip after carrying out FFT conversion on the sampling signal is shown in figure 18. The sampling frequency fs of the singlechip is 62KHz, and the distribution of sideband components with larger amplitude in the frequency spectrum distribution diagram is symmetric about fs/2, namely 31 KHz.
2) When the difference between the frequency of the local oscillation signal and the carrier frequency of the frequency modulation wave is equal to 100KHz, the carrier frequency of the frequency modulation wave to be measured is moved to
At the frequency of 100KHz, most of the frequency spectrum components are located outside the channel of the low-pass filter and filtered by the low-pass filter, and only a small amount of high-order sideband components with smaller amplitude are remained in the channel of the low-pass filter, so that the distribution of the sideband components in the frequency spectrum is shown as shown in figure 19 according to theory (the frequency of a modulation signal is 10KHz, and the maximum frequency offset is 60 KHz).
The actual spectrum distribution diagram obtained by the singlechip after carrying out FFT conversion on the sampling signal is shown in figure 20. The sampling frequency fs of the singlechip is 62KHz, and the high-order sideband components with smaller residual amplitude in the frequency spectrum distribution diagram are symmetrically distributed about fs/2, namely 31 KHz.
3) When the difference between the frequency of the local oscillation signal and the carrier frequency of the frequency modulation wave is greater than or equal to 200KHz, the carrier frequency of the frequency modulation wave to be measured
Moving to 200KHz and higher, the spectral components are all outside the channel of the low-pass filter, and are filtered by the low-pass filter, and the spectrum does not contain any component, as shown in fig. 21 (the frequency of the modulated signal is 10KHz, and the maximum frequency offset is 60 KHz).
The actual spectrum distribution obtained by the singlechip after carrying out FFT conversion on the sampling signal is shown in figure 22. The sampling frequency fs of the singlechip is 62KHz, and the spectrum after FFT conversion does not contain any component.
If the input signal to be measured is an unmodulated single-frequency continuous carrier signal, according to the requirement of the measuring system on the carrier frequency resolution of 100KHz (namely, the unmodulated single-frequency continuous carrier signal is located at the integral multiple of 100 KHz), the sweep frequency step length of the local oscillation signal is 100KHz, and the following 2 cases exist in the spectrum information obtained after the singlechip performs FFT conversion on the sampling signal in the sweep frequency process.
1) When the frequency of the local oscillation signal is the same as the single-frequency continuous carrier frequency to be measured, the frequency spectrum of the signal to be measured is shifted to the base
The frequency of the band is not completely identical when the system actually measures, because the local oscillation signal and the unmodulated single-frequency continuous carrier signal come from different frequency sources and belong to incoherent signals. Assuming that the frequency difference between the two is deltaf (less than 1 KHz), after passing through the low-pass filter, the spectrum only contains spectral components with the frequency deltaf, as shown in fig. 23.
The actual spectrogram obtained by the singlechip after carrying out FFT on the sampling signal has a low-frequency component deltaf, as shown in fig. 24.
2) When the difference between the frequency of the local oscillation signal and the single-frequency continuous carrier frequency to be measured is greater than or equal to 100KHz, the carrier frequency of the signal to be measured is moved to the frequency of 100KHz and higher, the frequency spectrum components of the signal to be measured are all positioned outside the channel of the low-pass filter and filtered by the low-pass filter, and the frequency spectrum does not contain any component.
The actual spectrum distribution obtained by the singlechip after carrying out FFT conversion on the sampling signal is shown in figure 25. The sampling frequency fs of the singlechip is 62KHz, and the spectrum after FFT conversion does not contain any component, as shown in figure 25.
In this embodiment, the signal modulation measurement system uses an STM32F407 single-chip microcomputer as a main controller and a computing core unit of the device system, and the key input and the liquid crystal display are respectively used as a man-machine interface input device and an output display device of the measurement system. The measuring system is simple and convenient to operate, does not need manual control intervention, can automatically identify the modulation type (including the amplitude modulation wave of single-frequency modulation (the modulation signal is sine wave), the frequency modulation wave of single-frequency modulation (the modulation signal is sine wave) and the continuous single-frequency carrier signal which is not modulated) of the input signal to be measured by one-key starting, and displays the judging result of the modulation type, the amplitude modulation index of the amplitude modulation wave, the carrier frequency of the frequency modulation wave, the corresponding frequency modulation index, the maximum frequency deviation, the demodulation signal waveform diagram, the modulation signal frequency, the modulation signal spectrogram and other information on the liquid crystal screen in real time, and simultaneously automatically outputs the demodulation waveforms of the amplitude modulation wave and the frequency modulation wave.
In this embodiment, a plurality of test points are reserved in the measurement system, so that the local oscillation signal waveform can be observed, the mixer outputs the waveform, the frequency response of each filter is tested, and the demodulation output waveforms of the amplitude modulation wave and the frequency modulation wave can be accessed to the oscilloscope for observation.
In the present embodiment, typical actual measurement display results of the signal modulation measurement system of the present invention are shown in fig. 31 to 36.
The input signal to be tested corresponding to fig. 31 is a normal amplitude modulation wave with carrier frequency of 10MHz, modulation signal frequency of 2kHz and single frequency modulation (modulation signal is sine wave) with amplitude modulation index of 1. The liquid crystal screen of the measuring system displays an automatic measuring result, the modulation type is judged to be a single-tone modulated amplitude modulation wave, the frequency of a modulation signal is 2.016kHz, the amplitude modulation index is 1.0, and meanwhile, information such as a waveform chart, a modulation signal spectrogram and the like which are output by demodulation of the amplitude modulation wave is displayed. From the measurement data displayed on the screen, the modulation type is judged correctly, the frequency of the measured demodulation signal is 2.016kHz, and the relative error of frequency measurement is 0.8%; the amplitude modulation index was measured to be 1.0, and the relative error was almost 0%.
The input signal to be measured corresponding to fig. 32 is a common amplitude modulation wave with carrier frequency of 30MHz, modulation signal frequency of 2kHz and amplitude modulation index of 0.2 (the modulation signal is a sine wave). The liquid crystal screen of the measuring system displays an automatic measuring result, the modulation type is judged to be a single-tone modulated amplitude modulation wave, the frequency of a modulation signal is 2.016kHz, the amplitude modulation index is 0.215, and meanwhile, information such as a waveform chart, a modulation signal spectrogram and the like which are output by demodulation of the amplitude modulation wave is displayed. From the measurement data displayed on the screen, the modulation type is judged correctly, the frequency of the measured demodulation signal is 2.016kHz, and the relative error of frequency measurement is 0.8%; the amplitude modulation index was measured to be 0.215 and the relative error was 7.5%.
The measurement result shows that the system judges the type of the common amplitude modulation wave (AM wave) input into the single frequency modulation to be measured (the modulation signal is sine wave), and the measured amplitude modulation index m a The maximum relative error was 7.5%. The measured demodulation signal frequency relative error maximum was 0.8%. The data record results of multiple experimental tests on different carrier frequencies and modulation parameters are shown in the measurement data table of fig. 27, the system judges the type of the input to-be-detected common amplitude modulation wave correctly, the measurement accuracy of the amplitude modulation wave parameters is higher, and the maximum measurement errors of the carrier signal frequency and the amplitude modulation index are within 8% for the continuous 10 measurement results of the same amplitude modulation wave parameters.
The input signal to be measured corresponding to fig. 33 is a frequency modulated wave (FM wave) with a carrier frequency of 10MHz, a modulated signal frequency of 10kHz, and a frequency modulation index of 6, and a single frequency modulation (modulated signal is a sine wave) with a maximum frequency offset of 60 kHz. The liquid crystal screen of the measuring system displays an automatic measuring result, the modulation type is judged to be FM wave, the frequency of a modulation signal is 10.019kHz, the frequency modulation index is 5.915, and the maximumThe frequency offset is 59.265kHz, and information such as a waveform diagram, a modulation signal spectrogram and the like of FM wave demodulation output are displayed. From the measurement data displayed on the screen, the modulation type is judged correctly, the measured carrier signal frequency is 10000KHz, namely 10MHz, and the relative error is almost equal; the measured demodulation signal frequency is 10.019kHz, and the relative error of frequency measurement is 0.19%; frequency modulation index m f Is 5.915, the relative error is 1.42%, and the maximum frequency deviation delta f m The measurement result of (2) was 59.265kHz, and the relative error was 1.23%.
The input signal to be measured corresponding to fig. 34 is a carrier frequency of 30MHz, the frequency of the modulated signal is 3kHz, the frequency modulation index is 1, and the signal corresponds to a single-frequency modulated (modulated signal is a sine wave) frequency modulation wave (FM wave) with a maximum frequency offset of 3 kHz. The liquid crystal screen of the measuring system displays an automatic measuring result, the modulation type is judged to be FM wave, the frequency of the modulation signal is 3.024kHz, and the frequency modulation index m f Is 0.996, the maximum frequency deviation delta f m The frequency spectrum is 3.012kHz, and information such as a waveform chart, a modulation signal spectrum chart and the like of the FM wave demodulation output are displayed at the same time. As can be seen from the measurement data displayed on the screen, the modulation type is judged correctly, the measured carrier signal frequency is 30000KHz, namely 30MHz, and the relative error is almost 0%; the frequency of the measured demodulation signal is 3.024kHz, and the relative error of frequency measurement is 0.8%; frequency modulation index m f Is measured to be 0.996, the relative error is 0.4%, and the maximum frequency deviation deltaf is calculated m The measurement result of (2) was 3.012kHz, and the relative error was 0.4%.
The measurement result shows that the system judges the type of the frequency modulation wave input into the single-frequency modulation to be measured (the modulation signal is sine wave) correctly, and the relative error of the measured carrier frequency is almost 0%; the measured demodulation signal frequency relative error maximum value is 0.4%; measured frequency modulation index m f The maximum relative error is 1.42%. Maximum frequency offset Δf measured m The maximum relative error is 1.23%. Through multiple tests, the device can judge the type of the frequency modulation wave of the single-frequency modulation (the modulation signal is sine wave) to be input and tested correctly, the measurement precision of the frequency modulation wave parameter is higher, and the measurement error of the main modulation parameter is basically within 5%.
The input signal to be measured corresponding to fig. 35 is an unmodulated single frequency continuous carrier signal with a carrier frequency of 10MHz. The liquid crystal screen of the measuring system displays an automatic measuring result, the modulation type is judged to be an unmodulated single-frequency continuous carrier signal, and the carrier signal frequency is 10000KHz, namely 10MHz. The measured data displayed on the screen can be seen that the modulation type is judged correctly, and the measured carrier signal frequency error is almost 0%.
The input signal to be measured corresponding to fig. 36 is an unmodulated single frequency continuous carrier signal with a carrier frequency of 30MHz. The liquid crystal screen of the measuring system displays an automatic measuring result, the modulation type is judged to be an unmodulated single-frequency continuous carrier signal, and the carrier signal frequency is 30000KHz, namely 30MHz. The measured data displayed on the screen can be seen that the modulation type is judged correctly, and the measured carrier signal frequency error is zero.
The measurement result shows that the system judges the type of the input to-be-measured unmodulated single-frequency continuous carrier signal correctly, and the relative error of the measured carrier frequency is almost 0%.
31-36, it can be shown from the modulation type judgment and parameter measurement results that the device judges the types of the three signals of the normal amplitude modulation wave (AM wave) input with the single-frequency modulation to be detected (the modulation signal is a sine wave), the frequency modulation wave (FM wave) with the single-frequency modulation (the modulation signal is a sine wave) and the unmodulated single-frequency continuous carrier signal correctly; the measured frequency of the demodulation signal of the AM wave is 2.4% of the maximum value of the relative error, and the measured frequency of the demodulation signal of the FM wave is 2.0% of the maximum value of the relative error; measured amplitude modulation index m a The maximum value of the relative error is 8.0%, and the measured frequency modulation index m f The maximum value of the relative error is 3.2%; the maximum measurement error of the carrier signal frequency of the measured single-frequency modulated (the modulated signal is a sine wave) FM wave is almost 0%; the carrier frequency error of the measured, unmodulated, single frequency continuous carrier signal is almost 0%.
Tables 1 and 2 show the results of multiple actual measurements of the automatic identification of the modulation type of the radio signal and the automatic measurement system of the modulation parameters.
TABLE 1
TABLE 2
Table 1 shows the automatic measurement results displayed on the LCD screen of the measurement system when the input signal to be measured is AM wave with carrier frequency of 20MHz (the modulated signal is sine wave) and the amplitude modulation indexes are respectively 0.2, 0.4, 0.6, 0.8 and 1, and the corresponding modulated signal frequencies are respectively 2kHz, 3.5KHz and 5KHz, and the automatic measurement results comprise carrier frequency and amplitude modulation index and the maximum parameter error of continuous 10-time measurement of the amplitude modulation signals of the same group of parameters. The measurement result shows that the system judges the type of the AM wave to be input and measured correctly, and the frequency relative error maximum value of the AM wave demodulation signal is 2.4% and the measured amplitude modulation index m is the result of continuous 10 times of measurement of the amplitude modulation signal with the same parameter a The maximum relative error is 8.0%.
Table 2 shows the automatic measurement results displayed on the LCD screen of the measurement system when the input signal to be measured is the FM wave of single frequency modulation (the modulation signal is sine wave) with the carrier frequency of 20MHz and the frequency modulation indexes are respectively 1, 2, 3.5, 5 and 6, and the corresponding modulation signal frequencies are respectively 3kHz, 6KHz and 10KHz, and the automatic measurement results comprise the carrier frequency, the frequency modulation index and the maximum parameter error of continuous 10-time measurement of the frequency modulation signals with the same group of parameters. The measurement result shows that the system judges the type of the FM wave to be input and measured correctly, and the frequency modulation index m is measured by continuously measuring the FM signal of the same parameter for 10 times, wherein the maximum value of the frequency relative error of the FM wave demodulation signal is 2.0 percent f The maximum relative error is 3.2%.
The technical scheme of the invention is not limited to the embodiments, and all technical schemes obtained by adopting equivalent substitution modes fall within the scope of the invention.

Claims (9)

1. An automatic measurement system for modulation parameters of a radio signal, comprising:
the local oscillation signal source circuit module outputs local oscillation signals containing single-frequency sine wave signals and sine wave signals with continuous sweep frequency based on the DDS;
an envelope detection circuit module for demodulating the common amplitude-modulated wave signal modulated by a single frequency,
the stereo modulation-demodulation circuit module is used for demodulating a single-frequency modulated frequency-modulated wave signal with fixed carrier frequency, and the high-speed electronic switch circuit module is used for switching the signal to be detected to be input into an amplitude modulation wave demodulation channel or a frequency modulation wave demodulation channel; switching the demodulated amplitude modulation wave signal or frequency modulation wave signal to enter an output channel; switching the baseband signal after the radio signal to be tested is mixed or the demodulation signal of the amplitude modulation wave signal or the frequency modulation wave signal in the output channel to carry out ADC sampling,
the active mixer circuit module comprises a mixer, wherein the mixer is used for completing the mixing of an input radio signal to be detected and a local oscillator signal and shifting the frequency spectrum and carrier frequency of the input radio signal to be detected;
The passive high-pass filter circuit module is used as a frequency-selecting filter for inputting the single-frequency modulated frequency-modulated wave signals to be detected after mixing, and the frequency-modulated wave signals after up-conversion are input into the stereo frequency-modulation demodulation module;
the singlechip is used for controlling the DDS to generate a local oscillation signal; the high-speed electronic switch is controlled to carry out ADC sampling and gate an amplitude modulation wave demodulation channel or a frequency modulation wave demodulation channel; the calculation includes: modulation parameters of frequency, spectrum, amplitude modulation index of amplitude modulated signal and frequency modulation index of frequency modulated wave; and judging the modulation type of the signal to be detected, and tracking and measuring the carrier frequency of the single-frequency modulated frequency modulation wave and the carrier frequency of the single-frequency continuous carrier signal which is not modulated.
2. The automatic measurement system of modulation parameters of a radio signal according to claim 1, further comprising:
and the intermediate frequency amplifier circuit module amplifies the input to-be-detected single-frequency modulated common amplitude-modulated wave signal to enable the amplitude of the input to-be-detected amplitude-modulated wave signal to meet the requirement of the input level of the envelope detection module.
3. The automatic measurement system of modulation parameters of a radio signal according to claim 1, further comprising: the first active low-pass filter circuit is used as a filter of a baseband signal, and the baseband signal is obtained by down-converting an externally input frequency-modulated wave signal to be detected with single frequency modulation through a mixer and a local oscillator signal.
4. The automatic measurement system of modulation parameters of a radio signal according to claim 1, further comprising: and the second active low-pass filter circuit module is used for carrying out low-frequency filtering on the modulated signals demodulated and output by the envelope detection module and the stereo tone demodulation module, and filtering out high-frequency components and noise.
5. The automatic measurement system of modulation parameters of a radio signal according to claim 1, further comprising: and the low-frequency amplifier circuit module amplifies the baseband signal after the down-conversion of the mixer and the modulation signal demodulated and output by the stereo modulation circuit module.
6. The automatic measurement system for modulation parameters of a radio signal according to claim 1, wherein a superheterodyne structure is used to shift and down-convert a frequency spectrum of a signal to be measured to a baseband, and a singlechip is used to sample the down-converted signal, and FFT conversion is performed to obtain a frequency spectrum characteristic of the signal.
7. The automatic measurement system for modulation parameters of a radio signal according to claim 1, wherein the single chip microcomputer judges the modulation type of the signal to be measured and tracks and measures the carrier frequencies of the single frequency modulated frequency modulation wave and the unmodulated single frequency continuous carrier signal:
The radio signal to be tested enters an amplitude modulation wave demodulation channel through an electronic switch, the output of an envelope detection circuit is sent to a singlechip for sampling, and if the sampled signal is a standard single-frequency sine wave periodic signal, the input signal is judged to be a common amplitude modulation wave modulated by single frequency;
if the signal is not sinusoidal, inputting the signal to be detected into a frequency modulation wave demodulation channel through an electronic switch again, and judging the type of the frequency modulation wave and measuring the carrier frequency;
in the process of local oscillation signal frequency sweep, corresponding to each frequency point of local oscillation signal, a singlechip performs FFT conversion on a sampling signal to obtain spectrum information of a radio signal to be tested after down conversion, then performs FFT conversion according to the signal after down conversion sampled by the singlechip to analyze main characteristics of a spectrum, if in the process of frequency sweep, corresponding to a certain frequency of the local oscillation signal, the spectrum obtained by FFT conversion of the sampling signal at least contains two or more frequency spectrum components near zero frequency, then judges that the radio signal to be tested is a single-frequency modulated frequency modulation wave, and records the corresponding local oscillation signal frequency f at the moment according to spectrum characteristic analysis when the frequency of the local oscillation signal is the same as the carrier frequency of the frequency modulation wave to be tested 0 ，f 0 Is the carrier frequency of the frequency modulation wave to be measured.
If the frequency spectrum obtained by FFT conversion of the sampling signal does not have at least two frequency components with larger amplitude near zero frequency after the local oscillation signal passes through a complete round of frequency sweep, the signal to be detected is not a frequency modulation wave, and the signal to be detected is an unmodulated single-frequency continuous carrier signal.
8. The automatic measurement system for modulation parameters of radio signal according to claim 1, wherein said single-chip microcomputer calculates an amplitude modulation index m of a common amplitude-modulated wave of single-tone modulation a The specific process is as follows:
1) Amplitude modulation index m of common amplitude modulation wave a Is calculated by (1):
the single frequency modulated AM wave can be described by the mathematical expression:
in the method, in the process of the invention,called amplitude modulation index or amplitude modulation, k a Representing the sensitivity of amplitude modulation, V 0 Representing the amplitude of the unmodulated carrier, V Ω Representing the amplitude of the modulated signal;
can be deduced from the formula (1)
V max And V min Respectively representing the maximum value and the minimum value of the amplitude modulation wave envelope;
the voltage transmission coefficient K of the envelope detection circuit is determined in advance by utilizing the characteristic that the voltage transmission coefficient of the envelope detection circuit is basically unchanged (the voltage transmission coefficient is defined as the amplitude of a demodulation signal/the amplitude of an input amplitude modulation wave envelope) d Sampling and measuring demodulation waveform amplitude U by using single chip microcomputer Ω According to the formula (3), the envelope amplitude m converted into a normal amplitude-modulated wave a Vim, the amplitude modulation index m of the amplitude modulation wave to be measured can be calculated a 。
Wherein K is d U is the voltage transmission coefficient of the detector Ω For the output voltage of the envelope detection circuit, m a For amplitude modulation index, U i Is the amplitude of the carrier voltage.
9. The system for automatically measuring modulation parameters of a radio signal according to claim 1, wherein said single-chip microcomputer
Calculating the frequency modulation index m of the frequency modulation wave to be measured f Maximum frequency offset Δf m The method specifically comprises the following steps:
step 1), measuring a frequency discrimination S curve of the stereo frequency modulation demodulation circuit in advance according to the characteristic that the slope of the frequency discrimination S curve of the stereo frequency modulation demodulation circuit is basically unchanged in a linear region;
step 2) calculating the slope of the frequency discrimination S curve, namely the frequency discrimination sensitivity k of the stereo tone demodulation circuit f The single chip microcomputer samples and measures the voltage amplitude V of the output waveform of the frequency discriminator m Calculating the frequency f of the modulated signal, which is the demodulation waveform, by FFT m According to the frequency discrimination sensitivity k f Calculating the maximum frequency deviation delta f of the corresponding frequency modulation wave to be detected according to the formula (4) m ；
Calculating a frequency modulation index m corresponding to the frequency modulation wave to be measured according to the step (5) f 。
CN202310541605.0A 2023-05-12 2023-05-12 Automatic measurement system for modulation parameters of radio signals Pending CN116506035A (en)

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