Design of an analogue modulation parameter measuring system for radio signals
The measurement of analog modulation parameters of radio signals has extensive applications in various fields,including radio detection and positioning,communication transmitter testing and calibration,and navigation communication of civil ships.An analogue modulation parameter measuring system for radio signal is designed and realized.STM32F4 series microcontroller is used as the control core of the system and superheterodyne structure is adopted.The main hardware circuit modules consist of a local oscillator signal source,mixer,LC passive filter,phase-locked loop,low-noise amplifier,envelope detection circuit and frequency discriminator circuit.This system is capable of automatically identify analog modulation types such as ordinary amplitude modulation,frequency modulation,and unmodulated single-frequency carrier.It can also automatically measure major modulation parameters including carrier frequency,modulation signal frequency,modulation index,and maximum frequency deviation of the carrier.The experimental results demonstrate modulation types can be accurately identified.Moreover,the demodulated waveform of both amplitude and frequency modulated signals exhibits a high signal-to-noise ratio and no obviously distortion.Furthermore,the relative error of measuring the carrier frequency is less than 10-5,while the relative error of measuring the main modulation parameter is less than 5%.
radio signalcarrier frequencymodulation type identificationmodulation parameter measurement
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