Research And Implementation Of Short-wave Transmitter Front-end Filter Circuitry

Shortwave communication is a long distance signal transmission which mainly relies on the reflection between the ionosphere and the ground.It has the advantages of achieving strong maneuverability,long communication distance,no need to build a relay station to realize long distance communication,and it has been widely used in various fields of the national economy.There is an important application value especially in disaster relief,military communications,emergency communications and remote mountainous areas.Transmitter is an important part of shortwave communication systems,in order to adapt to the development of modern short wave radio communication new technology such as real-time frequency selection,adaptive frequency hopping,and transmitter power amplifier circuit using broadband amplifier circuit.There are higher requirements in flatness,frequency spectrum and the stability of the signal.Filter circuit includes front-end digital pre-selection filter and back-end piecewise filter,the development of high flatness,high frequency spectral purity shortwave transmitter front-end filtering circuit is the key point to improving the performance of shortwave communication system.Firstly,this paper provides an overview of the research background,significance and research status at home and abroad of the short wave communication,pre-selection and segmented filter;further introduce the structure of shortwave transmitter front-end circuit,discusses the performance indicators on the filter and broadband RF power amplifier circuit.Secondly,based on further research on the theory of radio frequency filtering,design digital pre-selection filter circuit comprising the programming filter and variable gain amplifier,which can filter out the spurious distortion components of input modulated signal,and do the pre amplification which can preset gain to the signal,in order to meet the requirements of high flatness in short wave frequency band.Then introduces the RF power amplifier circuit as an important part of the short wave emission front-end circuit,and design circuit for each module of broadband power amplifier.Finally,emphasis on the design and implementation of the segmented filter circuit in short wave emission front-end circuit.The working frequency band of the pre-selection,segmented filter circuit designed in this paper is1.5~30MHz,and the frequency domain is wider.According to the requirements of high flatness,high frequency spectrum purity,focus on the design of 6 band sub harmonic filter,through the ADS simulation and theoretical analysis on the 6 band filter unit circuit,use the 7 order elliptic low-pass filter with good cut-off characteristic to design filter unit circuit.Segmented sub harmonic filter filtering out high order harmonic wave,cross modulation component and out of band interference in 1.5~30MHz output signal,obtain the circuit schematic which meets the design requirements.Successfully make the material object of the short wave transmission front-end segmented filter circuit according to the circuit schematic diagram,finally test the relative performance on the material object of the segmented sub harmonic frequency filter circuit,the test data meets the design requirements.