Design And Implementation Of Radio Frequency Circuit In Short Wave Medium Frequency Digital Platform

Using the idea of software radio,a kind of wireless communication equipment which can realize multi-band and multi-function can be realized by software setting.It is of great significance to realize the interconnection between various military forces and departments on the battlefield.The concept of designing a software radio digital receiver is to make broadband A/D conversion as close as possible to the RF end sampling,and the subsequent processing is all completed by the digital signal processing platform.However,at this stage,the manufacturing technology level of the anti-aliasing filter and the broadband A/D conversion chip,and operational capability are limited.The short wave digital communication could not achieve the required sensitivity in direct sampling at the RF end.Therefore,the scheme adopted in the practical application is to transform the generated intermediate frequency signals after the analog channel mixing to carry out the A/D transformation,and then give the subsequent digital signal processing link to process,and finally complete the short wave reception function.The RF analog mixing circuit designed in this paper is used in the short wave medium frequency digital communication platform to realize the functions of radio frequency signal reception,excitation signal generation and fault self-detection in short wave communication.The RF circuit is a key component of the analog channel,and many technical indicators of the radio are closely related to it.The RF circuit designed in this paper mainly improves the sensitivity of RF receiving circuit and extends its dynamic range in performance.It mainly studies the design and principle of analog mixing,amplification and filtering circuits in RF transceiver channel.The noise theory,sensitivity calculation and AGC control principle of RF receiving circuit are discussed in theory.In the circuit design,the detailed principle design of the main functional circuits,such as the receiving circuit,the AGC control circuit,the excitation circuit,the self-checking circuit and the transceiver circuit,is given.The RF circuit designed in this paper works in the short wave band(2MHz to 30MHz).The receiving function circuit uses a new type of low noise amplifier and narrow band crystal filter.The noise coefficient of the receiving circuit is about 12,which makes the sensitivity index of the receiving circuit up to-113 dBm.The introduction of AGC control circuit enables the dynamic range of the receiving circuit to reach 80 dB.The excitation function circuit outputs the intermediate frequency signal input from the medium frequency digital processing platform after filtering,amplifying,mixing and other processing.The RF excitation signal is output,and the power amplifier is provided to the short wave power amplifier for the back end.The output signal power is 7dBm ± 2dB.The intra band inter modulation index is up to-53 dB.In the early stage of the circuit design,the theoretical feasibility analysis,the selected circuit scheme,the design circuit principle,the selection of components or the need to customize the relevant devices according to the circuit design,and the reasonable PCB design and other work are the guarantee of the successful development of the paper.Through testing the assembled RF circuits,the results show that all the indexes of the RF circuit satisfy the interface index requirements of the intermediate frequency digital platform.In the end,the fault mode of the circuit is analyzed,and the fault and the degree of damage which are easy to happen in the production and application are found,and the productivity of the circuit is improved.