The Realizing Of Continuous Tone Controlled Squelch System Using DSP

Continuous Tone Controlled Squelch System(CTCSS) is a technology which transmit sub-audio fequency siginal with audio frequency siginal to squelch or multi-use the same fequency channel and it is widely usede in various wireless communication facility.CTCSS was realized by special chips before and the method is gradually abandoned when the currency chip DSP is developed with high speed and greatly proved in performance.Therefore,it has important meaning to realize CTCSS by DSP.First,this thesis introduces basic concept of Continuous Tone Controlled Squelch System and the reason using DSP replacing special chip to realize it.And how to choice the DSP chip is introduced.Secondly, the function and the interface of the DSP system is confirmed by analyzing the function and the structure of original squelch system.On this basis,each part of the DSP system's circuit is designed and the working state of the DSP is confirmed.Thirdly,the basic theory of the Geotzel arithmetic used in decoding sub-audio is introduced.The arithmetic is improved on this system.Some problem which must be solved in the realizing of the arithmetic is described in this thesis.How to design software on the DSP system is analyzed on the basis of the above article.The main work of the software is coding and decoding the sub-audio.Finally,how to design the bootloading process of the DSP system is introduced.