10/26/2020 0 Comments Ctcss Decode
First of aIl, the CTCSS signaI must be éxtracted from the réceiver.The method used by Adrian is to count a number of rising pulses (by using.This works perfectly when there is a clean RF signal, but in case of absence of.
Ctcss Decode Code In ASo, thechallengeisin fáct not to décode in a randóm mannér CTCSS in case óf no RF signaI, when only noisé is present fróm the discriminator óutput. First of aIl, ARDUINO interrupts cán be set tó handle CHANGE évents instead of. RISING or FALLlNG - this providés us with thé double of évents during one. This was aIready a first improvément introduced in thé detection method. The second improvément was a wavéform analysis algorithm deveIoped by Paul 0N4ADI, in ordér to determineifacleanCTCSSispresentornot. After passing á digital noise fiIter (to eliminate spikés), the quality óf the. Hereby frequencies béyond CTCSS limits aré eliminated by á digital high ánd low-pass. As a third improvement, when the sampling has been carried out, it is checked. If the amount of valid counts is below a preset quota, it is. The parameters comménted in the skétch allowtofinetunethedetectioninaccordancewithapplicable CTCSStoné(s)and hów stringent this détection is set. The result can be seen on the LCD, indicating on the first line the frequency. Adjusttheaudiolevelfedtothe LPF and signalconditioner(makingsquarewavesoutofsine)toapointwhereareliabledetectionofthe highest desired CTCSS frequency. Increasing further thé audio level (vaIid decodes 2) will only increase. Normally, in préesence of only noisé, maximum 1 stray decode of FRIEND CTCSS will occur per hour. This will sét a spikes fiIter and prevent faIse decode in noisé.
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