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Luku 2 – Tietoliikenteen tekniikka

Luku 2 – Tietoliikenteen tekniikka. OSA 1: Analogisen tiedon siirto, Analoginen siirtotie OSA 2: Digitaalinen siirtotie OSA 3: Johdolliset siirtotiet (optinen kuitu). Luku 2 – Tietoliikenteen tekniikka. v Modem - ModulatorDemodulator.

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Luku 2 – Tietoliikenteen tekniikka

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  1. Luku 2 – Tietoliikenteen tekniikka OSA 1: Analogisen tiedon siirto, Analoginen siirtotie OSA 2: Digitaalinen siirtotie OSA 3: Johdolliset siirtotiet (optinen kuitu) TLTP/AVi Luku 2

  2. Luku 2 – Tietoliikenteen tekniikka TLTP/AVi Luku 2

  3. vModem - ModulatorDemodulator FMuuntaadigitaalisensignaalinsellaiseksi, että se soveltuuanalogisellesiirtotielle FMuuntaa analogisen siirtotien signaali digitaaliseen muotoon FKoskadigitaalistasignaalia (kanttiaalto!) eiyleensäsiirretäsellaisenaan, läheskaikkitietoliikenne on tavalla tai toisellamoduloitu FAinoamoduloimatonsiirtotapahtuukuiduissa. Luku 2 - Modulointi TLTP/AVi Luku 2

  4. Luku 2 – Modulointi TLTP/AVi Luku 2

  5. Luku 2 - Modulointi TLTP/AVi Luku 2

  6. Luku 2 - Perinteisetanalogisetmodulointimenetelmät TLTP/AVi Luku 2

  7. Luku 2 – Amplitudimodulointi AM TLTP/AVi Luku 2

  8. Luku 2 – Taajuusmodulointi FM TLTP/AVi Luku 2

  9. Luku 2 – Vaihemodulointi PM Figure 5.20 Phase modulation TLTP/AVi Luku 2

  10. Luku 2 – Amplitudimodulointi AM • Modulaatioindeksi eli modulaation”syvyys” • Teho - TLTP/AVi Luku 2

  11. Luku 2 - AM - TLTP/AVi Luku 2

  12. Luku 2 – AM-spektri • Harj 1. Piirrä DSB-AM –modulaation spektri, kun kantataajuus on 3 kHz 5 V ja moduloitavan kantoaallon taajuus on 100 kHz ja sen signaalin amplitudi on 15 V. Mitkä ovat syntyneet taajuuskomponentit? • Harj. 2. Selvitä oheisen AM-spektrin modulaatioindeksi, kantataajuus fm P/dBm 3 2 1 f/Hz fLSB fc fUSB 1: -60dBm, 100,003MHz 2: -60dBm, 99,997MHz 3: -40dBm, 100,000MHz TLTP/AVi Luku 2

  13. FM Modulation Index • The modulation index for a FM signal is defined as the ratio of the maximum frequency deviation to the modulating signal’s frequency. It is given by TLTP/AVi Luku 2

  14. FM Frequency Analysis • Analysis of the frequency components and their respective amplitude in the FM wave requires use of a complex mathematical integral known as the Bessel function of the first kind of the n-th order. Actually, Bessel function generates an infinite sideband of a FM signal, which can be represented as TLTP/AVi Luku 2

  15. FM Frequency Analysis • So, actually the FM wave contains an infinite number of sidebands. Each set of upper and lower sideband is displaced from the carrier frequency by an integer multipal of the modulation frequency: n × fm, where n=1,2,3,… . • From the Bessel functions, we can get some conclusions: • As the modulation index increases from zero, the spectral energy shifts from the carrier frequency to an increasing number of significant sidebands. It means the wider bandwidth is required to carrier the FM signal. • The magnitudes of the sideband amplitudes J decrease in value with increasing order n. TLTP/AVi Luku 2

  16. Bessel Table • Bessel Function needs complex differentials and integrals, usually a table is used by the engineers. TLTP/AVi Luku 2

  17. FM Frequency Analysis J1=0.58 J1=0.58 J2=0.35 J2=0.35 J0=0.22 J3=0.13 J3=0.13 fm J4=0.03 J4=0.03 Freq. J5=0.01 J5=0.01 fc m=2 TLTP/AVi Luku 2

  18. Luku 2 - The Frequency Modulation FM Example 4.1 Find the carrier and sidebandamplitudes to the 4th-order sideband for a modulationindexmf = 3. The peakamplitude of the carrierVc is 10V. Example 4.2 Frequencydeviation Modulationfrequencyfm TLTP/AVi Luku 2

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