1. Error in synchronous Demodulator ระบบวิทยุ (Radio System) 252442 ผู้ช่วยศาสตราจารย์ธราดล โกมลมิศร์ ภาควิชาวิศวกรรมไฟฟ้า คณะวิศวกรรมศาสตร์ มหาวิทยาลัยเชียงใหม่

2. Error in Synchronous Demodulator 2 กำหนดให้  Carrier (f c =100,000Hz) Cos2  f c t = Cos2  100,000t  Modulating signal (f m =1,000Hz) Cos2  f m t = Cos2  1,000t  DSB-SC Modulated signal Cos2  f c tCos2  f m t = Cos2  100,000tCos2  1,000t = 0.5Cos2  101,000t+0.5Cos2  99,000t = 0.5Cos2  101,000t+0.5Cos2  99,000t  SSB Modulated signal (USB) 0.5Cos2  101,000t  SSB Modulated signal (LSB) 0.5Cos2  99,000t

3. Error in Synchronous Demodulator 3 No error f LO =f C : DSB-SC  Local Oscillator = Cos2  100,000t  Demodulated signal for DSB-SC (before LPF) (0.5Cos2  101,000t+0.5Cos2  99,000t)Cos2  100,000t(0.5Cos2  101,000t+0.5Cos2  99,000t)Cos2  100,000t 0.5Cos2  101,000tCos2  100,000t +0.5Cos2  99,000tCos2  100,000t 0.5Cos2  101,000tCos2  100,000t +0.5Cos2  99,000tCos2  100,000t 0.25Cos2  201,000t + 0.25Cos2  1,000t +0.25Cos2  199,000t + 0.25Cos(-2  1,000t) 0.25Cos2  201,000t + 0.25Cos2  1,000t +0.25Cos2  199,000t + 0.25Cos(-2  1,000t)  Demodulated signal for DSB-SC (After LPF) 0.25Cos2  1,000t + 0.25Cos2  1,000t = 0.5Cos2  1,000t0.25Cos2  1,000t + 0.25Cos2  1,000t = 0.5Cos2  1,000t

4. Error in Synchronous Demodulator 4 No error f LO =f C : DSB-SC  Spectrum (before LPF)  Spectrum (after LPF)  Signal (after LPF) f 201,00 0 199,00 0 1,000 - 1,00 0 - 199,00 0 - 201,00 0 f 1,000 - 1,00 0 1,000 Hz (ok)

5. Error in Synchronous Demodulator 5 No error f LO =f C : SSB-USB  Local Oscillator = Cos2  100,000t  Demodulated signal for SSB-USB (before LPF) = 0.5Cos2  101,000tCos2  100,000t =0.25Cos2  201,000t + 0.25Cos2  1,000t  Demodulated signal for SSB-USB (After LPF) = 0.25Cos2  1,000t

6. Error in Synchronous Demodulator 6 No error f LO =f C : SSB-USB  Spectrum (before LPF)  Spectrum (after LPF)  Signal (after LPF) f 201,00 0 1,000 - 1,00 0 - 201,00 0 f 1,000 - 1,00 0 1,000 Hz (ok)

7. Error in Synchronous Demodulator 7 Frequency error  f= +1 Hz : DSB-SC  Local Oscillator = Cos2  100,001t  Demodulated signal for DSB-SC (before LPF) =(0.5Cos2  101,000t+0.5Cos2  99,000t)Cos2  100,001t = 0.5Cos2  101,000tCos2  100,001t +0.5Cos2  99,000tCos2  100,001t = 0.25Cos2  201,001t + 0.25Cos2  999t +0.25Cos2  199,001t + 0.25Cos2  1,001t  Demodulated signal for DSB-SC (After LPF) = 0.25Cos2  999t + 0.25Cos2  1,001t = 0.5Cos2  1,000tCos2  1t

8. Error in Synchronous Demodulator 8 Frequency error  f= +1 Hz : DSB-SC  Spectrum (before LPF)  Spectrum (after LPF)  Signal (after LPF) f 201,00 1 199,00 1 999 1,001 -1,001 -999 - 199,00 1 - 201,00 1 f 999 1,001 -1,001 -999 1 Hz 1,000 Hz

9. Error in Synchronous Demodulator 9 Frequency error  f= +1 Hz : SSB-USB  Local Oscillator = Cos2  100,001t  Demodulated signal for SSB-USB (before LPF) =0.5Cos2  101,000tCos2  100,001t =0.25Cos2  201,001t + 0.25Cos2  999t  Demodulated signal for SSB-USB (After LPF) = 0.25Cos2  999t

10. Error in Synchronous Demodulator 10 Frequency error  f= +1 Hz : SSB-USB  Spectrum (before LPF)  Spectrum (after LPF)  Signal (after LPF) f 201,00 1 999 - 999 - 201,00 1 f 999 - 999 999 Hz (frequency change)

11. Error in Synchronous Demodulator 11 Phase error  =  /4 : DSB-SC  Local Oscillator = Cos(2  100,000t+  /4)  Demodulated signal for DSB-SC (before LPF) =(0.5Cos2  101,000t+0.5Cos2  99,000t)Cos(2  100,000t+  /4) = 0.5Cos2  101,000tCos(2  100,000t +  /4) +0.5Cos2  99,000tCos(2  100,000t +  /4) = 0.25Cos(2  201,000t+  /4) + 0.25Cos(2  1,000t-  /4) +0.25Cos(2  199,000t+  /4) + 0.25Cos(-2  1,000t-  /4)  Demodulated signal for DSB-SC (After LPF) = 0.25Cos(2  1,000t-  /4) + 0.25Cos(2  1,000t+  /4) = 0.5Cos2  1,000tCos  /4 = 0.707x0.5Cos2  1,000t

12. Error in Synchronous Demodulator 12 Phase error  =  /4 : DSB-SC  Spectrum (before LPF)  Spectrum (after LPF)  Signal (after LPF) f 201,00 0 199,00 0 1,000 - 1,00 0 - 199,00 0 - 201,00 0 f 1,000 - 1,000 1kHz (amplitude drop)

13. Error in Synchronous Demodulator 13 Phase error  =  /4 : SSB-USB  Local Oscillator = Cos(2  100,000t+  /4)  Demodulated signal for DSB-SC (before LPF) = 0.5Cos2  101,000tCos(2  100,000t +  /4) = 0.25Cos(2  201,000t+  /4) + 0.25Cos(2  1,000t-  /4)  Demodulated signal for DSB-SC (After LPF) = 0.25Cos(2  1,000t-  /4)

14. Error in Synchronous Demodulator 14 Phase error  =  /4 : SSB-USB  Spectrum (before LPF)  Spectrum (after LPF)  Signal (after LPF) f 201,00 0 1,000 - 1,00 0 - 201,00 0 f 1,000 - 1,00 0 1kHz(shift phase)