AM – DSB-SC (double sideband suppressed carrier)

Modulatorthe modulated signal.AM – DSB-SC (double sideband suppressed carrier)SpectrumM ( f ) = F [m(t )] S ( f ) = F [m(t ) cos(2π f 0 t )] = F [m(t )] ∗ F [cos(2π f 0 t )] = = M ( f ) ∗ 1 [δ ( f − f 0 ) + δ ( f + f 0 )] = 2 = 1 M ( f − f0 ) + 1 M ( f + f0 ) 2 2.AM – DSB-SC (double sideband suppressed carrier)fMPower of the modulating signalP=∫| M ( f ) |2 dfS =...
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AM – DSB-SC (double sideband suppressed carrier) AM – DSB-SC (double sideband suppressed carrier)Modulatorthe modulatedsignal AM – DSB-SC (double sideband suppressed carrier) M ( f ) = F [m(t )]Spectrum S ( f ) = F [m(t ) cos(2π f 0 t )] = F [m(t )] ∗ F [cos(2π f 0 t )] = = M ( f ) ∗ 1 [δ ( f − f 0 ) + δ ( f + f 0 )] = 2 = 1 M ( f − f0 ) + 1 M ( f + f0 ) 2 2 AM – DSB-SC (double sideband suppressed carrier) fM ∫ | M ( f ) |2 df P=Power of the modulating signal − fM S = ∫ | S ( f ) |2 df = 1 P + 1 P = 1 PPower of the modulated signal (DSB-SC) 4 4 2 (if the amplitude of the carrier signal =1) AM – DSB-SC (double sideband suppressed carrier)Practical method of DSB-SC generation x(t ) = m(t ) [a1 cos(2π f 0t ) + a3 cos(2π 3 f 0t ) + a5 cos(2π 5 f 0t ) + …] = = a1m(t ) cos(2π f 0t ) + a3m(t )cos(2π 3 f 0t ) + a5 m(t )cos(2π 5 f 0t ) + … DSB-SC, carrier f0 DSB-SC, carrier 3f0 DSB-SC, carrier 5f0 AM – DSB-SC (double sideband suppressed carrier)The high – frequency components may be eliminated, using a filter: s (t ) = a1 m(t ) cos(2π f 0 t ) At the filter output: AM – DSB-SC: demodulatorReceiver with a synchronous detector band- low- pass pass filter filter DSBSC +noise bandwidth fM bandwidth B synchronous detector1. DSC-SC signal without noise s (t ) = m(t ) cos(2π f 0 t ) - input of the synchronous detector: m(t ) cos 2 (2π f 0 t ) = m(t ) [ 1 + 1 cos(4π f 0 t )] - output of the synchronous detector : 2 2 s0 (t ) = 1 m(t ), =1P power S 0 moc - output of the low-pass filter: 2 4 AM – DSB-SC: demodulator P S P SNR0 = 0 = 4 =2. signal to noise ratio at the output of the receiver N 0 η f M 2η f M P 2 S P =2= at the output of the channel SNR = = SNR0 N η f M 2η f M B   f fM SNR0,max = 1 + M SNR  −1 maximum resistance to channel noise   B 2 SNR0,max = [1 + 1 SNR ] − 1 > SNR0, DSBSC Here, bandwidth expansion B/fM =2 2 DSBSC receiver with a synchronous detector does not attain maximum resistance to channel noise Application of the AM – DSB-SC: the analog stereo signalL(t), R(t) – left and right channelThe composite stereo signal: f0 m(t ) = [ L(t ) + R(t )] + [ L(t ) − R (t )]cos(2π f 0t ) + a cos(2π t) ...