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1 Single Side Band Suppressed Carrier Professor Z Ghassemlooy Electronics and IT Division School of Engineering Sheffield Hallam University U.K.

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2 Content Theory Transmitter Implementation Detector Implementation Power Analysis Summary

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3 Single Side Band Suppressed Carrier From DSB-SC spectrum: Information m is carried twice Bandwidth is is high c - m c c + m Carrier USB LSB Single frequency Question: Why transmit both side bands? Ans: Question: Can one suppress one of the side bandcarrier? Ans.: Yes, just transmit one side band (i.e SSB-SC) System complexity at the receiver But what is the penalty?

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4 SSB-SC - Implementation Frequency discrimination Multiplier Message m(t) Local oscillator c(t) = cos c t Local oscillator c(t) = cos c t DSB-SC Band pass filter c + c Band pass filter c + c Band pass filter c - c Band pass filter c - c Upper sideband Lower sideband

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5 SSB-SC - Waveforms B = 2 m USB Bandwidth B = m B = m

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6 SSB-SC - Implementation cont. Phase discrimination (Hartley modulator) X X SSB-SC signal X X E m sin m t sin c t sin c t cos c t Carrier 90 o phase shift 90 o phase shift Message m(t) 90 o phase shift 90 o phase shift + - E m cos m t cos c t E m sin m t E m cos m t v(t) =E m cos m t cos c t + E m sin m t sin c t = E m cos ( m - c )t LSB v(t) =E m cos m t cos c t + E m sin m t sin c t = E m cos ( m - c )t LSB v(t) =E m cos m t cos c t - E m sin m t sin c t = E m cos ( m + c )t USB v(t) =E m cos m t cos c t - E m sin m t sin c t = E m cos ( m + c )t USB

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7 SSB-SC - Hartley Modulator Advantages: –No need for bulky and expensive band pass filters –Easy to switch from a LSB to an USB SSB output Disadvantage: – Requires Hilbert transform of the message signal. Hilbert transform changes the phase of each +ve frequency component by exactly - 90 o.

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8 SSB-SC - Detection Synchronous detection Multiplier Low pass filter Low pass filter Message signal SSB-SC Local oscillator c(t) = cos c t Local oscillator c(t) = cos c t Condition: Local oscillator has the same frequency and phase as that of the carrier signal at the transmitter. mm 2c+m2c+m Low pass filter high frequency information

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9 SSB-SC - Synch. Detection cont. Case 1 - Phase error Multiplier Low pass filter Low pass filter Message signal SSB-SC Local oscillator c(t) = cos ( c t+ ) Local oscillator c(t) = cos ( c t+ ) Condition: Local oscillator has the same frequency but different phase as that of the carrier signal at the transmitter. mm 2c+m2c+m Low pass filter high frequency information

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10 SSB-SC - Synch. Detection cont. Case 1 - Frequency error Multiplier Low pass filter Low pass filter Message signal SSB-SC Local oscillator c(t) = cos ( c + )t Condition: Local oscillator has the same phase but different frequency as that of the carrier signal at the transmitter. m + 2 c + m + Low pass filter high frequency information

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11 SSB-SC - Power The total power (or average power): The maximum and peak envelop power

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12 SSB-SC - Summary Advantages: –Lower power consumption –Better management of the frequency spectrum –Less prone to selective fading –Lower noise Disadvantage: - Complex detection Applications: - Two way radio communications - Frequency division multiplexing - Up conversion in numerous telecommunication systems

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