Sep 29, 2005CS477: Analog and Digital Communications1 AM Modulators, SSB Analog and Digital Communications Autumn

Sep 29, 2005CS477: Analog and Digital Communications2 AM – Power Calculations Lets calculate power in carrier and sidebands: (in one sideband)

Sep 29, 2005CS477: Analog and Digital Communications3 AM – Power Calculations At least 50% power is wasted in carrier

Sep 29, 2005CS477: Analog and Digital Communications4 DSB-SC or Simple DSB USB LSB

Sep 29, 2005CS477: Analog and Digital Communications5 DSB – Power Calculations (Criteria for good modulation!) How does AM compare with DSB? ( is power in one sideband)

Sep 29, 2005CS477: Analog and Digital Communications6 Power Calculations For DSB-SC or DSB: For DSB+C or AM: (100% modulation)

Sep 29, 2005CS477: Analog and Digital Communications7 Tone Modulation Information signal is For DSB-SC or DSB: For DSB+C or AM:

Sep 29, 2005CS477: Analog and Digital Communications8 Tone Modulation For DSB-SC or DSB: For DSB+C or AM:

Sep 29, 2005CS477: Analog and Digital Communications9 Modulators Product modulators Require analog multipliers Variable trans-conductance multipliers Hall effect devices Hard to build Generally limited by low power and low frequencies Modulators based on filtering undesired frequencies Square-law and balanced modulators Ring modulator Switching modulator Avoid heavy filtering by not generating higher frequencies

Sep 29, 2005CS477: Analog and Digital Communications10 SSB-AM USB LSB First consider DSB-SC Pass it through an “SSB filter” Islands are not symmetric around

Sep 29, 2005CS477: Analog and Digital Communications11 SSB and DSB Comparison For DSB: For SSB: (Transmission BW is twice the signal BW)

Sep 29, 2005CS477: Analog and Digital Communications12 Tone Modulation: SSB & DSB Information signal is For DSB-SC or DSB: For USSB: For LSSB: