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Compare DSB-AM, DSB-SC and SSB

Short answer

DSB-AM is simplest (envelope detector) but least efficient (max 33.3% power, BW=2W). DSB-SC uses coherent detection, 100% power efficient, but still BW=2W. SSB is most complex yet most efficient: 100% power efficiency and only half bandwidth (W), saving power and spectrum.

Compare DSB-AM, DSB-SC and SSB in terms of complexity, power and bandwidth efficiency.

DSB-AM, DSB-SC and SSB are the three main forms of linear (amplitude) modulation. They trade circuit complexity against power and bandwidth efficiency.

Expressions (single tone Amcos⁡ωmtA_m\cos\omega_mt)

DSB-AM: Ac[1+μcos⁡ωmt]cos⁡ωctDSB-SC: AcAmcos⁡ωmtcos⁡ωctSSB: AcAm2cos⁡(ωc±ωm)t\begin{aligned} \text{DSB-AM: } & A_c[1 + \mu\cos\omega_mt]\cos\omega_ct \\ \text{DSB-SC: } & A_cA_m\cos\omega_mt\cos\omega_ct \\ \text{SSB: } & \frac{A_cA_m}{2}\cos(\omega_c \pm \omega_m)t \end{aligned}

Comparison

CriterionDSB-AM (FC)DSB-SCSSB
Transmitter complexitySimple (square-law, switching, high-level collector modulation)Moderate (balanced / ring modulator)High (sharp sideband filter or phase-shift network)
Receiver complexityVery simple envelope detectorCoherent detector + carrier recovery (Costas loop)Coherent detector, needs accurate frequency
CarrierTransmittedSuppressedSuppressed
Power for μ=1\mu=11.5Pc1.5P_c0.5Pc0.5P_c0.25Pc0.25P_c
Power efficiencyμ22+μ2\frac{\mu^2}{2+\mu^2}, max 33.3%100%100%
Bandwidth2W2W2W2WWW
Bandwidth efficiency50%50%100%
Noise performance (figure of merit)≤ 1/3 (with envelope detection)11
Typical useMW/SW broadcastingStereo FM, QAM, TV colourHF voice, telephony FDM

Remarks

  • Complexity: DSB-AM is the cheapest, which is why it is used for broadcasting where there are millions of receivers and one transmitter. SSB is the most complex; filter method needs very sharp filters and the phase-shift method needs an accurate 90∘90^\circ wideband shifter.
  • Power efficiency: DSB-AM wastes at least two-thirds of its power in the carrier. DSB-SC and SSB put all power into information-bearing sidebands. Compared with DSB-AM at μ=1\mu=1, DSB-SC saves 66.7% and SSB saves 83.3% power.
  • Bandwidth efficiency: SSB is best, using only WW; DSB-AM and DSB-SC both need 2W2W since both sidebands carry the same information.
  • Overall: DSB-AM = simple but inefficient; DSB-SC = power efficient but not bandwidth efficient; SSB = power and bandwidth efficient but complex. VSB is a compromise between DSB and SSB.

✓ Answer checked by Claude Opus 5.5 (high effort)

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