In amplitude modulation, the amplitude of the carrier signal is varied by the modulating signal. There are mainly three basic types of amplitude modulation schemes as described below:1. Double Sideband Full Carrier (DSB- LC)2. Double Sideband- Suppressed Carrier (DSB-SC)3. Single sideband- Suppressed Carrier (SSB-SC)Apart from these three, the other types of amplitude modulations are:4. Single sideband Full Carrier.
This could be used as compatible AM broadcasting system with DSB-FC receivers.5. Single Sideband - Reduced Carrier : Here an attenuated carrier is reinserted into the SSB signal, to facilatate receiver tuning and demodulation. This method is steadily replaced by SSB-SC.6. Independent Sideband Emission : Two independent sidebands, with a carrier that is most commonly suppressed or attenuated is used here. It is used in HF point-to -point radiotelephony, in which more than one channel is required.7. Vestigial Sideband : Here a vestige or trace of the unwanted sideband is transmitted, usually with the full carrier. This is used in video transmission.8.
Lincompex : This is an acronym that stands for 'linked compressor and expander'. it is used commercial HF radio telephony.The type of amplitude modulation used depends upon the application it is used for.Double Sideband full CarrierThis type of Amplitude modulation is also known as 'Full AM' or 'Standard AM'.Here the frequency sepectrum of th AM will have the carrier frequency, Upper sideband and the Lower Sideband. Therefore the DSB-LC signal may be written asv(t) = Vcsin`omega`ct + `(mVc)/(2)` cos (`omega`c - `omega`m)t - `(mVc)/(2)` cos(`omega`c + `omega`m)tThe bandwidth of the modulated wave is twice that of the information signal bandwidth.Double Sideband- Suppressed CarrierIn this type of amplitude modulation, both the sidebands namely Lower sideband and Upper sideband are present in the frequency spectrum but the carrier component is suppressed, hence the name Double Sideband suppressed Carrier.
The Carrier does not contain any information, so it is suppressed during modulation to obtain a better Power Efficiency.The DSB-SC signal may be written asv(t) = VUSB(t) + VLSB(t) = `(VmVc)/(2)` cos ( `omega`m + `omega`c ) t + `(VmVc)/(2)` cos (`omega`c - `omega`m) tBandwidth of the modulated wave is twice that of the information signal bandwidth.Single Sideband- Suppressed CarrierIn this type of amplitude modulation, the carrier is suppressed and it is either the Upper sideband (USB) or the Lower Sideband ( LSB) that gets transmitted. In DSC-SC the basic information is transmitted twice, once in each sideband. This is not required and so SSB-SC has an upper hand.The SSB-SC signal may be written asv(t) = VUSB(t) = `(VmVc)/(2)` cos ( `omega`m + `omega`c ) t 'OR'v(t) = LSB(t) = `(VmVc)/(2)` cos (`omega`c - `omega`m) tEither the Upper sideband or the Lower Sideband is transmitted. Here the bandwidth bandwidth is equal to the information signal bandwidth.