Modulation scheme
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The modulator converts an input signal into a form suitable for RF transmission. The demodulator recovers the original signal. Since the RF signal is a based sine wave oscillating around the transmission frequency, the modulator has to modulate this sine wave in a way so that all information is transmitted and well-recoverable but only as little bandwidth as allowed is allocated.
The more the modulation scheme modifies the original sine wave the more the frequency of the RF sine wave will vary -- the higher the bandwidth will be.
| Shortform | Name |
|---|---|
| AM | Amplitude Modulation |
| FM | Frequency Modulation |
| PM | Phase Modulation |
| Shortform | Name |
|---|---|
| ASK | Amplitude Shift Keying |
| FSK | Frequency Shift Keying |
| BPSK | Binary Phase Shift Keying |
| QPSK | Quadrature Phase Shift Keying |
| QAM-16 | 16-state Quadrature Amplitude Modulation |
| QAM-32 | 32-state Quadrature Amplitude Modulation |
| QAM-64 | 64-state Quadrature Amplitude Modulation |
| QAM-128 | 128-state Quadrature Amplitude Modulation |
| QAM-256 | 256-state Quadrature Amplitude Modulation |
| 8VSB | 8-state Vestigial Side Band Modulation |
| OFDM DMT |
Orthogonal frequency division modulation Discrete multitone modulation |
If you interested in the inner workings and the theory behind demodulators for digital TV, there are some signal processing tutorials at http://www.complextoreal.com/.