Modulation Schemes

􀂄A single frequency signal, known as the Carrier, is selected to lie within acceptable range of frequencies.
􀂄Amplitude, Frequency or Phase is then varied, or keyed, in accordance with the data signal to be transmitted.
􀁺Amplitude shift keying(ASK or AM) is rarely used because of attenuation problems.
􀁺Frequency shift keying(FSK or FM), is used with lower bit rate modems. Relatively simple demodulation circuitry.
􀂄The Signalling Rateor Baud Rateis the number of times per second the amplitude, frequency or phase of the transmitted signal changes.