Modulation :- It is a process with which original SIGNAL is transmitted over a carrier wave with the fixed amplitude or frequency. Carrier wave is a signal, which is used for trans of audio or video. Mainly these signals are trans over telephone lines. Two basic operations are performed by the Modem :

1. Conversion of data from digital to analog form
2. Conversion of data from analog to digital form

Modulation is classified into :

1. Amplitude : In this technique, amplitude of the carrier wave is constant from SOURCE to destination to avoid attenuation of a signal. Amplitude is voltage between 2 consecutive peaks. It is peak-to-peak voltage.
2. Frequency : In this, frequency of the carrier wave is constant from source to destination in order to maintain speed of trans. It is no of cycles PER second. It is calculated in TERMS of wavelength (LAMDA). Wavelength is the distance between 2 consecutive peaks. Frequency & wavelength are inversely promotional to wavelength.
3. Phase modulation : In this technique amplitude as well as frequency of carrier wave is constant from source to destination. Phase Modulation is also called as Shift Key.

Modulation :- It is a process with which original signal is transmitted over a carrier wave with the fixed amplitude or frequency. Carrier wave is a signal, which is used for trans of audio or video. Mainly these signals are trans over telephone lines. Two basic operations are performed by the Modem :

Modulation is classified into :