Combining the low frequency signal with very high frequency radio wave is called

Concept:-

Modulation:-  It is the process of attaching a low-frequency base-band signal to the high-frequency carrier wave in order to get high frequency modulated signal for its effective transmission.

There are basically three kinds of modulations:-

1. Amplitude modulation (AM)

2. Frequency modulation (FM) and

3. Pulse modulation (PM)

There are three types of modulation based on which parameter is modified. These are

1) Amplitude modulation (AM): In this kind of modulation the amplitude of the carrier signal is modified according to the instantaneous amplitude of the base-band signal.

In AM the frequency and the phase of the carrier signal remain constant. 

Amplitude modulation is used in broadcasting (radio and TV).

2) Frequency modulation (FM): In this kind of modulation the frequency of the carrier signals is modified according to the instantaneous amplitude of the baseband signal in frequency modulation.

Here the phase and the amplitude of the carrier signal remain constant. 
An increase in the amplitude of the baseband signal increases the frequency of the carrier and vice-versa.

3) Phase Modulation (PM): If the instantaneous amplitude of the baseband signal modifies the phase of the carrier signal keeping the frequency and amplitude constant is called Phase modulation and this modulation is used to generate frequency-modulated signals.

It is similar to frequency modulation except that in this modulation the phase of the carrier is varied instead of varying frequency.