Modulation and its Need

MODULATION:

✓ Modulation is the process of superimposing low-frequency information signal on a high frequency carrier signal
✓ In modulation process Some parameter of carrier wave (such as amplitude, frequency or phase is varied in accordance with modulating signal.

NEED OF MODULATION:

1) Reduction in height of antenna
2) Avoid Mixing of signals
3) Increases the range of communication
4) Multiplexing is possible
5) Improves quality of Reception

1) Reduction in height of antenna:
> For the transmission of radio signal, the antenna height must be multiple of (λ/4).
Here, λ is the wavelength λ= C/f where C is velocity of light and f is frequency of the signal to be tx.
> The minimum antenna height required to transmit a baseband signal of f-10KHz is
Calculated as follows Minimum antenna height =λ/4 = C/4f = 3x10^8/4x10x10^3 =7500 m i.e 7.5Km
The antenna of this height is practically impossible to install
> Consider a modulated signal at f = 1MHz The minimum antenna height is given by,
Minimum antenna height =λ/4 = C/4f = 3XI0^8/ 4x10x10^6=75m
> This antenne can be easily installed practically Thus, modulation reduces antenna height
2) Avoid Mixing of signals:
> If the baseband sound signal are tx without using the modulation by more than I tx, then all the signal will be in same frequency range i.e 0-20KHz.
> Therefore all signal get mixed together and a Rx cannot separate them from each other.
> So if each baseband sound signal is used to modulate a different carrier then they will occupy different slots in frequency domain. Thus modulation avoids mixing of signa.
3) Increases the range of communication:
> The frequency of baseband Signal is low and the low frequency signal cannot travel a long distance when they are Tx. They get heavily attenuated.
> The attenuation reduces with increase in frequency of the Tx signal and they travel longer distance.
> The modulation process increases the frequency of signal to be Tx. Hence increases the range of communication.
4) Multiplexing is possible:
> Multiplexing is a process in which 2 or more signal are Tx over same communication channel Simultaneously. It is possible only with modulation. The multiplexing allows the same channel to be used by many signals.
> So many TV channels use same frequency range, without getting mixed with each other or different frequency signals can be Tx at same time.
5) Improves quality of Reception:
> With frequency modulation (FM) and digital communication techniques like PCM, the effect of noise is reduced to a great extent. This improves quality of reception.

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