In modulation we have the translation of frequency of the signal spectrum which allows it to adapt to the channel that it has to pass through.

Numerical modulation are those in which the modulating signal is numeric.

These modulations are used in data communication by modems, in radio bridges, in mobile telephones, in satellite connections.

There are essentially three kinds of numerical modulations:

• ASK
• FSK
• PSK

In ASK modulation, the digital signal, that is the information to be transmitted, modulates a sinusoidal carrier and varies its amplitude in such a way as to make it coincide with the logical one, the carrier itself, and the logical zero, the carrier absence, as shown in the picture.

This kind of modulation, is easy to carry out both in modulators and in  demodulators.
It has always been used in teleprinters and in some kinds of short distance radio bridge.

Unfortunately it is very sensitive to noise, for this reason nowadays it is less used than in the past.

In FSK modulation we have two possible carrier with different frequencies that are coupled to logical binary values 1 and 0 as in the picture.

This modulation pattern was used in the first modems, V21 and V23 which here very slow in comparison to the modern ones and it is today used in radio bridges and in GSM mobile telephone connections.

PSK modulation is certainly the most modern numerical modulation.

In this kind of modulation we have only one carrier so that two numerical values 1 and 0 are coupled to two different phases of the same frequency 0° and 180° respectively as in the picture. 

To increase data rate, maintaining constant modulation velocity, we transmit a great number of different angles, not only 0° and 180°. To have a simpler demodulation in reception, we vary signal amplitude too, because the modulation could be bad. This procedure is called QAM PSK modulation.

The most modern numerical modulations, which use a high big data rate, are amplitude and phase modulation.

This kind of modulation is used above all with modems, but also with radio bridges and satellite transmissions.

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• 16 QAM PSK MODULATION