Fresnel plan   (representation of a modulated signal as a vector)

This graph shows the path of a 4PSK / 140 Mbit/s modulated signal at the output of a transmission channel. As the channel is intersymbol-free, the signal crosses a 0.707 j 0.707 point at every symbol. The roll-off has been chosen very small (R = 0.2, very sharp filter edges) to increase overshoots.

This graph can be used as a tutorial illustration of digital modulations, showing the large variations of the signal envelope.

fresnel.gif (17093 octets)

This graph is displayed by the third module of the following canal :

canal1.gif (7496 octets)

A very simple canal (only three modules)

The three following figures display the parameters of each module :

modulator.gif (12084 octets)

Parameters of the first module ("NO"  in the third line means standard PSK.)


Roll-off.gif (9361 octets)

Parameters of the second module (a unique filter with 100% percentage of the total roll-off gives the same result as two cascaded filters with 50% percentage)


Graphics.gif (10201 octets)

Parameters of the third module


Other examples : Eye diagram         Group delay of a feeder          Group delay of a filter       Interferences  Bit Error Rate    Multicarrier amplification     Constellation   Differential gain