Constellation diagram

June 1, 2012.

The constellation diagram is a graphic representation (called I-Q) of the digital symbols received over a period of time.

There are different types of constellation diagrams for the different modulation modes. With the RANGERNeo + it is possible to display constellations for DVB-T/T2, DVB-C/C2, and DVB-S/S2 (according to model).

DVB-T2 constellation diagram for RANGER Neo + field strength meter
DVB-T2 constellation diagram for RANGERNeo +

In case of an ideal transmission channel, free of noise and interferences, all symbols are recognised by the demodulator without mistakes. In this case, they are represented in the constellation diagram as well defined points hitting in the same area and forming a clear dot.

Noise and impairments cause the demodulator to not always read the symbols correctly. In this case the hits disperse and create different shapes that at the end will allow to determine at a glance the type of noise in the signal.

Every modulation type is represented differently. A DVB-C 16QAM signal is represented on the screen by a total of 16 different zones, and a DVB-C 64QAM is represented on the screen by a total of 64 different zones and so on.

The constellation shows in different colours the density of hits and includes zooming and scrolling possibilities and also a clear button to clean the picture.

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PROMAX is a leading manufacturer of test and measurement systems, broadcast and TV signal distribution equipment. Our product lines include measuring instruments for cable TV, satellite TV, broadcast, wireless and fibre optics networks, FTTH and GPON analyzers. DVB-T modulators, IP streamers or IP converters (ASI, DVB-T) are among the company’s latest developments.