System to generate switching criteria and equalize adaptively in data spectrum

摘要

The system according to the invention for detecting data spectrum distortion in transmission, in particular the distortion caused by selective fading, is based on identifying in-band dispersion, i.e an amplitude distortion and for this aim it substantially includes: two blocks in parallel, the module behaviour of which have equal slopes but different signs upon a change of frequencies; two detectors of average power, each being associated to one of said blocks; and only one detected average power comparison means. This system allows to detect the assymmetries of the data spectrum and by adding an AGC and a reference voltage, also the information related to the central notch is obtained. The distortion measurement obtained in this manner allows to generate a switching criterion or control, as countermeasure for selective fadings. The criterion is obtained at intermediate frequency and generates an alarm whenever the distortions caused by fading evolve towards an error condition for the type of modulator-demodulator that is used. With reference to the "signature" drawn for a BER equal to 10<-><6> a curve (IF signature) is drawn representing the activation of an alarm whenever fading parameters exceed prefixed values. The IF signature is much more extended in frequency than the BER = 10<-><6> signature. Adaptive equalization is carried out at intermediate frequency on amplitude only, leaving group delay distortions unaltered.