Abstract: A radio link for a digital radio transmission system having spatial and/or angular diversity is optimized in real time by searching for a minimum of the analog BER function BERn(.phi.), by analyzing the minimum to determine if it is an "absolute" minimum that will result in an optimal radio link, and if not, searching for another minimum until the absolute minimum is located. Once the relative phase .phi. corresponding to the absolute minimum has been thus determined with both channels having the same nominal attenuation level, the relative attenuation level T of the two channels may then be varied in order to optimize the dispersion Ban.sub.n (T) of the recombined data spectrum while holding the relative phase at its previously optimized value.

Abstract: A radio link for a digital radio transmission system having spatial and/or angular diversity is optimized in real time by first varying the relative phase .phi. between the two channels to locate an absolute minimum of the analog bit error rate function BER.sub.n (.phi.) with both channels having the same nominal attenuation level, and then by unbalancing the relative attenuation level T of the two channels in order to optimize the dispersion Ban.sub.n (T) of the recombined data spectrum while holding the relative phase at its previously optimized value.

Abstract: A system for detecting data spectrum distortion in a transmitted signal, in particular distortion caused by selective fading. The system includes: two blocks in parallel, which act on the spectrum average power of the input signal in an equal but opposite manner (i.e. they have equal slopes but act with opposite effect on the amplitude of the input signal versus frequency); two detectors which detect the average power output from the two respective blocks, each being associated with one of the blocks; and one comparitor for comparing the outputs of the two detectors. The system allows one to detect the asymmetries of the data spectrum and, by adding an AGC and a reference voltage, information related to the notch frequency f.sub.o is also obtained. The distortion measurement obtained in this manner allows one to generate a switching criterion, as a countermeasure for selective fadings in the transmitted signal.

Abstract: The invention relates to a system for initializing transmitters in high capacity digital radio links, in which a digital signal with QAM (Quadrature Amplitude Modulation) modulation is transmitted over a radio frequency carrier wave. The initialization of the transmitter is accomplished by generating a plurality of sinusoidal signals (tones), adding those tones together to simulate a digital singal to be transmitted, sending the simulated digital signal through the transmitter, and adjusting the transmitter to compensate for the intermodulation odd order products developed as a result of the nonlinearity of the power amplifier in the transmitter.