Abstract: There is described a stabilization process for the local oscillator frequency in wide-band tunable DROs employed in receivers of a digital microwave radio link. A microprocessor, already provided for normal operation control, cyclically reads the control voltage of a VCO inserted in PLL which reconstructs an intermediate frequency carrier used to coherently demodulate the received signal. The voltage read is compared with an optimal reference value by taking an error signal which controls a varicap diode of the DRO for tuning correction. With each reading, the optimal value can be modified on the basis of temperature data supplied by a heat sensor to cancel the effect of temperature on the reference.

Abstract: A process for actuation of multi-level digital modulation, and in particular QAM modulation, by using a single microprocessor is described. The process calls for synchronism of all the frequencies in play. The symbols of the "in phase" and "in quadrature" channels and are oversampled and appropriately digitally filtered. A digital carrier is QAM modulated simply by selecting in string the symbols belonging to the digitally filtered channels taken with their true or negated value. These symbols are then sent to a digital/analog converter followed by a reconstruction filter to obtain the corresponding QAM modulated analog carrier.

Abstract: A circuit and method for the acquisition of carrier synchronism in coherent demodulators which operate with carriers modulated by Phase-Shift Keying (PSK). The invention makes use of simple, low-cost circuitry and gives the phase-lock loop of the demodulator an added frequency characteristic which prevents false locks and ensures lock between the local carrier and the reference signal even for very large frequency variations.