Abstract: A microwave oscillator has a cavity which is excited with an active element. The phase noise characteristic of the oscillator is improved in that a frequency discriminator utilizes the same oscillator cavity. The waves transmitted and reflected by the cavity are measured, combined and detected by a pair of low noise diodes. The signals obtained are compared to produce a control signal for a phase shifter which is connected between the active element and the cavity. The cavity is preferably a dielectric resonator.

Abstract: A procedure and device are described for cancellation of the echo produced in telephone connections with electrical time-variant characteristics such as for example those affected by phase roll. The echo canceller obtained in accordance with the procedure which is the object of this invention produces an estimate of the echo signal by means of appropriate digital filtering of the signal originated by the far-end talker. The estimated echo is then subtracted from the actual echo. Filtering is activated by an IIR digital filter whose adaptive coefficients are updated by use of an adaptive algorithm based on decimation of the square error. The high convergence speed of said algorithm in the calculation of the coefficient correction step allows a correct estimate of the echo even in case of connections affected by phase roll.

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 timing recovery circuit of the sampling type uses two signal samples per symbol time and utilizes a control signal (for a local oscillator which generates the timing signal) which is given essentially by the product of a reconstruction error signal, derived at the generic sampling instant, multiplied by the difference between the values of the reconstruction symbols, taken at one-half symbol interval respectively before and after said sampling instant. The derived control signal allows generation of a timing signal which positions with extreme accuracy and stability the sampling instant of the received signal at the minimum points of the mean square error curve, even under selective fading conditions.

Abstract: A comb-line band-pass filter with circular cross section is made up of internal rods constituting the resonators of the filter and brought to resonance by the use of tuning screws and alternating with coupling screws. In the filter the rods are inserted in such a manner that each one is rotated in relation to the preceding one by an angle of 0.degree.<.alpha.<90.degree. while the coupling screws are placed at an intermediate angle. For equal electrical characteristics the length of the filter is also a function of the rotation angle of the rods.

Abstract: The structure includes a conductive path and a ground plane applied to opposite faces of an insulating support. The ground plane has parallel slots placed under the conductive path and transversely thereto.