Abstract: The disclosure relates to the changing of frequencies. The mixing of a signal at a frequency Fe and of the signal of a local oscillator gives a resultant signal that comprises a first component at the useful frequency, a second component at the frequency of the oscillator and a third component which is an image of the first component with respect to the second one. A filtering highly attenuates the third component. A servo-control makes a part of the signal from the oscillator undergo variations in amplitude and phase before adding it to the resultant signal to be filtered; the variations are made so as to obtain a minimum energy from the second component before filtering. Application to the changing of frequencies with suppression of the component at the frequency of the local oscillator.

Abstract: The disclosure relates to the linear power amplification, in a single channel, of a composite signal formed by two independent signals. In a single channel formed by correction means followed by a linear preamplifier followed by a saturated amplifier, the filtering and symmetry effect produced, both in the correction means and in the saturated amplifier, is advantageously used to compensate for clipping of the composite signal due to the amplifier. This makes it possible to obtain an undistorted output signal whose amplitude exceeds the level of saturation of the saturated amplifier. The compensation makes it necessary for the transfer characteristic of the correction means to have a given slope between two points beyond which the saturation appears in the saturated amplifier and a slope that is substantially thrice the given slope on each side of these two points.

Abstract: A high-frequency wideband power amplifier, of the type comprising an amplifier stage with at least two transistors mounted as a differential stage, coupled at input and at output to a matching circuit further comprises, in order to convey each bias voltage to the amplifier stage, at least one high-frequency transmission line section with a length close to a quarter of the wavelength of the carrier of the signal to be amplified, the impedance of which, brought in parallel on each transistor, is negligible with respect to the high frequencies and the series impedance of which is negligible in the baseband of the signal to be amplified; the line sections conveying the bias voltages to the input of each transistor are identical to one another in length and in impedance, and the same is the case for the line sections conveying the bias voltages to the output of each transistor.

Abstract: The receiving antenna comprises at least two sectors or sections of paraboloids focusing the radiation onto their axes at points F.sub.1 and F.sub.2 respectively offset by a whole number of wavelengths of the received radiation. Each sector or section is associated with a helicoidal source located in its focal zone and having the same axis as that of the corresponding sector.

Abstract: A system intended for the simultaneous reception of several TV channels retransmitted by satellites. This system comprises a multi-frequency microwave frequency head, installed in an external unit, whose inputs are connected to the satellite antennas. Wide band demodulation is made possible by a microwave frequency source controlled by a synthesizer. Digital signals transmitted by a link cable ensure programming of the synthesizer and therefore of the selected TV channels. A remodulation in amplitude modulation is performed for supplying signals in the 40-860 MHz band, carried by an existing link cable for terrestrial antennas. The system finds particular application to the simultaneous reception of several TV channels.

Abstract: A method and apparatus for measuring and correcting nonlinearities in a transmission system which transmits a modulated wave having a maximum peak level N.sub.C and with a frequency band [F.sub.1, F.sub.2 ]. The system transmits a composite signal having a carrier frequency proximate to one end of the frequency band, modulated by a low frequency signal having a level varying between zero and the peak level N.sub.C. The composite signal also has two other signals with carrier frequencies proximate to the other end of the band and having frequencies differing by an intercarrier frequency. The composite transmitted signal is received and analyzed for the presence of a signal at the intercarrier frequency which varies in amplitude with the nonlinearity of the system. Linearity of the system is obtained when the signal at the intercarrier frequency is zero or less than a predetermined value.

Abstract: The disclosed antenna is designed notably for the emission of television and radio broadcast signals in the decimetrical wavebands. It comprises:a vertical, central supporting tube,a plurality of identical radiating networks evenly distributed around the central tube, each consisting of a vertical bifilary line symmetrically supplying, supporting and coupling a plurality of horizontal dipoles evenly distributed along this bifilary line, and,a system for the distribution of equiphase, equal power, identically and simultaneously supplying the radiating networks through a single coaxial supply line. The antenna has a reflector thus substantially reducing its weight and its windward surface as compared with standard antennas with panels generally used in this band. Advantageously, these antennas are superimposed and enclosed in a sealed radome which is substantially cylindrical and self-supporting and superimposable. This antenna gives an omnidirectional diagram with 0.

Abstract: Disclosed is an energy coupling device which can be used with metrical and decimetrical waves. To distribute, equipotentially and in equiphase, towards n users, the energy coming from m equipotential sources in equiphase, a 90-degree of 3 dB hybrid circuit is connected at the output of each source. This circuit distributes the power equally and with a 90-degree, aperiodic phase shift, towards two equipotential distributors in equiphase, with m inputs and n outputs, having one and the same input/output phase shift. The two distributors are connected, respectively, to the two ports of a pair of conjugated ports of n 90-degree 3 dB hybrid circuits. The powers recombined in these n circuits are respectively delivered to n users.

Abstract: The disclosure concerns automatic measuring stands. The automatic measurement of the amplitude of an intermodulation line at the output of a TV transmitter is difficult to achieve because this line is often drowned in a cloud of noise formed by the spectra of lines due to the numerous frequencies of the line frequency. The standard way to make the measurement is to do a visual interpretation. When the measurement is done automatically, this visual interpretation is not possible. The method according to the invention uses the a priori knowledge of the existence of a steady level at the peak of the line to be measured.

Abstract: A circuit for high speed control a field effect power transistors. This circuit has a transformer with a primary winding and a secondary winding. The secondary winding transmits control signals to gates of the field effect power transistors. An energy storage structure is coupled to the transformer, and stores energy required for controlling the gates of the field effect power transistors. This energy is stored during an inactive phase of the control signal. A transmission structure is coupled to the transformer, and is fed with energy stored in the energy storage structure. In this way, the transmission structure uses energy stored in the energy storage structure to supply the control signals to the gates of the field effect power transistors. Therefore, the secondary of the transformer is not loaded during this time. At other times, the transmission structure isolates the output of the transformer from the rest of the circuit.

Abstract: An automatic symmetry correction circuit is provided for a symmetrical current chopper. This structure includes two current channels controlled alternately by two signals of frequency f.A resonant LC circuit is tuned to the frequency f and energized by the currents passing through each of the two channels.A control circuit is coupled to the resonance circuit for adjusting the symmetry between the amplitudes of the currents flowing through each of the two channels as a function of the amplitude of the oscillations of frequency f generated by the resonance circuit.

Abstract: A device for the automatic precorrection of non-linearities of a power amplification chain in a common channel television transmitter. The device has a first circuit for detecting the component to be corrected prior to amplification and addition of the components to be simultaneously amplified, a circuit for selecting the same components after amplification in a common channel, an attenuator of the latter component having an attenuation coefficient equal to the linear part of the amplification chain gain, a second detection circuit, an analog divider receiving the two detected components, whereof the output is coupled to the precorrection control input of a precorrection circuit upstream of the first precorrection circuit.