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: The antenna system for direct broadcasting satellite reception is formed by a parabolic reflector associated with source means, the reflector being positioned and held by means of a supporting foot formed by a hollow, tubular body fixed at its upper part to the rear central zone of the reflector and hinged at its lower part to a pedestal around a horizontal axis to define the elevation of the antenna. The pedestal includes a rotationally movable part to define the azimuth of the antenna. The tubular body of the pedestal supports a section sufficient to contain all the circuits associated with the antenna.

Abstract: The device for limiting the transmission power of radiowave transmitters comprises a limiting stage for attenuating the signal to be amplified before applying it to the input of the amplifying chain. A coupler collects part of the signal in order to apply it to the input of control means. A delay device is coupled between the coupler and the limiting stage and delays the signal to be amplifed before applying it to the input of the limiting stage. The control means block the limiting stage in order to prevent transmission of the signal to be amplified to the input of the amplifying chain when the level of the signal to be amplified overshoots a predetermined amplitude and hold the limiting stage in the blocked state after the level of the signal to be amplified has fallen back below the predetermined threshold during a sufficient period of time which is calculated so as to prevent any power overshoot.

Abstract: In equipment for transmitting or re-transmitting television signals comprising, in the intermediate frequency stage, group propagation time correction cells for linearizing the phase-frequency characteristic of the equipment, the non linearity correction system of the invention uses these cells while completing them with an amplitude pre-modulation control circuit and/or a frequency premodulation control circuit, for correcting amplitude and phase non linearities affecting the pole carrier frequencies of the correction cells.

Abstract: A selective efficiency (threshold) video frequency nonlinearity precorrection device comprising a direct channel (wide band channel) and an auxiliary processing channel (selected frequency correction channel), are both coupled to an input receiving the video frequency signal. The auxiliary channel may comprise a low pass filter, an inverting amplifier, a nonlinearity corrector circuit selecting a range of the signal limited by thresholds added with suitable phase and amplitude to the signal transmitted by the direct channel so that the resulting signal has, with respect to the input video frequency signal, compression or expansion limited to the range thus selected and only for the low frequency components of this signal.

Abstract: The present invention relates to a device for measuring in operation the non-linearity of equipment for the transmission of composite television signals. It comprises a processing circuit which samples an intermodulation product located outside the useful spectrum transmitted, but within the band of the equipment generating it, whose measurement is validated by a control circuit for predetermined instantaneous or average values of the vision carrier.

Abstract: A signal transmission system, particularly for television, comprising a nonlinearity precorrection device having a principal channel and a subsidiary channel. The subsidiary channel comprises a nonlinearity product generator with two amplification channels, a linear channel and a nonlinear channel which enable nonlinearity products having a suitable phase to be extracted by the difference of their output signals. The principal channel comprises a circuit formed from two linear channels in parallel whose output signals are added together in an adder. The output signals of the subsidiary channel and the principal channel are added. This precorrection device enables automatic correction of the nonlinearity products to be set up.

Abstract: A power amplification device for high-frequency amplitude-modulated signals comprises a first and a second amplifier employed respectively for amplification of a reduced-level HF modulated carrier signal and for amplification of the simple HF carrier signal extracted from the HF standard modulated signal and supplies in parallel the amplifier and a subtracter device through which the first amplifier receives the HF standard modulated signal. This results in excellent performances, high efficiency and stability, ease of maintenance and reliability.

Abstract: The transmission system essentially involves separate amplification followed by a combination under predetermined conditions of relative amplitude and phase, of a carrier signal modulated by the video-frequency information and having a reduced carrier level with the same unmodulated carrier, thus permitting a considerable improvement in both efficiency and reliability of conventional transmitters.