Abstract: Complex coding of speech signals, as this is used, for example, in the GSM half rate speech coder, requires the use of a signal processor. On the other hand, a hands-free facility requires an arithmetic unit which adaptively calculates filter coefficients. This is only effected during speech pauses in which the speech coder is switched to a mode in which it generates codes for background noise with only little processing circuitry and expense. According to the invention, the signal processor for the coding device is therefore used for calculating the coefficients for the echo cancelling filter during speech pauses. This requires the use of not more than a single signal processor which can thus be used twice.

Abstract: A method of manufacturing a scandate dispenser cathode having a matrix (1) at least the top layer of which consists substantially of a mixture of tungsten with scandium oxide or with a mixed oxide comprising scandium oxide. When sintering of the matrix is carried out at a temperature between 1300.degree. and 1700.degree. C., preferably at approximately 1500.degree. C. and in a hydrogen atmosphere, cathodes are obtained having a better recovery after ion bombardment compared with cathodes sintered at 1900.degree. C. Sintering in hydrogen results in a better reproducibility.

Abstract: A high-frequency modulator which is linearly modulated in a frequency range around a center frequency and comprises a high-gain field effect transistor whose output is fed-back to the input from a coupler constituted by two relatively fine lines which are sufficiently remote from each other to provide that at the input of the transistor the majority of the high power available at its output is reinjected, and thus a high external Q factor is obtained. The modulation circuit which is arranged in parallel with the feedback network includes a varicap which is arranged in series with three line elements and a fixed capacitor calculated for optimizing the linearity of the frequency modulation as a function of the control voltage of the varicap. The circuit may be used for example, in equipment such as radio altimeter sources or proximity fuses, auto-directional systems and long-range radar.