Abstract: A feedback circuit for controlling the phase of a local oscillator provided with frequency adjusting means and delivering a local carrier wave for demodulating a data signal transmitted by single side band amplitude modulation, the said feedback circuit comprising at least one sign multiplier (21) producing the product of the sign of the local demodulation carrier shifted by a phase difference of .pi./4 multiplied by the sign of the data signal to be demodulated, followed by a sign coincidence auto-correlator (22) which controls the said frequency adjusting means and correlates two versions of the signal delivered by the sign multiplier (21), one of the two versions being delayed relative to the other by an odd multiple of one fourth of the period of the carrier used for the amplitude modulation on transmission.

Abstract: A digital sinewave generator can be used in digital equipment, e.g. instead of a local oscillator for modulation/demodulation of signals. If there is no simple relationship between sampling rate and the frequency of the sinewave, successive sample values must be calculated since storage of these values would be prohibitive. For a sinewave Re.sup.jk.phi. sampled at successive instants k=0, 1, 2, . . . etc. separated by a phase angle .phi., quadrature components A.sub.k +jB.sub.k =Re.sup.jk.phi. can be calculated using the algorithm:A.sub.k+1 =cos.phi.A.sub.k -sin.phi.B.sub.kB.sub.k+1 =sin.phi.A.sub.k +cos.phi.B.sub.k.Unfortunately it is impossible for cos.sup.2 .phi.+sin.sup.2 .phi. to be exactly equal to unity if calculations are performed with finite precision using an even number base, which as the effect of causing the modulus of a sinewave generated by this algorithm to tend exponentially to 0 to .infin.. The present invention overcomes this by using the above algorithm to obtain approximations A.sub.

Abstract: The present invention comes within the field of synchronous digital transmission. It relates to the recovering the carrier (which may be suppressed carrier) of an amplitude modulated synchronous digital signal. It provides a circuit which includes an oscillator (41) of adjustable frequency and phase to generate a local carrier, a demodulation circuit whose input(s) receives the local carrier (possibly phase shifted by .+-..PSI. (42,44,46,47) and the amplitude modulated synchronous digital signal e(t) and control means (48,49) which control the phase and the frequency of the oscillator from the signals delivered by the demodulation circuit and which comprise at least one sign coincidence autocorrelator. It advantageously applies to demodulating amplitude modulated single side band bipolar coded synchronous digital signals.

Abstract: The present invention comes within the field of synchronous digital transmission. It provides an automatic variable equalization network (1) equipped with phase-locking means, in which a sign coincidence autocorrelator (30) correlates the polarities of two versions of the equalized signal delayed in relation to each other by .tau., an integer multiple of the unit time interval of the transmission. It is used advantageously for equalizing synchronous digital transmission channels in switched telephone or telegraph networks.

Abstract: A magnetic recording disc includes a plurality of sectors, each of which includes a plurality of data tracks and a reference zone containing information for identifying the data tracks. Some of the sectors are standby sectors containing information which would normally be contained in the sectors containing the data tracks. The reference zones of all sectors contain binary fault indicating bits which indicate whether a particular sector contains faults, and parity bits having values dependent on the location of the parity bit and the value of the fault bit at the same location as the parity bit. A data processor commands a read out head for the disc to be located at a particular position. From the command position of the data processor and the value of the fault bit, the data processor computes an expected parity bit value. The expected parity bit value is compared with the parity bit value read from the disc to provide an indication as to whether the fault bit is accurate.

Abstract: This system is provided for the field of electronic facsimile transmitting of a picture and relates more particularly to the compression of data to reduce the number of bits to be transmitted at a given resolution of the picture. Compression is effected by a correlation of neighbouring points of the picture by omitting, at the transmitting end, one point in four on two adjacent lines and by restituting it at the receiving end by means of a relatively simple Boolean function which takes into account the structure of the characters used in that picture. That first compression may be combined with a second compression due to the coding of the length of a white range.