Abstract: The invention relates to a method for frequency-shifting the modulus of the transfer function of a transversal filter.In a transversal filter having three delay lines Z1, Z2 and Z3 in series and four multipliers M'0 to M'3, the multiplier coefficients K0 to K3 of which are intended to eliminate the signals at frequencies in the vicinity of zero frequency and integral multiples of the repetition frequency Fr of the samples X.sub.i, the method consists in replacing the multiplier coefficients K0 to K3 by coefficients K'0 to K'3 which are deduced from the first by multiplying them by fixed coefficientse.sup.3jr, e.sup.2jr, e.sup.jr and 1 with r=2.pi.Fd/Fr.The invention is applicable in particular to the elimination of certain undesirable echoes from radar signals.

Abstract: The invention resides in the fact that the moving-clutter elimination filter is composed of several transversal filters whose n+1 multiplying coefficients K0, K1, . . . , K.alpha., . . . , Kn are fixed and are derived from the coefficients A0, A1, . . . , A.alpha., . . . , An of the fixed-clutter elimination filter by multiplying the latter by the factors:F.alpha.=e.sup.j2.pi.Fd.times.Tr(n-.alpha.).

Abstract: A receiver for a pulsed Doppler radar system comprising, connected in series, the following elements: an IF amplifier whose band width is equal to n times the spectral width of the transmitted pulses, a coherent IF detector, an A/D coder which operates at a sampling frequency at least equal to the passband of the IF amplifier and a digital filter whose pulse response is matched to the shape of the transmitted pulses. In a variant, the receiver comprises two signal channels I and Q.

Abstract: The device for processing logarithmic signals is intended to deliver the logarithm of the sum of the signals which are given under the logarithm sign. The digital processing device receives at least two logarithmic signals and comprises a subtracting circuit for forming the difference between the logarithmic signals applied to the inputs and a transcoder circuit for performing the operation ##EQU1## where Log r1 and Log r2 are respectively the signals applied to the inputs of the device and an adding circuit for performing the operation ##EQU2## and delivering the desired signal Log (r1+r2).

Abstract: One or more digital filters in the output of an echo detector in a radar or sonar system are periodically checked for correct operation by the application of a test signal to their input and the comparison of a resulting output signal with a predetermined response code stored in a read-only memory. If the comparison fails, a visual indicator is actuated; if the defective filter is one of a plurality, it is blocked and the gain of the echo detector is adjusted to compensate for the reduction in signal level. With two filters in respective circuit branches carrying detected echo signals in relative quadrature, these filters are tested alternately; failure of either of them may cause its automatic replacement by a standby filter.

Abstract: A receiver of a pulse-type radar has a main i-f channel feeding a fixed-echo suppressor of limited dynamic range and, in parallel therewith, an ancillary channel of extended dynamic range including a logarithmic amplifier and a processor. The latter averages the amplitude of incoming echo signals over a range-and-azimuth cell and then over one or more antenna revolutions. The resulting mean value of the signal amplitude is used to control the gain of a linear amplifier in the main channel so as to adapt the dynamic range of the echo signals to that which can be handled by the fixed-echo suppressor.