Abstract: Sonar apparatus provided with a beamforming network (1) containing several receiving channels (4A-M) for supplying, for each direction of beam incidence, digital composite signal products obtained by superposition of the receiving channel output signals and for transforming the signal products to a low-frequency band. The signal products are fed to a signal analysing circuit (3) comprising blocking circuits (62 and 63), and to a noise detector (61) for deriving, for each direction of beam incidence, a blocking circuit control voltage from the interference signal components in the signal products. The noise detector selects signals outside the low-frequency band part representing the transmitting/receiving band, and determines the modulus of the filtered signals and the average value thereof. The modulus and, after thresholding, the average value are fed to a comparator (77) to generate the control voltage.

Abstract: An arrangement for generating amplitude-modulated, ultrasonic transmission pulses comprising at least a switching circuit (4) provided with an inductive load (12) for generating the transmission pulses and controlled with a plurality of switching pulses per pulse interval; a memory (2) filled with information about the appropriate pulse width of the switching pulses as required per transmission pulse interval; and a switching-pulse generator (3) for producing switching pulses using the pulse width information and timing signals determining the switching pulse frequency. This arrangement is suitable for sonar applications for the purpose of improving the detection of doppler shifted echo signals.

Abstract: A radio direction finding apparatus comprising an omnidirectional receiving element (21), an array of directional receiving elements (1.1-1.2N), two log video detectors (15, 16) suited for separate connection to two contiguous elements of said array and a subtraction circuit (27) for generating a signal containing the azimuth data of an r.f. transmitter. In order to select echoes received through the main lobes of the two connected receiving elements from those received through the main lobe of the one element and a side lobe of the other element, the radio direction finding apparatus is provided with a threshold circuit (18) and two gate circuits (19, 20) separately inserted between the log video detectors (15, 16) and the subtraction circuit (27). The threshold circuit (18) passes the applied signals through the gate circuits (19, 20) if the strength of the latter signals exceeds that of the echo signal obtained from the omnidirectional receiving element (21) via a third log video detector (22).

Abstract: Passive frequency measuring circuit comprising a number of frequency discriminators to obtain a digital code representing the frequency of an applied r.f. signal. Each discriminator is tuned to different frequency ranges, and provided with a plurality of similar frequency analysers for the phase detection of the applied r.f. signal passed through different delay lines. As each discriminator delivers an ambiguous code at the boundaries of its characteristic, a digital filter is incorporated to resolve the ambiguity. If such an ambiguity is established, an adjoining discriminator is activated to deliver information for obtaining a digital code representing an unambiguous frequency value.