Abstract: An apparatus and improved method for transmitting an information signal. According to the improved method, an information signal is transmitted under water from a transmitter located at a first place to a receiver located distant therefrom at a second place. In performing the signal transmission, a modulated ultrasound carrier signal is delivered to the water and is formed with a fixed amplitude value in the transmitter. The modulation is performed by pulse duration modulating (with an information signal) the ultrasound carrier signal which, in turn, has a given frequency. The modulated ultrasound carrier signal is then picked up from the water and is demodulated in the receiver in order to recover the information signal.

Abstract: A resonance oscillator comprises an active, e.g. disk-shaped, oscillator part (2) which is brought into contact, forming a couple oscillator, with a passive, comparatively longer oscillator part. This oscillator part, which basically determines the resonant frequency, consists of a variable-length solid column or liquid column (11) the length of which can be varied continuously in the direction of the sound vector in order to change the resonant frequency. The active oscillator part (2) is mounted on the base of an elongated resonance container (6) which contains the liquid that forms the liquid column (11). The length of the liquid column is varied by sliding a piston (5). The resonance container (6) is bounded by a corrosion-resistant, high-strength covering disk (7) of minimal thickness and is connected to an equalizing container (9) which receives the liquid displaced by the piston from the resonance container and returns the liquid to the resonance container.

Abstract: This invention relates to a method and system for verifying authenticity safe against forgery of an object releasing a function said object being of base material having random imperfections in or on the same, comprising measuring random imperfections in or on the base material of said object in a predetermined measuring track over the surface of said object of base material having random imperfections in or on the same by means of a detector for detecting said random imperfections, said random imperfections optionally being supplied to said base material, converting said measured random imperfections into pulses, supplying said pulses together with timing pulses to an AND gate, whereby only simultaneously arriving pulses are passed, supplying said passed pulses to a shift register shifting with said timing pulses to obtain a binary code, comparing said binary code with a previously stored binary code of the same object, whereby the function is released if said binary codes are identical; as well as a system

Abstract: This hands-free telephone prevents acoustic feedback between its speaker and microphone by attenuating either the transmission or receive path under the control of a corresponding pair of counters (computers), each counter sensing the signal divided and digitized from its corresponding path. An increase in counted pulses indicates feedback and causes a counter to more quickly reach a predetermined counter state (count), to trigger attenuation (damping) before it can be reset (restored) to zero by the other counter.

Abstract: A hands-free telephone set has both transmit and receive channels open for the reception of signals, while still inhibiting feedback-singing. Two switched attenuators are provided in cascade in each channel. The first attenuator is switched after a syllable delay, and the second attenuator is switched after a yet longer delay.

Abstract: A method of manufacturing documents such as paper money, credit cards, identification cards and the like in a manner so as to prevent forgeries thereof, comprises the steps of producing a base material, coating fibers with a magnetic or magnetizable material, and embedding the fibers into the base material during the production of the base material; an apparatus for checking the authenticity of documents such as paper money, credit cards, identification cards, and the like comprises in combination a document having fibers which are coated with a magnetic or magnetizable material embedded therein, detecting means for scanning the document to determine the number of magnetic particles present in the document, and means for moving the document and the detecting means relative to each other so as to provide a scanning trace, the document and the detecting means being disposed in a close relationship to each other.