Abstract: A method of charging/recharging a secondary cell (24) by rectifying transmitted microwave energy which may be supplied by an unmodified microwave oven (18) into which oit is placed. The secondary cell (24) or an article, suchas a portable transceiver (10), containing a secondary cell is protected from harmful effects of microwave energy using a Faraday cage (12) and an antenna (16) disposed outside the Faraday cage picks up the energy which is rectified using s Schottky barrier diode (26). Optionally, the secondary cell may be disposed outside the oven (18) and the rectified current is supplied from the interior of the oven by way of conductors and/or a suitable connector.

Abstract: A communications device comprises a loop antenna having a plurality of feed terminals defining at least two terminal pairs. A controller is provided for selecting one terminal pair to enable reception or transmission from the loop antenna using the selected terminal pair. The selection of terminal pair is made based on the measurement of at least one parameter which is responsive to the proximity to the antenna of, for example, a user of the device. One terminal pair provides an antenna having matched impedance when the user is near the device, and the other terminal pair provides an antenna having matched impedance when the user is distant.

Abstract: A DC to DC power converter which can suitably be used, for example, in a charger device for rechargeable batteries has an input and a load output, a resonant transformer provided with a transformer input and a transducer output coupled to the load output, an output rectifier circuit coupled to the load output, a controllable transformer control circuit, in the form of a pulse providing circuit, coupled between the input of the converter and the transformer input, and a synchronous output rectifier circuit coupled between the transformer output and the load output. The transformer control circuit receives a control signal derived from a signal constituting or proportional a signal at the transformer output. The output rectifier circuit shows a variety of possible embodiments, each embodiment including at least two transistor switches which are connected between a different end of the transformer output and a same end of the load output.

Abstract: In a transmission system for transmitting speech and music signals, an input signal is coded in a coder (11) by a time domain coder (4). The output signal of the time domain coder (4) is decoded by a time domain decoder (8) and the signal thus decoded is subtracted from the input signal by a subtracter circuit (10). To improve the coding quality, the difference signal is coded by a frequency domain coder (12) and the output signal of the time domain coder (4) and the frequency domain coder (12) are combined in a multiplexer (14) and transmitted to a receiver.

Abstract: In a signal converter which derives from an input signal having a sample rate R/q an output signal having a larger sample rate R, the input signal is combined with a feedback signal in a subtracter to form a single combined signal. Samples of the combined signal are mapped into a larger number of output samples by a mapper forming part of a mapping arrangement which also produces the feedback signal. The formation of a single combined signal makes the signal converter less complex in design than it would be if a number of combined signals were formed. In a further embodiment a noise shaping filter is interposed between the subtracter and the mapper.

Abstract: In a transmission system a pair of signalling tone signals is transmitted by a transmitter (2) to a receiver (6) via a transmission channel (4). In the terminal (6) a tone detector is used to detect the presence of the pair of signalling tone signals. In order to improve the reliability of the tone detector in the case of differing strength of both tone signals, the decision on the presence of the pair of signalling tone signals is based on a combined strength measure which is determined by an adder (23). The combined strength measure is compared with a reference level TH.sub.2. In a further embodiment, also a check on the level of the individual tone signals is done with comparators (11) and (9), in order to specify the maximum strength difference tolerated.

Abstract: A circuit arrangement for supplying a controlled substantially constant level of electrical power to a discharge lamp in a load circuit includes a feedback loop responsive to a comparison or difference between a power measure signal corresponding to electrical power consumed by the lamp and a reference signal corresponding to a desired consumed power. The power measure signal is formed by a power measure signal forming circuit which includes a one quadrant multiplier which receives at a pair of inputs respective lamp voltage and lamp current measure signals output from a sample and hold device arranged for sampling both a signal indicative of instantaneous lamp voltage and a signal indicative of instantaneous lamp current. The sampling is done at instants at which a signal which is indicative of the derivative of the lamp voltage passes through zero in a predetermined direction.

Abstract: A transmission system contains a speech coder which utilizes a pitch detector that is arranged to select a characteristic auxiliary signal portion from the signal to be coded in order to improve the quality of the pitch detection. The pitch is found by searching in the speech signal for signal portions that correspond to the characteristics auxiliary signal portion and by calculating the time difference between the respective signal portions.

Abstract: A circuit arrangement (16) for producing a D.C. current, includes a feedback loop for producing a reference current from an output terminal (27) with a negative temperature coefficient. The feedback loop includes a current-source stage (17, 18) which feeds a current mirror stage (19, 20, 21) in response to a measuring current supplied from a current bank (24, 25, 28, 29), which also produces the output reference current. The output of the current mirror stage (19, 20, 21) drives a working impedance formed by the main current path of a transistor 22, across which a control voltage is developed which is applied to a control input (23) of the current bank (24, 25, 28, 29). The circuit arrangement is advantageously combined with a reference current source (1) arranged as a bandgap circuit for producing a reference current on an output terminal (2) with a positive temperature coefficient, by enabling the user to select a current reference with either a positive or negative temperature coefficient.

Abstract: A receiver circuit, particularly an integrated, zero IF receiver circuit in which a direct conversion IF stage is separated from an antenna by a further fequency conversion stage which is AC coupled to the direct conversion IF stage. A single crystal oscillator generates a frequency which is multiplied prior to being applied as a local oscillator signal to the further frequency conversion stage and is used to produce another frequency, which is divided to block harmonics, prior to being applied as quadrature related local oscillator signals to the direct conversion IF stage. The direct coversion IF stage includes several dc nulling for compensating for dc offsets.

Abstract: In a microwave transmission system a microwave signal is transmitted by a transmitter (1) using an antenna (2) to a receiver (4) which employs an antenna (3). The received signal is coupled to a mixer (17) via a waveguide section (15) having a cut off frequency being higher than the frequency of the signal generated by the local oscillator unit (18). In this way undesired emission of local oscillator signal is avoided. Furthermore no additional image rejection filter is required.

Abstract: In a transmission system a signal is encoded in an encoder (7) and the encoded signal is transmitted by a transmitter (2) via a transmission medium (4) to a receiver (6). In the encoder, analysis parameters of the input signal are determined by an analyzer (8) and quantized by a quantizer (14). The transmitter transmits quantization level numbers to the receiver (6), and in the receiver decoded analysis parameters are derived by interpolating level numbers of two subsequent sets of analysis parameters, and subsequently determining the corresponding analysis. By interpolating the level numbers instead of the analysis parameters themselves, a substantial amount of computational complexity is saved.

Abstract: A portable communication device is described comprising a loop antenna. The loop antenna consists of a dielectric strip with overlapping conductive plates on both sides, so that capacitors are formed, which are arranged in series with one another. In order to have a good efficiency and at the same time a high insensitivity for detuning due to capacitive coupling of the antenna to the body of the user, the number of capacitors should be less than five an the capacitors should be arranged widely spaced over the loop.

Abstract: The Doppler angle is adjusted to a value close to the optimum Doppler angle DAopt, typically amounting to 60.degree., between the direction of an echographic excitation and the axis of a blood vessel in an echographic image, based on prior designation of an initial point in the vessel. The method includes a first measurement of the Doppler angle DA1 in a first, predetermined excitation direction, comparison of DA1 with Daopt, formation of .DELTA..theta.=.vertline.DAopt-DA1.vertline., and correction of the direction of the echographic excitation by the value .DELTA..theta. in order to shift it to a second direction.

Abstract: A radio receiver comprising signal receiving means(10), means(12) for adjusting the amplitude of a signal received by said signal receiving means, a signal transmission system(32) coupled to said means for adjusting the signal amplitude, an agc feedback loop(38,42,40) coupled between an output of the signal transmission system and a control input of the signal amplitude adjusting means, the agc feedback loop comprising means for producing a multiple switched agc signal.

Abstract: In a digital filter in which coefficients are realised using power of two weighting factors, it can occur that due to rounding errors the output signal shows some inaccuracies. By decomposing the filter coefficients into powers of two in such a way that most powers of two have a counterpart with an opposite sign, the rounding errors tend to cancel, resulting in a more accurate filter.

Abstract: In an MR method whereby artefacts can be eliminated in MR images of inclined slices which are situated outside the isocenter, the temporal variation of a phase error is calculated from the imposed (desired) variation of the magnetic gradient fields and the impulse responses of the gradient coil sub-systems generating these fields, and the measured MR signals are corrected accordingly.

Abstract: An electronic ballast for a fluorescent lamp includes a delay triggered circuit which, upon expiration of a predetermined period during which the lamp filaments, constituting opposite electrodes of the lamp, are preheated, applies high frequency operating voltage across the opposite electrodes of the lamp beginning with a transition from a condition of no voltage to a condition of full rated voltage which occurs within one cycle of the high frequency voltage. The sharp transition from zero "glow current" to full "arc current" at the end of the preheating period has been found to increase the life of lamps in the number of on-off starts, particularly with respect to lamps of poor quality. The rapid transition is possible because the ballast uses the same inverter and transformer for supplying preheating and operating voltages. The operating voltage is applied between the opposite electrodes of the lamp via an electronic bi-directional switch, controlled by a preheating delay RC timing circuit.