Electronique Marcel Dassault

Centre National Detudes Spatiales

Dassault Electronique

Dessault Electronique

Electronique Marcel Dassault & Centre National D'etudes Spatiales

Michel Geesen

Daniel P Ludwig

Jacques Mourant

Thierry Potier

Daniel Wozniak

Patrick Souty

A clock generates clock pulses defining a plurality of clock cycles. A circuit is connected to receive the clock pulses and measure a primary time of occurrence of an event with respect to a clock cycle. Logic circuits are provided to generate a timing pulse representing a time interval between the event and a clock pulse of the subsequent clock cycle. The timing pulse begins at the time of the event and ends on the occurrence of a subsequent clock pulse. A filter circuit receives the timing pulse and generates in response thereto a signal having an amplitude representing the duration of the timing pulse. The amplitude is measured to determine the width of the timing pulse thereby identifying the occurrence of the event with respect to a subsequently occurring clock pulse.

Apparatus and method for accurately measuring the time of an event

The invention concerns a feedback control loop comprising a mixer comprising a first input receiving an electromagnetic signal, and a second input receiving a first local signal; an intermediate frequency line mounted between the output of the mixer and the input of a phase comparator which receives on a second input a second local signal and has an output; and a feedback line connected between this output and the second input of the input mixer, and comprising a loop filter controlling a variable oscillator for providing the said first local signal as well as a second variable oscillator for providing the second local signal. The loop filter comprises (i) a proportional section mounted between the output and the control input of a second variable oscillator; (ii) an integral variable section mounted between the output of the proportional section and the control input of the first variable oscillator; and controller capable of progressively changing the parameters of the proportional and integral sections so as to progressively reduce the bandwidth of the phase control system and to increase the filtering of the noise and of the interference signals superposed on to the electromagnetic signal.

Receiver of an electromagnetic signal with a known nominal frequency,

The counter circuit is adapted to counting high frequency pulses and to being read while counting said pulses. It comprises a plurality of pulse counting stages of increasing numerical significance, and read means for reading the states of said stages. Said plurality of pulse counting stages comprises lower significance stages (10.sub.1 to 10.sub.4) connected as a synchronous counter (10) and higher significance stages (12.sub.1 to 12.sub.n) connected as a ripple counter (12). The synchronous counter is so connected that it counts the high frequency pulses (H) directly, and that any change of state required in any of its stages on counting a pulse occurs substantially simultaneously with the arrival of said pulse. The ripple counter is so connected that it counts count cycles of the synchronous counter, and that it takes a long time relative to the interval separating two successive high frequency pulses for a change of state to propagate, where necessary, from the least significant stage (12.sub.1) of the ripple counter to its most significant stage (12.sub.n). Early count signal means (24.sub.4) are provided to apply a count signal to the ripple counter during each count cycle of the synchronous counter at an instant which is early relative to the synchronous counter cycling from its full count to its empty count. Further, the read means (49) are provided with read timing means (24.sub.4 and 57) for causing the state of the ripple counter to be read regularly at a predetermined synchronous counter state.

Counter circuit for counting high frequency pulses using the combination

Apparatus for acquiring and processing incoming radio signals received from a plurality of stations, the frequencies of which are contained in a predetermined frequency band. The received signals are mixed with a local oscillator frequency which is repeatedly scanning the input frequency band at a fast rate produced from a frequency synthesizer whose control input is modified step by step to cycle through a corresponding predetermined set of programming values. The sweep rate of the programming value of the frequency synthesizer is so high that the stabilization time for the frequency at its output is significant with respect to the dwell time of the control signal of each programming value. The varying frequency signals at the output of the mixer are applied to the inputs of band pass filtering channels, to derive the frequency range of the incoming signals for frequency selective circuitry arranged to demodulate the received signals. The invention is useful to the processing messsages transmitted by beacons by a satellite receiver.

Apparatus and method for acquiring and processing radio signals received

An apparatus for acquiring and collecting messages aboard a satellite which are transmitted via respective radio-signals over different frequencies from a plurality of beacons comprises a receiver having an adjustable gain control input. An automatic gain control loop is provided for maintaining the gain of the receiver at a constant value. While the input frequencies of each input signals and time of arrival thereof are not exactly known, it is known that all these input frequencies are contained within a predetermined input frequency band which is periodically scanned by a frequency analyzer. This analyzer operates by scanning the center frequency of a band pass filter over the input frequency band and detecting the level of signals at the output of this filter for a plurality of successive frequencies within this input frequency band. The detected levels are digitized. The resulting digitized level indications are statistically analyzed and the result of this statistical analysis is used for adjusting the level of the gain control input of the receiver. According to an embodiment, only those detected levels which correspond substantially to input signals carrying messages retained for demodulation are used for determining an average level indication over a time period such as that for a full revolution of the satellite. The thus determined average level is compared with a reference value to adjust the receiver gain, thus eliminating gain variations due, for example, to aging of the components.

Apparatus for acquiring and collecting radio signals coming from a

An apparatus for receiving messages transmitted from a plurality of radio signal sources operating at different frequencies within a predetermined frequency band. Means are provided to frequency scan the receive signals, deriving information for determining the frequency range in which said signals lie. A demodulating phase locked loop is connected to receive the radio frequency signals, and an initial operating frequency for the phase locked loop is provided by the frequency range information determined from the means for frequency scanning. A resetting circuit is included to maintain the phase locked loop oscillator frequency at a value independent of the frequency of the radio signals.

Apparatus for collecting and processing messages transmitted at

The apparatus gives an indication of the location in time between two successive clock signals of an event to be timed. Such an event may be the arrival of a laser pulse at a satellite. An integrator circuit (C84) is charged by a relatively high charging current from a first current generator (66) during the period of time between the event and the next clock signal. The integrator circuit is then discharged by a smaller current of opposite sign from a second current generator (80). The ratio of the charge and discharge currents 'stretches' the inter clock pulse time interval to a length that can be measured by counting clock pulses as the integrator discharges. For this factor to be useful, it is essential that the charging current remains constant during charging and from one charging occasion to the next. This is achieved by keeping the generator (66) generating current constantly and by diverting the current through an integrator circuit by-pass (R78) when not integrating. Switching is done using two transistors (Q71 and Q72) that are as identical as possible, and independently controlled in phase opposition. The by-pass current is detected and used to regulate the generator (66). Provided both transistors deviate in the same manner from nominal characteristics, this provides accurate compensation for variations in the other transistor also.

Apparatus for accurately timing an event relative to clock signals

In a satellite which asynchronously receives radio frequency signals from a lurality of beacons scattered at the surface of the earth, each signal received has a pure carrier wave portion followed by a phase modulated message carrying portion. The frequencies of the signals are not known within a predetermined frequency band. The satellite has a plurality of essentially identical processing units which each receive on their input all the signals present at any given instant in the input frequency band. Each processing unit has a phase locked loop which may be progressively tuned to the frequency of one of these input signals in response to a frequency estimate of this signal to which the operating frequency of the phase locked loop is preset. This frequency estimate is updated until the phase lock occurs on this input signal, ready for demodulation of the message part to begin. The estimate frequencies are derived from an input band frequency spectrum analyzer. A command unit selectively allocates each new frequency estimate to a respective processing unit as a result of a comparison therof with the previously allocated frequency estimates to accelerate the tuning of the processing units and prevent any duplication of the processing of a same input signal.

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Antony, France

Michel Geesen