Showing papers on "Pulse repetition frequency published in 1975"

High-performance electrotherapeutic apparatus

Abstract: Improved electrotherapeutic apparatus comprises A. an electromagnetic energy radiating head including primary and secondary coils and a capacitor electrically connected across the secondary coil, B. and an input circuit including a source of high frequency oscillations, a power amplifier and a control circuit for creating and transmitting to the head a sequence of pulses of high frequency electrical energy and for controlling the amplitude of the pulses and the intervals therebetween, the pulses having substantially rectangular shape and having a repetition rate and duration characterized in that they define a duty factor of between 0.35 and 0.55, where (duty factor) = (pulse repetition rate in pulses per second) × (pulse duration in micro seconds).

Avoidance by rats of illumination with low power nonionizing electromagnetic energy.

Abstract: Rats spent more time in the halves of shuttle boxes that were shielded from illumination by 1.2 GHz microwave energy than in the unshielded. In Experiment 1, rats avoided the energy when it was presented as 30-musec pulses with a pulse repetition rate of 100 pulses per second (pps). The average power density was about .6 mW/cm2, and the peak power density was about 200 mW/cm2. In Experiment 2, the energy was presented both continuously and in pulse-modulated form, i.e., .5-msec exponentially decaying pulses at a rate of 1,000 pps. The average power density of the continuous energy was 2.4 mW/cm2, and the average power density of the pulse-modulated energy was .2 mW/cm2. The peak power density of the modulated energy was 2.1 mW/cm2. The rats avoided the pulsed energy, but not the continuous energy.

A compact sealed pulsed CO 2 TEA laser

Abstract: A compact sealed pulsed CO 2 TEA laser with an operational life exceeding 106pulses has been developed. It provides single-mode output pulses of 1.0-MW peak power in 50-ns full width at half maximum (FWHM) and total energy 110 mJ in 2 μs. The output beam emerges from an 8.5-mm-diam aperture with a full-angle divergence of 3.5 mrad, which is less than 1.5 times the diffraction limited value. With a different optical resonator system, the corresponding multi-mode output exceeds 1.4 MW in 80 ns with a total energy of 300-500 mJ delivered in 4 μs and with a beam divergence of about 10 mrad. These output levels, corresponding to 15-25 J/l, are obtained for a pulse repetition frequency of 2 Hz and are maintained after initial conditioning, even in lasers tested to 2 \times 10^{6} pulses. Hitherto, prolonged sealed operation was not possible because the glow discharge degraded into arcs. This has been overcome in the present device by the addition of small quantities of carbon monoxide and hydrogen to the basic CO 2 -N 2 -He-laser gas mixture before seal-off.

Frequency diversity sidelobe canceller

Abstract: A new system and technique for cancelling interference in frequency agile ceiving systems Main and auxiliary signals are supplied to a pair of multiple loop side-lobe cancellers which are capable of being tuned to different frequencies At the same time, under the control of a timing clock, plural frequencies are selected and multiplexed between two channels at the time of a radar pulse transmission The side-lobe cancellers and radar are coupled to the channels such that each caneller operates at a given frequency for two consecutive pulse periods, with the radar transmitting at said given frequency during the second pulse period By continuously cycling between the two channels, each canceller is operating at the proper frequency to cancel interference even though the radar is changeing frequency on a pulse to pulse basis

Apparatus for controlling the feed rate and batch size of a material feeder

Abstract: Apparatus for controlling the feed rate and batch size of the material feeder is disclosed. A signal generator computes the weight of material delivered by the material feeder and compares it to first and second presettable values. When the weight of material delivered by the feeder is less than the first presettable value, the signal generator enables a first pulse generator which generates a pulse train having a relatively high pulse repetition frequency. This pulse train is applied to a motor speed controller which causes the feeder to deliver material at a relatively high rate. When the weight of material delivered by the feeder reaches the first presettable value, the signal generator enables a second pulse generator and disenables the first pulse generator. The second pulse generator generates a pulse train having a pulse repetition frequency substantially lower than that of the pulse train generated by the first pulse generator. The second pulse train is also applied to the motor speed controller which then causes the feeder to deliver material at a relatively low rate. Finally, when the weight of material delivered by the feeder reaches the second presettable value, the signal generator generates an end of batch signal which disenables the motor speed controller and causes the material feeder to stop delivering material.

Pulse coherent transponder with precision frequency offset

Abstract: A radar reply transponder for use with existing radar tracking systems wherein a reply pulse is generated and trasmitted in response to an associated interrogation pulse. The reply pulse is delayed in time and offset in frequency by a precise amount with respect to the interrogation pulse, but it is nevertheless phase coherent therewith so as to preserve the required Doppler frequency information and thereby permit accurate velocity measurements. Phase coherence is effectively maintained by utilizing a single continuously operating local oscillator for down-converting the received interrogation pulse to an intermediate frequency as well as up-converting the signal information to provide the delayed and frequency offset reply pulse. The precision frequency offset is obtained by switching in an additional reactance element in the oscillator-determining circuitry during the time up-converting is being effected. The radar transponder may thus be used in a high-vibration environment with no substantial introduction of error in velocity measurements caused by using two independent oscillators to formulate the frequency offset.

Radar detection of turbulence in precipitation

Abstract: A technique for processing the IF portion of a radar return signal in ordero provide the remote detection and measurement of atmospheric turbulence occurring within precipitation. The technique employs an amplitude limiter, a wideband discriminator and a video amplifier to provide real time measurement of the precipitation velocity. A velocity comparison at various radar ranges is made to provide an indication of the turbulence. The analog circuit employed to make this measurement operates with high speed and is capable of being used with any pulsed (coherent or non-coherent) weather radar.

Frequency spectrum analyzer

Abstract: A frequency spectrum analyzer adapted for use in a real time signal processing radar system is disclosed. In such system a plurality of sets of radar returns, each one of such sets corresponding to radar returns from objects disposed in each one of a like plurality of range cells, is stored in a time compressor section, the radar returns in each one of the sets thereof being stored at the pulse repetition frequency (PRF) of such radar system. After storage of such radar returns, a like plurality of chirp pulses is produced, each one of such pulses having a dispersive time Kτ. Synchronously with each one of the chirp pulses, one of the plurality of sets of stored radar returns is retrieved from the time compressor section, in a time duration equal to Kτ. Each one of the retrieved sets of radar returns is mixed with a corresponding one of the plurality of chirp pulses to produce a series of mixed signals which is coupled to a pulse compressor. Each one of the mixed signals is compressed into a pulse occurring at a time related to the Doppler frequency of any object in the range cell producing such associated radar returns. The time compressor section is used prior to pulse compression to effectively "match" the radar dwell time, generally several milliseconds in duration, to the dispersive time of the chirp pulse, generally several microseconds in duration, thereby enabling the pulse compressor to include a practical surface acoustic wave (SAW) delay line. Further, the "compressive" bandwidth, β, of the pulse compressor is equal to, or greater than, the dispersive bandwidth of the chirp pulses, thereby to maximize the power in the compressed pulses. Means are provided to adjust the dispersive time of the chirp pulse, thereby to correspondingly adjust the effective number of frequency resolution cells of the frequency spectrum analyzer.

Optical processing of pulsed Doppler and FM stepped radar signals.

Abstract: A real-time radar processor with an electron beam addressed KD(2)PO(4) light valve as the input electrical-to-optical transducer is described. The input format, output plane pattern, and the required optical processing of pulsed Doppler and FM stepped radar data on this system are discussed. Experimental output plane patterns with actual radar data are presented. Although these data are processed off-line, the processing is performed at real-time data rates.

Circuitry for use with an ionizing-radiation detector

Abstract: An improved system of circuitry for use in combination with an ionizing-radiation detector over a wide range of radiation levels includes a current-to-frequency converter together with a digital data processor for respectively producing and measuring a pulse repetition frequency which is proportional to the output current of the ionizing-radiation detector, a dc-to-dc converter for providing closely regulated operating voltages from a rechargeable battery and a bias supply for providing high voltage to the ionization chamber. The ionizing-radiation detector operating as a part of this system produces a signal responsive to the level of ionizing radiation in the vicinity of the detector, and this signal is converted into a pulse frequency which will vary in direct proportion to such level of ionizing-radiation. The data processor, by counting the number of pulses from the converter over a selected integration interval, provides a digital indication of radiation dose rate, and by accumulating the total of all such pulses provides a digital indication of total integrated dose. Ordinary frequency-to-voltage conversion devices or digital display techniques can be used as a means for providing audible and visible indications of dose and dose-rate levels.

Marine radar transmission and reception system

Abstract: A marine radar transmission and reception system in which first and second transmission pulse radar waves are emitted as first and second pulse radar waves from first and second radar antennae or a common radar antenna; reflected waves of the first and second emitted pulse radar waves are received as first and second received pulse radar waves by the first and second radar antennae or the common radar antenna; the modes of the first and second transmission pulse radar waves are selected in cooperation with those of the first and second radar antennae or that of the common radar antenna so that the first and second received pulse radar waves may be received by the first and second radar antennae or the common radar antenna independently of each other; a quotient or difference output corresponding to the quotient or difference of the first and second received pulse radar waves or the first and second received outputs based thereon is obtained; and sea clutter eliminated received pulse radar waves or outputs based thereon that signal components of the period--in which the quotient or difference output exceeds one predetermined threshold value or lies between two threshold values--are eliminated or suppressed, are obtained.

Means for real-time laser source characterization

Abstract: A system for fully characterizing monochromatic radiation incident on the stem. The system computes the azimuth and elevation of the point of origin, optical frequency, pulse width, power level and pulse repetition frequency of the source.

Laser utilizing Cu I transitions in copper halide vapors

Abstract: Stimulated emission at a high pulse repetition frequency was obtained as a result of self-terminating transitions in the copper atom in CuCl and CuBr vapors. The repetition frequency was equal to the excitation pulse frequency (16.5 kHz). The efficiency of the CuBr laser was ~1%. The average output power in the form of the λ = 510.5 and 578.2 nm lines was 12 W. The stimulated emission was observed in 12, 18, and 30 mm diameter quartz discharge tubes.

Adaptive clutter velocity cancellation system for pulsed digital MTI system

Abstract: A digital MTI radar system for improved handling of "moving clutter" which employs a double phase detector scheme to provide both Doppler sine and Doppler cosine terms which are separately digitally encoded in a series of range increments throughout each pulse repetition interval. The discrete digitally encoded values thus represent instantaneous echo signal phase angle in each corresponding range increment. This angle data is compared by range increments with that of the last previous pulse repetition period, to provide net signal phase angle change in digital form (a velocity related term) by range increments successively. The remaining circuitry comprises a device for sampling this net phase angle change over a predetermined number of range increments to compute average clutter velocity with respect to the radar system location. A bona fide signal in the moving clutter may then be recognized on the basis of its exceeding the average clutter velocity. A quantized output is effected by means of a logic arrangement which detects the condition of signal presence in one or two adjacent ones of the range increments provided these increments are preceded and followed by a predetermined relatively small number of range increments exhibiting no signal above the said average clutter velocity.

Radar for short range measurements

Abstract: In a radar installation for measuring distances by transmitting and receig signal modulated by sequences of pseudo-random bits, generation both of the sequence of pseudo-random bits and of corresponding sequences with which the received radar signal is correlated, is controlled by a variable frequency clock. The frequency of the clock is varied to maximize the peak of the correlation function and the resulting frequency used to indicate the radar-target distance.

Pulse radar method and system

Abstract: A pulse radar system which is designed for installation on a vehicle. A control pulse generating circuit is triggered by the trailing edge of a transmitting pulse to generate a pulse train consisting of 8 time-divided pulses which in turn are supplied to a distributor. Simultaneously, the echo of the transmitted pulse is demodulated and the resulting signal is applied to the distributor so that depending on which one of the 8 divided pulses corresponds to the applied demodulated signal, the distance to the target is displayed on the corresponding indicator.

High resolution sector scan radar

Abstract: A high resolution, azimuth sector scan radar is provided with sinusoidal operation to establish time sequencing of the radar main bang signal with the horizontal and vertical deflection signals of the video display and the antenna azimuth sweep. A high frequency master oscillator provides a fundamental sinusoidal signal to establish the pulse repetition rate of the radar main bang signal, while phase shift networks provide phase shifting of this signal to produce variable time delayed sinusoidal signals for the vertical deflection excitation and video unblanking of a CRT, to permit the display of selected range segments within the maximum range of the system. A submultiple frequency of the fundamental pulse repetition frequency signal, is synchronized with this signal and is used through similar phase shifting functions to provide video unblanking for the azimuth component of the display, horizontal deflection excitation for the CRT, and synchronization of the radar system and the radar antenna azimuth drive. The radar system features the use of simplified circuitry to produce the control timing, CRT deflection signals, and antenna azimuth sweep synchronization, to provide a system having small size and weight characteristics and being suitable for airborne use.

Velocity discrimination radar

Abstract: A radar method and apparatus which utilizes a first frequency signal modued by a first modulating signal and a second frequency signal modulated by a second modulating signal, the first and second frequencies being different and the first and second modulating waveforms having different periods of repetition. The radar receiver separates the return radar signal into the component due to the first frequency signal and the component due to the second frequency signal. Both components are then heterodyned with their respective frequency signals. Each modulating waveform is subjected to a plurality of delays and each component is subsequently correlated with each of its respective delayed modulating waveforms. A target is recognized when the correlated first frequency component exceeds a predetermined threshold and simultaneously the correlated second frequency component exceeds a predetermined threshold.

Effect of composition and forming parameters on the conductance of amorphous chalcogenide threshold switches

Abstract: The effect on the conductance of formed STAG threshold switches of changing both the composition of the virgin films and the ON time of the switching pulse during the forming process has been studied. It was found that the silicon content of the glass has a large effect on the activation energy and conductivity parameters of virgin devices. After forming, the conductance of the device is much higher than in the unformed state; however, silicon no longer controls the conductivity parameters. When switching STAG threshold switches it was found that increasing the ON time of each switching cycle causes a decrease in the conductance of the formed device from its value when formed with very short ON times. For low pulse repetition frequencies the conductance saturates for ON times typically greater than 100 μs. The rate at which the conductance decreases is dependent upon the silicon content of the virgin glass. For high pulse repetition frequencies the conductance initially falls, following the low pulse repetition frequency case, and then rises, finally locking on to a memory state. The observations have been explained in terms of an initial large structural change of the glass, caused through adiabatic heating during switching. Relaxation of this structure back to more stable glass phases is possible during the ON time if the ON state temperature is sufficiently high. For high pulse repetition frequencies the temperature of the device is much higher, allowing for the possibility of crystalline growth. This leads to an increase in conductance and eventual lock on.

Copper vapor laser operating at a high pulse repetition frequency

Abstract: An investigation was made of the optimal conditions for the operation of a copper vapor laser emitting at 510.6 and 578.2 nm. Stimulated emission was obtained as a result of a discharge in an Ne–CuI mixture. A simple power supply system ensured a stimulated emission pulse repetition frequency of 30 kHz.

System for precision time measurement

Abstract: A system for measuring a first period of time, for example a period between a pair of pulses, with an extraordinarily high degree of accuracy. Two ramp voltages of different slopes are started in synchronism with the first occurring pulse. The ramp with the largest slope is then sampled and held on receipt of the second occurring pulse. A counter counts a clock of a moderate pulse repetition frequency (PRF) during a second period occurring between the time the ramps are started and the time the amplitude of the ramp of the smaller slope becomes equal to the sampled amplitude of the ramp of the larger slope. The count stored in the counter at the end of the second period is then directly proportional to the first period or is equal thereto. Moreover, the count can be far more precise than it would be by counting the clock PRF during the first period. By making the larger ramp slope 1,000 times as large, for example, as the smaller ramp slope, the precision of the measurement may be increased 1,000 times for the same clock PRF.

Method for providing means to eliminate ambiguous polarization effects on phase and amplitude of radar backscatter due to unknown target aspect angle

Abstract: A radar system is operated in a manner that provides determination of the coincidence of radar signal polarization with the major axis of a target of unknown aspect angle. This information so obtained can be utilized to enhance radar signals or to improve target identification capabilities. One approach comprehends transmitting circularly polarized radar signals and receiving return signals on a linearly polarized receive antenna. By varying the polarization of the receive antenna over a 180° range signal maxima and minima are detected that correspond to alignment of the target's major axis with the radar signal E and H field vectors. The method can also be practiced by transmitting linearly polarized radar signals, the polarization of which is also varied over a 180° range.

Improvements to pulsed Doppler radars

Abstract: The invention relates to a coherent pulsed Doppler radar system operating at a medium pulse repetition frequency. The pulses are emitted in a repetitive sequence b of blocks of recurrent pulses. The repetition frequencies of the blocks are randomly distributed over the range of medium repetition frequencies. The radar system is coupled to a fast elevation-scanning antenna which carries out b elevation scans covering a zone comprising q resolution cells in elevation and one resolution cell in bearing. Application to airborne surveillance radars.

Methods of and apparatus for simulating ultrasonic pulse echoes

Abstract: Methods of and apparatus for simulating ultrasonic pulse echoes are used to test and calibrate ultrasonic flaw detectors by simulating a train of radio frequency pulses, having a pulse repetition frequency which is indicative of both the speed of sound in a material under test and the thickness of that material. This is accomplished by generating a train of d.c. pulses having a pulse repetition frequency, which is directly proportional to and, which is a multiple of the speed of sound of the material The pulse repetition frequency is also inversely proportional to the thickness of the material. The d.c. pulses are used to drive a radio frequency pulse generator and a pulse modulator. The outputs of the radio frequency generator and pulse modulator are then combined to produce a signal having an amplitude envelope, which simulates a series of ultrasonic pulse echoes.

Black and white and colour TV transmission system - can be coded by PAL or NTSC system

Abstract: Additional two-channel sound signals are transmitted in horizontal blanking periods and scanned at twice the line frequency. They are transmitted in digital form during back porch extended by shortening of the synchronisation signal. Pulses have a repetition frequency of the colour carrier, and its phase is equal to that of the latter. Colour synchronisation signal for decoding is recovered by evaluation in the receiver of the sound signals, using the same clock pulses in sender and receiver. A control derives these pulses from the sound signal pulse repetition frequency. The control unit has a counter for the pulses and divides each line period into four equal sections. A logic network delivers clock pulses necessary for each scanned value processing.

Analysis of a dual-frequency moving target indication system

Abstract: The problem of a two-frequency m.t.i. system is formulated for a general case. It is concluded that: (a) The two-frequency m.t.i. system sees an increased clutter Doppler variance as compared to that of a single frequency system. (From σ2 to σ2(1 + r2) where r is the ratio of the carrier frequencies in the two frequency channels.) (b) The mean clutter-Doppler frequency, at the same time, is reduced accordingly from f0 to f0(1 − r).

AC switch speed control for two phase motors

Abstract: A variable burst length, switching system for controlling speed and direction of rotation of a two phase AC motor is disclosed. A bipolar DC command or error signal is supplied to a pair of pulse width modulators, one of which, depending on the DC signal polarity, produces a first pulse train of which the ratio of pulse duration to pulse repetition interval or average value is indicative of the required motor speed. The first pulse train is supplied to synchronization means which generates a second substantially identical pulse train wherein the leading and trailing edges of the pulses are timed to occur in a fixed time relationship with the energization voltage for the motor. The second pulse train comprises the input signal to current control means which is operable to energize the motor.

Automatic frequency control circuit for frequency agile radar

Abstract: An automatic frequency control circuit for frequency agile radar systems. Fundamentally, the invention utilizes two oscillators of different frequencies and which are controlled by the IF pulse envelope. The outputs of the oscillators are monitored until such time that corresponding transition points of the outputs coincide. A counter, receiving the output of one of the oscillators, is then decoded at the time of coincidence and the resulting value, being a function of deviation of the IF pulse from a desired frequency, is applied to the radar system as an error correction signal.