Showing papers on "Pulse repetition frequency published in 1973"

Radio Frequency Pulsewidth Modulation

Abstract: The width of a train of square pulses can be varied to produce a modulated carrier at the pulse repetition frequency. When the pulse train is generated by switching (class D) transistors, highefficiency operation is possible. The efficiency of this type of amplifier can be significantly higher than that of conventional pulsewidth modulation amplifiers, since the switching rate is reduced. In addition, the spectrum of a bipolar pulse train so modulated has the highly desirable property of all spurious products being band limited near the odd harmonics of the carrier.

A Reliable, Repetitively Pulsed, High‐Power Nitrogen Laser

Abstract: The design and construction of high‐power nitrogen 3371 A laser is described in detail. The laser produces 13 mJ at 3371 A in a 12 nsec FWHM pulse at a repetition rate of 5 pulses per second. Various models of the laser have yielded 108 pulses with very infrequent component failure. When a second mirror is added, strong laser action is observed in the N2 first positive system; the total resultant ir output energy is about 3 mJ in a 50 nsec FWHM pulse.

System for resolving velocity ambiguity in pulse-doppler radar

Abstract: A pulse-doppler radar tracking system is disclosed employing four filter channels for tracking range, velocity, azimuth and elevation. Each channel is mechanized in a Kalman filter form by a stored program in a digital computer. The range channel estimates target range, R TPR , range rate, V TPV and acceleration a TPV from one of many received signal frequency spectra at multiples of the pulse repetition frequency (PRF). Once error in the range rate estimate, V TPR , is within a velocity corresponding to λ PRF/4, the velocity channel is reinitialized in its estimate of target velocity, V TPV , with a corrected velocity computed from the less accurate but unambiguous estimate of velocity, V TPR , and the ambiguous estimate of velocity, V TPV .

Harmonic radar helps autos avoid collisions

Abstract: In the foreseeable future, a radar system immune to clutter through use of a special reflecting tag could aid the the driver to maintain a safe distance between the cars, the closing rate, and the driver's ground speed. To eliminate the clutter and blinding problems, a system has been designed that uses an harmonic radar concept. An experimental harmonic radar collision avoidance system has been built using an RCA transferred electron oscillator power source. The measurement of distance was quite repeatable and of adequate accuracy for highway use. In the automatic braking system once the alarm is given, the brake pedal is automatically depressed by a force that increases linearly with time up to maximum pressure until the alarm is removed. The force is then removed linearly with time. The harmonic radar system will reject all blinding signals that it receives other than the second harmonic of its transmitted frequency. The possibility of a false alarm from crosstalk interference is reduced with harmonic radar. The system is adaptable to integrated and printed-circuit techniques. It operates in regions of the frequency spectrum which are still underutilized and spectrum space can be set aside for its future use. The average power density in the immediate vicinity of the antenna is 0.2 mW/cm2. When a dangerous driving situation is detected, an audible warning is sounded and a warning light is flashed. The harmonic radar system provides protection from certain types of rear-end collisions; those where the car in front is in line with the following car. Vehicles that are stopped, but not parallel to the center line, will not be "seen" by the following car because of the purposefully narrow beam of the passive reflector./SRIS/

Doppler Radar with Polarization Diversity

Abstract: In this note we propose a technique to uncouple the tie between unambiguous Doppler velocity and range. Transmission of orthogonally polarized waves in pairs of pulses increases a weather Doppler radar's capability to unambiguously resolve velocity spectrum mean and variance at simultaneous range locations sampled in real time.

Method and apparatus for digitally measuring speed

Abstract: A digital display doppler radar unit has a moving mode and a stationary mode. The incoming doppler signal, which in the moving mode, represents both speed of the radar platform and speed of an approaching target vehicle, is separated into two signal components by selective filtering. One component represents the sum of the ground speeds for the radar platform and approaching vehicles. A time base is generated by a crystal control means and the time base is utilized for correlating the received doppler signals, indicative of speed, with the time base. Each doppler signal component is converted to binary coded decimal (BCD) information and a digital counter counts the cycles of each reeived doppler signal and compares the count with an amount previously stored. Circuit means are provided to validate the received doppler signal, allowing their continual processing only after a preselected number of valid comparisons are made. The radar signal component representing the ground speed sum for the radar platform and the approaching target vehicle, and the component representing radar platform speed are combined. The radar platform speed is subtracted from the combined component, resulting in a digital count representing approaching target vehicle speed. In the stationary mode, there is no radar platform doppler pulses in the radar return and consequently, the returning pulses may be processed directly and no subtracting function is performed. Speeds corresponding to the valid received doppler signals are suitably displayed to indicate a speeding violation.

High pulse repetition frequency electro-optical viewing system

Abstract: A system is provided including a pulsed source of radiation and a gated sensor for responding to optical returns from a predetermined range. A high pulse repetition rate and short duty cycle are employed in order to obtain real time response from the receiver. The receiver is gated with a wave form having a sharp rise time to provide the capability of backlighting selected targets and improving resolution.

Range measurement pulse radar system

Abstract: A multifrequency measurement pulse radar system transmits at least two series of pulses of a same repetition frequency but of different carrier frequencies. The reflected signals are demodulated by a single reference signal and filtered in at least one Doppler filter bank. Each object of the space is characterized by at least two signals, which are picked off separately at the corresponding outputs of the Doppler filters. These signals are compared in pairs in a phase comparator which delivers the range data.

Evaluation of Effects of the Microwave Oven (915 and 2450 MHz) and Radar (2810 and 3050 MHz) Electromagnetic Radiation on Noncompetitive Cardiac Pacemakers

Abstract: Using pacemakers implanted in canines with surgically induced atrioventricular blocks, the effects of the microwave-oven frequencies (915 and 2450 MHz) and two radar frequencies (2810 and 3050 MHz) were evaluated. Quantitative evaluation of these fields with respect to complete inhibition of pacemakers can be made. A narrow zone of inhibition during some exposures-a ``window'' effect-not previously described is reported. The following field parameters would be regarded as potential situations for complete pacemaker inhibition: 1) 915-MHz-fields continuous- and sine-wave modulation at 120 Hz in field strengths over 75 V/m, and 2) fields at either 2810 or 3050 MHz pulsed at a rate of 40 pulses per second (pps) or less with a field strength greater than 250 V/m.

Synthetic Aperture Processing with Limited Storage and Presumming

Abstract: The number of transmitted pulses associated with the Doppler histories of a side-looking radar may greatly exceed the desired azimuth compression ratio of the system. This discrepancy is taxing if the storage required for the azimuth processing is provided by cores, magnetic drums, and the like. Thus, as a practical matter, one considers presumming of the data prior to correlation in an attempt to achieve the desired performance with a minimum amount of digital storage. In this paper, the optimum (in terms of resolution) presummer is derived, along with the optimum apportionment of the available storage capacity between the presumming and correlation operations. Under the condition (or generally pessimistic approximation) that the illumination pattern of the antenna uniformly illuminates a Doppler bandwidth equal to the PRF of the radar, the optimum presumming coefficients are the first Np Fourier coefficients of a function which is one of the Doppler bandwidth to be correlated and zero on the remainder of the PRF bandwidth, where Np is the number of transmitted radar pulses over which presumming is provided. Increasing Np reduces the degradation due to presumming, but may leave inadequate storage for correlation. Hence, we optimize the apportionment between the two operations and present the obtainable resolution as a function of total storage and the number of transmitted pulses in the received Doppler history.

Peaked power coherent pulsed laser transmitter/receiver system

Abstract: In a coherent pulsed laser radar system employing state-of-the-art laser technology, optical technology and microwave radar video signal processing technology, the radar receiver is provided with a bandwidth which is commensurate with doppler frequencies in radar return signals resulting from unresolved target return signal doppler shifts. These unresolved doppler shifts are on the order of magnitude of those resulting from targets having ground speeds on the order of tens of miles per hour. The above said bandwidth being orders of magnitude larger than that required for the data rate of return signals. The pulsewidth of the transmitter is designed to be matched (substantially the reciprocal) to the aforementioned large bandwidth, whose function is determined by the shape of the transmitted pulse. The PRF is chosen to be the lowest possible commensurate with the data rate. In one embodiment, a 10.6 micron carbon dioxide laser transmitter is passively Q-switched by a low pressure gas saturable absorber, such as a sulfer hexafluoride cell, giving an output pulse having a pulsewidth on the order of roughly one tenth microsecond to one microsecond, and the receiver has bandwidth of approximately one half to three MHz, operating at a nominal IF center frequency of 30 MHz, with receiver information rates on the order of 20-50 KHz, the local oscillator being adjusted with respect to the ground velocity of the laser radar so as to provide radar video at substantially the IF frequency falling within the bandwidth, as described hereinbefore.

Electrooptic switching in oriented liquid-crystal films

Abstract: A study was made of the phase and amplitude modulation characteristics of the light passed through oriented films of nematic liquid crystals with a positive permittivity anisotropy. The polarization method was used to record changes in the phase delay of light under the action of voltage pulses. The dependence of the optical response on the amplitude and duration of these pulses was determined, switching rates of several kilohertz were achieved by partial reorientation of the molecules in the crystals. Pairs of positive and negative pulses made it possible to eliminate the influence of the pulse repetition frequency on the modulation conditions and to increase the switching rate.

Method and modulation system for ambiguity reduction in pulsed radar

Abstract: The modulation system of a pulsed radar includes a modulator having a generator for providing a radar pulse repetition frequency (PRF) signal and which pulse modulates a single frequency oscillator to develop a pulse modulated signal. The PRF signal also drives a divider circuit that creates a divided control signal in phase coherence with the PRF signal. The divided control signal enables a linear sawtooth frequency modulated (FM) oscillator to provide an FM signal having a modulation rate which is a submultiple of the PRF. The total deviation of the FM signal is a function of the PRF. A mixer circuit combines the FM and pulse modulated signals, and the sums of the frequency components thereof are selected by a filter to provide a modulated output signal which is suitable for being transmitted by a radar either directly or on a carrier. The modulated signal rotates the time-frequency plane of the pulse modulation ambiguity response pattern of the radar with respect to the amplitude axis so that unwanted ambiguities are shifted off of the time and frequency axes to facilitate velocity and range measurement.

Perspective radar display using linear vertical sweep

Abstract: A perspective radar display is provided on a cathode ray tube having a linear vertical sweep by feeding the video echo return signals to the video input of the cathode ray tube in a nonlinear manner as opposed to vertically sweeping in a non-linear manner. Essentially, the video signals are stored linearly with time during a first time interval corresponding to the time interval between successive transmitter triggering pulses defining the radar pulse repetition frequency, and then released to the video input of the cathode ray tube hyperbolically with time over a second time interval measured from the beginning to the end of a vertical sweep so that the signals are passed to the cathode ray tube at a faster rate during the later portion of the sweep as compared to the earlier portion to thereby provide a perspective display.

Radar receiver for detecting coded information buried in radar echoes

Abstract: An IFF radar system having a processor for analyzing radar reflections to termine if the reflections were artificially modulated by a cooperative target in accordance with some predetermined code. The processor ignores modulations in the radar reflections due to Doppler shifts. The amplitude of the detected target return is sampled and held in the radar receiver. The resulting signal is fed to the processor. The signal is then (half or full wave) rectified, the DC removed and then correlated in a multiplier with the predetermined coded signal, which is generated in the processor. The output of the multiplier is then integrated. If there has been a modulation of the reflected energy exactly in accordance with the predetermined code, then the output of the integrator will increase to a point detected by a threshold device. Although there will be modulations in the received signal due to the Doppler effect, the rate and phase of these modulations will be such that the time integral over a given time will be small or nonexistent.

Multiple target indicator and discriminator

Abstract: A multiple target indicator and discriminator is provided for use on a tracking radar of the sequential lobe type. Multiple targets occurring within one radar beam-width cause the radar return signal to have a phase modulated component at the scan rate frequency and also an additional second harmonic, amplitude modulated component at twice the scan rate frequency. These modulated components are detected and removed from the radar return signal and used to provide a multiple target indicating signal. These modulated components are also used to produce an angle bias signal which, when added to an angle error signal in the radar angle track loop, causes the radar to track only one target in a formation of targets. Since the angle bias signal is developed directly from either the phase modulated component or the amplitude modulated component of the return signal produced by the multiple targets, such bias signal is responsive to any change in target reflectivity and thereby provides an adaptive angle bias signal.

Pulse train modification circuit

Abstract: For the purpose of indicating the total volume of fluid flow in a pipeline corrected to 60* (Fahrenheit) barrels, the pulse train output of a turbine flowmeter is corrected for temperature by eliminating every tenth pulse leaving sets of nine and adding a number of pulses to the sets of nine, which number is directly proportional to that contained in an analog-to-digital converter storage register. The converter is connected to circuits which produce a D.C. voltage proportional to the temperature of the fluid. An inverter, two differentiators and an OR gate are employed to produce pulses at a pulse repetition frequency (PRF) twice that of the incoming pulses. The pulse adding circuit has a set of first, second . . . eighth AND gates which receive pulse trains of pulse repetition frequencies f, f/2, f/4, f/8, f/16, f/32, f/64, and f/128, respectively, where f is twice the PRF of the incoming pulses. The first, second . . . eighth AND gates are controlled by the first, second . . . eighth flip-flop in the register, where the first, second . . . eighth flip-flops correspond to the most, next most . . . least significant digits of the number contained in the register. An insertion circuit adds the pulses to the sets of nine at a time T/2 before and/or after one pulse in one set of nine, where T f/2. A divide-byten divider is connected from the AND gates to reduce the number of added pulses so that they vary the average number of pulses recorded by a counter that counts the sets of nine plus the added pulses. The number of counted pulses then can vary from 90 percent to about 110 percent of the incoming pulses for register binary numbers from zero to 11111111. An indicator is connected from the counter to indicate the count thereof.

A Systematic Approach to Blind-Speed Elimination

Abstract: In radars that achieve a high subclutter visibility by coherent processing over several pulses, a serious problem appears in the form of blind Dopplers, or "speeds," at which target detection is impossible. Of the possible methods of eliminating these blind speeds, the most basic one that is employed when the performance requirements are high involves the use of several PRF's. These PRF's are chosen so that coverage is obtained at any Doppler with at least one PRF. The problem faced by the radar designer is to select the set of PRF's and the pulse numbers for each PRF so that the search frame time is minimized. This paper evolves a systematic method for the design of the blind-speed elimination scheme. A formalized approach is offered that shows the possible combinations of wavelength, PRF, and pulse number and the tradeoffs involved, without introducing the confusion ordinarily associated with multiparameter choices.

Prf detection system and method

Abstract: A pulse repetition frequency (PRF) detection system is provided for indicating the existence of pulse trains having predetermined repetition frequencies in a composite signal containing pulse trains of different pulse repetition frequencies. The system includes a plurality of independent sorters to which the composite signal is sequentially applied. Each of the sorters is operable to detect a pulse train having a predetermined pulse repetition frequency, to indicate the detection, and to produce pulses for inhibiting or blocking the application of the corresponding pulses of the composite signal on a pulse-by-pulse basis. The sorters may be arranged and interconnected in a decreasing order of frequency detection whereby the signal applied to each successive sorter has all higher frequency detected pulse trains removed therefrom.

Bandwidth measurement system

Abstract: A signal source producing signals of selectively determinable variations in repetition frequency drives a step-recovery diode circuit for generating signals having spectral frequency distributions varying in response to changes in the repetition frequency. The spectrally distributed signals are impressed upon the circuit under test and a wide band amplitude modulation detector is connected to the output of the circuit under test. As the pulse repetition frequency is gradually changed, the output of the detector is observed, and the highest pulse repetition frequency producing signals detectable by the detector is a measure of the bandwidth of the circuit under test.

High-average-power xenon laser

Abstract: A transversely excited pulsed Xe laser producing over 10 W of average multiwavelength infrared power at a pulse repetition frequency of 1.2 kHz is described. A diffraction grating allows single-line operation at 2.03, 2.65, 3.43, or 3.65 μ.

Decadically adjustable frequency synthesizer

Abstract: A variable-frequency oscillator works through a pulse shaper, a pulse-rate modifier and a frequency divider of step-down ratio n: 1 into a phase comparator also receiving the output of a generator of reference frequency f. To adjust the operating frequency F of the oscillator at a selected value F nf + OR k, a pulse train of repetition frequency or cadence k is fed to the pulse-rate modifier to reduce or augment the number of pulses per second reaching the divider. The modifying pulse train may be derived from one or more stages of the frequency divider, from a step-down network driving the reference-frequency generator, an independent pulse source.

Radar fuzing system

Abstract: A frequency modulated continuous wave radar signal is transmitted to a tat and the signal reflected from the target is compared with a sample of the continuous wave transmitter to produce a difference frequency signal. The difference frequency signal is band-pass amplified, wide-band limited, and processed by two frequency discriminators displaced from each other in the frequency domain, but both within the frequency band of the limiter and band pass amplifier. Detectors, integrators, and thresholding circuits determine, with suitable false alarm rates, in which half of which discriminator the difference frequency signal is concentrated.

Resonance damage process

Abstract: A method and system for the production of stress waves in a solid target employs a pulsed source of coherent photon energy. the pulse repetition frequency of the photon energy is chosen in dependence upon the physical dimension and nature of the selected material so as to reinforce reflected compression and rarefaction waves within the material.

Radar recording and reproducing system with pulse modulation and time division multiplexing

Abstract: A record and reproduction system for a forward-looking radar. Video, blanking, horizontal and vertical deflection signals are recorded directly from a radar receiver on a single wideband tape track. A composite signal of the radar receiver information is formed by pulse width modulating the deflection signals which are time multiplexed into the blanking interval preceding the video signal. On playback, the composite signal is demultiplexed and the video and deflection signals recovered for direct radar display of in-flight data.

Autocorrelation and Power Measurement with Pyroelectric and Dielectric Bolometers

Abstract: A pulse comparison technique is described which yields the autocorrelation function and the power spectrum of a repetitive time-domain waveform. The autocorrelation function is realized with a sliding short in a coaxial transmission line to provide time delay; a pyroelectric bolometer to provide multiplication through a square law voltage response; and a capacitor to provide integration. Problems of realization of a perfect time delay and integration limitations are considered, and it is found that noise fluctuations yield the main time resolution limitation that is equivalent to 8 ps for 15-V pulses and a 50-s integration time. The pyroelectric voltage-sensing bolometer is then compared to a pyroelectric capacitance sensing bolometer. It is shown that the capacitance sensing bolometer can handle much longer pulse durations than the voltage sensing bolometer. It is also demonstrated that the sensitivities of the two techniques are equivalent in a typical case at a capacitance sensing bolometer bridge voltage of 3 V. Measurement results of the autocorrelation function and power spectrum, using a voltage sensing pyroelectric bolometer, are given for a nominal 15-V, 500-ps time duration, whose baseband pulses have a 100-pps (pulses per second) repetition rate.

Self-mode-locking in the helium-selenium laser

Abstract: Self-mode-locking of low-order transverse modes is reported for six strong laser transitions of a cataphoresis-type helium-selenium laser at the wavelengths 49757, 49928, 50687, 51760, 52275 and 53054 A. The self-mode-locked pulse repetition frequency is a multiple n of the cavity axial mode separation frequency c/2L, with n=3, 4 or 5, depending on the transition. This effect is attributed to the reduction in the number of oscillating modes by axial mode competition, resulting from hole-burning and cross-relaxation.

Clutter Spectra of Low PRF AMTI Pulse-Doppler Radar

Abstract: Approximate expressions are derived for the video clutter spectra in the receiver of a low pulse repetition frequency (PRF), airborne moving target indicator (AMTI), pulse-Doppler radar for both step-scanning and continuous-scanning antennas. The receiver is assumed to process the received waveform with a clutter-tracking oscillator and a window function is employed to obtain short-term spectra. Except for the broadening effects of the window function, it is shown that the clutter spectrum can be simply related to the antenna voltage-gain pattern. It is further shown, in the scanning antenna case, that the combined spectral broadening due to platform motion and antenna scanning cannot be assumed to be the result of the convolution of the separate effects unless the antenna gain pattern has a Gaussian shape. The approximate clutter expressions are illustrated by examples and are shown to agree well with the results of computer calculations.

Matched filter for radar utilizing spin-echo techniques

Abstract: A matched filter for providing correlation between an RF coded radar pulse and the target return signal by means of a plurality of spin-echo elements which are sequentially range gated ''''on'''' for a time substantially equal to the radar pulse length during the target signal return time after having been ''''set'''' during the radar pulse transmission time so that the noise occurring within the RF signal bandwidth is incident during one but not more than two consecutive range gate time periods with the resulting effect that noise is reduced to the point where it has the same effect as it does upon conventional matched filters utilized for radar applications.

Heat pipe copper vapor laser

Abstract: : The program objective was the development of a copper vapor laser in which the copper was contained within a heat pipe and whose vapor density could be controlled by an inert gas. Successful operation of a heat pipe with graphite and tungsten as the materials of construction was obtained to temperatures of 2100C. Both helium and argon were used for the control of the copper vapor pressure. The second aspect of the program was the development of a discharge configuration capable of the production of high current, short risetime excitation in the vapor and compatible with the heat pipe structure. Pulse generators were developed which were integral with the laser structure and had variable pulse repetition rates from one to 10,000 pulses per second. In the third part of the program investigation of laser action obtained in the heat pipe was carried out. Laser action at both 5106 micrometers and 5782 micrometers was successfully demonstrated at temperatures between 1500C and 1900C. Multiple laser pulses resulting from a single excitation pulse have been observed at temperatures above 1700C with pulse widths less than 2.5 nsec (bandwidth limited).