Showing papers on "Pulse repetition frequency published in 1977"

The statistics of HF sea-echo Doppler spectra

Abstract: Several important statistical properties of the HF sea echo and its Doppler power spectrum, which are useful in optimizing the design of radar oceanographic experiments, are established. First- and second-order theories show that the echo signal (e.g., the voltage) should be Gaussian; this is confirmed with experimental surface-wave data i) by comparison of the normalized standard deviation of the power spectrum at a given frequency with its predicted value of unity, and ii) by cumulative distribution plots of measured spectral amplitudes on Rayleigh probability charts. The normalized standard deviation of the dominant absolute peak amplitudes of the power spectrum (which wander slightly in frequency) are shown from experimental data to be \sim 0.7 for the first-order peaks and \sim 0.5 for the second-order peaks. The autocorrelation coefficient of the power spectra is derived from measured data and interpreted in terms of the spectral peak widths; from this information, the correlation time (or time between independent power spectrum samples) iS shown to be \sim 25-50 s for radar frequencies above 7 MHz. All of these statistical quantities are observed to be independent of sea state, scattering cell size, and relatively independent of radar operating frequency. These quantities are then used to establish the statistical error (and confidence interval) for radar remote sensing of sea state, and it is shown, for example, that 14 power spectral samples result in a sample average whose rms error about the true mean is 1.0 dB.

Method of operating synthetic aperture radar

Abstract: A method, and apparatus for performing the method, of compensating for the effects of Doppler accelerations due to the orientation of the beam in a squinted synthetic aperture radar used for mapping terrain underlying an aircraft are described. According to the disclosed method, compensation is achieved by calculating the Doppler frequency shifts to be experienced by echo signals from points on the terrain to be mapped and then, in accordance with such calculations, varying the pulse repetition frequency of the squinted synthetic aperture radar to eliminate the effects of Doppler acceleration from the echo signals.

Adaptive radar systems and methods therefor

Abstract: Radar systems in which target detection and unambiguously measured range rate are derived from returns from a high pulse repetition frequency (PRF) transmitted waveform; and wherein a lower PRF waveform is adaptively selected as a function of the measured range rate so that the range of even targets, that might otherwise be obscured by clutter, is unambiguously measured. For high PRF track update for a target on which track file data has been established, predicted range is used to adaptively select a high PRF waveform which avoids eclipsing of target returns due to the receiver being non-receptive during the transmission mode.

Amti target/clutter discriminator

Abstract: In an AMTI radar of the type in which the difference between the phase of a current radar return signal and the phase of a radar return signal in a corresponding range bin of a preceding pulse repetition interval (PRI) is averaged over a number of range bins in the range vicinity of the current range bin, phase differences for current range bins are determined as being clutter-like or non-clutter-like by comparison with the previously-determined average phase difference by means of a rectangular distance discriminator which compares the normalized in-phase and quadrature components (cosine and sine, respectively) of the current phase difference with the normalized in-phase and quadrature components of the average phase difference in a rectangular distance discriminator. The rectangular distance discriminator sums the absolute values of the in-phase difference and the quadrature difference and compares them against a rectangular distance discriminant, which in a preferred embodiment is unity. When the summation of the absolute value of the in-phase and quadrature differences exceed the discriminant, the previously-determined phase average components are reintroduced into the phase averaging process; but when it is less than the discriminant, the current phase differences are introduced into the phase averaging process.

Doppler pulse radar with multiple repetition frequencies - transmits blocks of pulses, with pulse repetition frequency being randomly selected

Abstract: The Doppler pulse radar with multiple repetition frequencies has blocks of large numbers of pulses. When radar antenna sweeps fixed point target the transmitter emits a sequence of blocks of successive pulses. Each block contains pulses of same width where the pulses in each block are transmitted at different repetition frequencies. Each block contains the same large number of pulses. During a sequence the pulse repetition frequencies for the blocks are randomly selected.

Radar system employing two kinds of pulses

Abstract: A radar system comprises a first generator for generating frequency modulated transmitter pulses of relatively long duration and a second generator for generating transmitter pulses of relatively short duration, the pulse repetition frequency of the second generator being greater than that of the first generator. The radar system further comprises a receiver having a first receiving channel, containing a pulse compression filter for the detection of return signals from the frequency-modulated transmitter pulses of relatively long duration, and a second receiving channel for the detection of return signals from the transmitter pulses of relatively short duration.

Optoelectronic proximity sensor

Abstract: An optoelectronic proximity sensor having an emitter which directs optical pulses towards a surface as well as a receiver which is oriented toward the point at which the emitted optical pulses impinge on the surface so as to receive a portion of the optical pulses which are scattered back from the surface. The emitter is connected to a pulse generator which causes the emitter to emit the optical pulses at a given pulse repetition frequency. The pulses received by the receiver are evaluated, this being done by a highpass filter which is connected to the receiver and which itself has a limit frequency that is at least approximately equal to the pulse repetition frequency of the pulse generator. A memory circuit is connected to the output of the highpass filter for storing a series of pulses received by the receiver, the arrangement of the parts being such that the memory circuit is rendered capable of receiving the pulses at the beat of the pulse repetition frequency. A control circuit is connected to the output of the memory circuit and puts out an actuation signal when the memory circuit has received a predetermined number of pulses. In practice, the distance sensor is suitable for use with the detonator of a projectile.

Radar beacon apparatus

Abstract: A radar beacon apparatus to be used in conjunction with a search radar during emergency rescue operations. The radar beacon apparatus includes a receiving unit for receiving and detecting a radar pulse wave; a gate signal generating unit for generating upon the detection of a radar pulse wave a gate signal having a specific time interval; a transmitting unit for transmitting a frequency modulated signal which linearly and repetitively changes frequency over a predetermined frequency band during the time interval of the gate signal; and a display unit for displaying the reception of a radar pulse wave. The frequency sweep of the FM signal transmitted by the radar beacon completely covers and overlaps the receiver bandwidth of a comparable search radar, with each beacon transmission having an identical phase and frequency characteristic with respect to prior beacon transmissions. In an emergency situation, the beacon FM transmission produces multiple frequency incursions within the bandpass of the search radar receiver. Due to the constant phase and frequency relationship of these incursions, they are detected and integrated by the search radar to produce a bright display indicative of the position of the radar beacon apparatus. Also, in one embodiment, under normal circumstances the radar beacon operates as a search radar with the beacon transmitter muted while the beacon apparatus displays received radar pulses.

Double sideband pulse radar

Abstract: A pulse radar system transmits a pulse containing an upper and a lower sideband frequency signal. The upper and lower sideband signals are formed by a stable local oscillator signal and a coherent oscillator signal which are mixed in a mixer. The frequency separation between the upper and lower sidebands is sufficient to cause fluctuations in the desired target radar cross section to be statistically independent with respect to the upper and lower sideband frequency components in the transmitted pulse. Target reflected pulses are separately processed for each transmitted frequency component. The probability of detection is improved by mathematically combining the separately-processed output signals of each frequency component.

Side-looking radar systems

Abstract: The invention provides a side-looking radar for use on a moving carrier and for exploring space laterally with respect to the displacement direction of the carrier The receiver includes a non-coherent detector having a reference signal input The average differential phase between the phases of successive received echo pulses appearing at the output of the detector is evaluated and utilised to control a phase shifting arrangement so as to bring the phases of the successive received echo pulses into alignment and establish coherence between the detector and the radar transmitter

Acoustic system for measuring the speed of currents in a body of water

Abstract: An acoustic system for measuring the speed of flow or current speed of a body of water employing a measuring path through the water which extends from one shore to the other in a direction oblique to the direction of flow of the water. A triggerably measuring sound generator positioned on one shore transmits a pulse over the measuring path to a receiver on the other shore. The receiver produces an output which triggers the measuring sound generator to emit a subsequent pulse. A measuring circuit evaluates the resulting pulse repetition frequency of pulses emitted by the sound generator and produces an output proportional to the flow speed of the water.

Coherent pulse radar system with time-shared frequency source

Abstract: A coherent pulse radar system including a switching network for time sharing reference frequency signal from a reference source oscillator between a transmitter amplifier during a transmitting interval, and a local oscillator circuit during a receiving interval.

Limits on pulse repetition frequency in periodically operated CO2 lasers

Abstract: Phenomena responsible for limitation of the pulse repetition frequency in periodic CO2 lasers (isentropic expansion of a heated gas, propagation of shock waves, and presence of boundary layers on electrodes) are considered. The reported calculated results can be used to estimate how individual mechanisms can limit the frequency and average radiation power in specific systems.

Frequency-agile fire control radar system

Abstract: A signal processing system for simultaneously transmitting a plurality of rrier frequencies and receiving certain of said frequencies to the exclusion of others. In a radar system employing the disclosed technique, a CW carrier and pulsed modulated carrier are transmitted simultaneously from a single antenna. The CW carrier and the echo frequency from the modulated carrier are received by a receiver protector circuit which passes the low power echo of the pulse modulated carrier to receiver processing circuitry while suppressing the CW carrier having a power level above a predetermined threshold. The receiver protector enables the use of plural carrier frequencies in a frequency agile system with decreased frequency separation.

Time sharing circuit for guard radar receiver in radar ranging system

Abstract: 1. A time sharing circuit for a multiple pulse repetition frequency, pulsoppler target bearing and ranging radar having dual antenna horns with a receiver and a plurality of range channels coupled in a receiver channel from each antenna horn to a data processor with the plurality of range channels in each receiver channel being in parallel, and having a pulse repetition frequency switching means coupled to control transmission of different pulse repetition frequencies in sequence, the invention which comprises: First and second alternately poled switches in the coupling of said receiver and one range channel of each receiver channel, the switch blade of each switch being coupled to the respective range channel and one pole of each switch being coupled to the respective receiver; Means adding the outputs of said receivers, the summation being coupled to the alternate pole of one of said alternately poled switches; A guard receiver having an output coupled to the alternate pole of the other alternately poled switch; Means subtracting the outputs of said one range channel of each receiver channel, the quotient thereof being coupled to said data processor; and Means for actuating said alternately poled switches by control means of said pulse repetition frequency switching means and said data processor to time share alternate switch positions of said alternately poled switches for different pulse repetition frequencies and to maintain said guard receiver in circuit with the respective range channel when target and jamming signals are received.

The Influence of System Parameters on Acoustic Sounding

Abstract: Acoustic radar records are reproduced to show the effects which may result from varying system parameters such as transmitted power, pulse length, pulse repetition frequency and recording techniques. Improved results can often be achieved by such variation but examples of records which are open to misinterpretation are also given.

Parametric generation of infrared picosecond pulses in LiNbO3 crystals

Abstract: Efficient parametric generation of infrared radiation in LiNbO3 crystals was obtained when these crystals were pumped with the fundamental frequency and second harmonic of a YAG:Nd3+ picosecond laser (the pulse repetition frequency was up to 25 Hz). The maximum energy efficiency of conversion was 17% (the energy of the parametric signal in the 2 μ range was 9×10–4 J) and continuous frequency tuning was obtained in the 1365–4825 and 660–2700 nm ranges (for the fundamental frequency and second harmonic, respectively). The possibility of narrowing the width of the output spectrum by the use of a twocrystal system were considered.

High power variable pulse width triggering circuits

Abstract: The use of high voltage relays in variable pulse width magnetron type triggering circuits are avoided by the use of two separate pulse-forming networks. In addition, two separate banks of charging capacitors and switching transformers are employed. Separate SCR's are employed to apply charging current to either the first or the second bank of storage capacitors. Additional SCR's are employed to initiate the triggering sequence for the selected pulse-forming network and associated circuitry. The selected pulse length might be microsecond or one-quarter microsecond, with pulse repetition rates of 1,000 to 2,000 pulses per second. Accordingly, the duty cycle could be in the order of 0.001%, or less, but the output pulse power during the "on" time for the circuit might be in the order of several hundred kilowatts. During each cycle of operation, the two switching transformers and the output pulse transformer, which are both of the square or rectangular hysteresis loop type, are reset. Other special circuits are provided for preventing adverse interaction between the two high power pulse-forming networks and the circuitry associated with each of them.

Circuit arrangement for controlling the pulse repetition frequency of a signal

Abstract: A circuit arrangement is described wherein the pulse repetition frequency of a signal is digitally controlled in dependence on the pulse repetition frequency of a controlling signal. A presettable digital counter functioning as a frequency divider operates between preset initial and end counts and is reset to the initial value each time the end value is reached; the initial and end values are set responsive to binary signals applied to control inputs of the counter. A bistable trigger stage assumes either an idle or an operative state in dependence on the value of a control signal derived from the controlling pulse repetition frequency and a timing signal. The trigger stage output is used to control either the setting of the afore-mentioned initial value or the end value to produce either too high or too low values for the pulse repetition frequency of the controlled signal.

Musical tone generator system using multiple frequency synthesizers

Abstract: For generating tones in an electronic musical instrument, there are provided multiple master frequency sources, a different source for each octave, differing in frequency from each other by a factor which differs from two by at least one semitone, each of which is coupled to a respective frequency synthesizer all of which have the same dividing ratios, to divide down the frequency of its master frequency source to pitches of the twelve notes in the intended octave. In one embodiment the sources are separate master clock pulse sources, and in another embodiment a pulse train derived from a single clock pulse source is applied to the frequency synthesizer for the highest octave, and the pulse train applied to each of the other synthesizers is derived from the pulse train supplied to the frequency synthesizer for the next highest octave by dividing the pulse repetition frequency thereof by a factor which differs from two by one or more semitones. The result is that temperament errors are randomized by placing them at different interval locations in each octave, and corresponding musical tones of successive octaves are not locked in phase relationship but have frequencies which differ slightly from pure harmonics, so as to present a pleasant chorus effect when such tones are reproduced simultaneously.

Investigation of a laser utilizing self-terminating transitions in europium atoms and ions

Abstract: An investigation was made of the time and energy characteristics of a self-terminating (cyclic) gas laser utilizing europium atoms and ions and operating in a periodic self-heating regime. The active medium was excited by a system based on the Blumlein circuit. The total average radiation power due to atomic transitions was 1.95 W at the optimal (ν=10 kHz) pulse repetition frequency in a tube 2 cm in diameter and 46 cm long. The total average radiation power of the ionic lines was ~10 mW (for the same repetition frequency).

Multiple-pulse thermal blooming and phase compensation

Abstract: Recent experimental measurements of nonlinear, multiple-pulse propagation are presented. Long atmospheric paths were simulated by laboratory scale instrumentation. Blooming was examined as a function of pulse overlap. Observed peak target intensities decreased as the pulse repetition frequency increased and as the effective transverse wind decreased. Theoretical predictions from two computer codes are shown to be consistent with the measurements. A significant fraction of the induced beam distortions were corrected by phase compensation with a deformable mirror.

Pulsed doppler radar station with variable pulse frequency - has digital filter with one shift register for scanning sample processing

Abstract: The digital filter also suppresses permanent echoes, and its characteristic follows changes of pulse repetition frequency. Signals in the shift register (SRG) are at first processed at the timing frequency (fs1) corresponding to the shortest period of the higher pulse repetition frequency, irrespective of the actual pulse frequency. When operating at lower pulse repetition frequencies, supply of input signals and/or further processing of echo signals is blocked during remaining time due to increased period duration. The first time region (T1) is at least equal to the period time of the highest pulse frequency (fp1).

Automatical signalling apparatus

Abstract: An apparatus for receiving a repetitive radar pulse wave signal, generating an ON-OFF signal upon reception of the radar pulse wave signal, and applying the ON-OFF signal to a speaker or a display lamp to indicate the reception of the radar pulse wave.

Clinical digital thermometer circuit - converts voltage drop across temp. sensitive resistor into pulse train, counts pulses and then displays number

Abstract: A temp. sensitive resistor at the body temp. is inserted into a d.c supply circuit and the voltage drop across it, as a function of the measured temp., is converted into a pulse train whose pulse repetition frequency is a function of the voltage drop. The number of pulses is counted by a counter during a specified time interval, and displayed on a decadal display unit. The pulse repetition frequency and the specified time interval are related to one another so that the number of pulses corresponds to the measured temp. in degrees C.

Neodymium-doped YAG laser and generation of intense fourth harmonic of its radiation under pulse-periodic conditions

Abstract: A description is given of a YAG:Nd pulse-periodic laser, assembled from commercially available units and comprising an oscillator and amplifier. This laser can provide efficient frequency conversion and, in particular, generate an intense fourth harmonic with a peak output power of about S MW per pulse (pulse half-width 7 nsec) and an average power of 0.7 W when the pulse repetition frequency is 20 Hz.

A high-stability pulse modulator for Gunn oscillators and amplifiers

Abstract: A pulse modulator is described for frequency-temperature monitoring of transferred electron devices. It has a fully variable pulse height with a stability of 150 mV for a current demand of up to 1 A and is largely unaffected by variations of pulse repetition frequency and pulse width.

Quantization and Saturation Noise Due to Analog-to-Digital Conversion of Radar Returns from Targets with Log-Normal Radar Cross-Section Distributions

Abstract: An analysis of the saturation and quantization noise generated by analog-to-digital (A/D) conversion of radar returns from targets with log-normal radar cross sections is presented. The results of the analysis show that the high-cross-section tails of the log-normal distribution require higher saturation levels to be set in the A/D converter. The setting of the higher saturation level in the converter results in an increase in quantization noise. Thus the minimum achievable distortion in the output of the A/D converter signal is considerably higher than that for radar targets if their radar cross section had an exponential power distribution.