Showing papers on "Pulse repetition frequency published in 1974"

Radar system having quadrature phase detector compensator

Abstract: Method and apparatus are disclosed for correcting amplitude and phase imbalances between the "in phase" and "quadrature" channels of a digital signal processor by determining a correction coefficient from a test signal periodically introduced into the quadrature phase detector of a radar system. The frequency spectrum of the signal at the output of the phase detector in response to each such test signal is utilized to produce a correction coefficient for application to radar return signals passing through the phase detector during normal radar operation, thereby providing true quadrature radar return signals for digital processing.

Location and recognition of discontinuities in dielectric media using synthetic RF pulses

Abstract: RF pulses are used in radar and sonar to detect and locate targets in extended media. Short RF pulses (and impulses) can be used to find buried objects or voids by echo sounding, or can be used to probe snow fields or the depths of the earth. Although similar to radar in principle, there are important differences in these applications that can lead to significant variations in the design approach. A novel system is described, with a computer-programmed tunable RF source, that tunes rapidly through all the frequencies of a nanosecond pulse spectrum, makes individual "CW" measurements, stores them, and finally computes a synthetic echo. Target signatures can be "recognized" by calculating correlation functions. Experimental results are presented.

Pulse type radar system

Abstract: The present invention relates to a radar system haing a high range resolution. Said radar system emits series of n pulses whose carrier frequencies are distributed within a band B and whose time positions are associated with the frequency in accordance with a linear reelationship. The echoes received in return are demodulated with the corresponding waves which gave rise to them, and supplied to a filter bank which produces at different outputs, different signals which correspond to separate objects or parts of objects.

Analysis of experimental NRL radar altimeter data

Abstract: An X-band radar designed and built by the Naval Research Laboratory and capable of continuously variable transmitted pulse durations down to 1 nsec is being flown on a NASA Wallops Flight Center C-54 aircraft to investigate the interaction of radar altimeter signals with the sea surface. There is good agreement between the observed radar altimeter leading edge rise time for a 1-nsec transmitted pulse and the rise time predicted from the radar parameters and the sea state determined by a laser profilometer. Using a threshold tracker on 29-pulse averages for a transmitted pulse of 24 nsec, we found that the range noise varied linearly with the power level of the threshold over a considerable range. The altimeter range quantization was 9.35 cm and a minimum range noise of 3.9 cm was obtained. A comparison of pulse-to-pulse correlation observed in the radar data with that predicted by a Monte Carlo simulation is used to obtain a measure of sea surface scatterer motion.

System to render constant the probability of false alarm in radar signals converted into numerical form

Abstract: Apparatus for obtaining constant false alarm probability in radar signals comprising a means to transform analog radar signals into digital signals with a quantity of binary numbers high enough to cause the density of probability of the amplitude of the digital radar signal to be maintained at a constant value.

Doppler radar sensor calibrator

Abstract: An electronic calibrator for doppler radar speed sensors and odometers comprising a variable impedance device, such as a varactor, positioned in the near-field of the radar antenna to modulate the radar probe beam, in the calibrate mode of the radar at a rate corresponding to the frequency of a doppler signal that would be sensed by the radar in its operating mode at a given speed. The impedance during the calibration mode is excited by a separate a.c. signal at a frequency corresponding to the doppler signal frequency. The output of the radar provides an indication during the calibration mode that can be adjusted to a calibrated indication corresponding to the actual speed causing a doppler signal of the same frequency as the excitation signal for the impedance.

Circuit arrangement for generating a sampling pulse raster adapted to the variable period of quasiperiodic events

Abstract: The invention is a circuit for generating a sampling pulse raster which has a pulse repetition frequency proportional to periodic events with variable period, which are to be sampled. The sampling pulses can be taken off at the counting stages of a pulse counter the counting input of which is connected to the output of a voltage-frequency converter. The voltage-frequency converter has two inputs: one for a voltage proportional to the period of the periodic events; another for a voltage proportional to the selected number of sampling pulses per period. The first voltage controls the frequency of the output pulses of the voltage-frequency converter in an inversely proportional sense.

Radar target direction simulator

Abstract: A system for accepting radar signals containing information simulating target range in time and amplitude, target velocity as a doppler, and target signature as an amplitude scintillation and adding target angular simulations of target space position and scintillations is described. An acousto-optic modulator is provided wherein a radar signal containing selected target simulations modulates an optical, infrared signal, in accordance with the selected target simulations. Beam steering mirror galvanometers are provided to selectively direct the modulated IR radiation onto selected areas of an RF (radar frequency) array. The mirror galvanometers in combination with selected areas of the RF array function to add target angular simulations and target space position and scintillations to the other simulations contained in the radar signal. The IR radiation is converted to a radar frequency signal in the RF array and is transmitted to the radar test system.

Non-interfering on-line receiver test system

Abstract: An on-line noise figure measurement system for receivers that produces va results whether or not signals are being received. A narrow pulse having a low pulse repetition frequency and low amplitude is injected into the receiver. A processing circuit cyclically measures the output of the RF stage of the receiver to produce a ratio of two signal values. One value is measured in the absence of any signal entering the receiver while the other value is measured with only the pulse signal impressed on the receiver.

Trichel pulse corona gas velocity instrument

Abstract: Velocity of a gas (e.g., wind) is determined as a function of the pulse repetition frequency of corona discharge (Trichel) pulses from a discharge probe positioned in the gas stream.

MTI performance enhancement device with instantaneous automatic gain control

Abstract: An instantaneous gain controlling system particularly for coherent (MTI) radar systems. A gain controllable intermediate frequency amplifier, a COHO, and a phase detector are shown along with an MTI canceller which itself includes a delay device and a differencer are shown. The delay device provides a full pulse repetition period of delay, and the differencer operates to subtract the coherent video at the phase detector output from the same signal train, one pulse repetition interval earlier, to provide MTI cancellation. The delayed video train is full wave rectified, passed through a threshold circuit and an adjustable gain video amplifier and used as a pulse-by-pulse gain controlling signal for the intermediate frequency amplifier. Large signal blocks are thus prevented from overloading the receiver channel with consequent spectral spreading and MTI cancellation degradation.

Pulsed doppler radar device having at least one range channel

Abstract: A pulsed Doppler radar device with variable repetition frequency, having at least one range channel operatively connectable at the pulse rate of the pulse repetition frequency, a doppler filter which suppresses clutter interference in the low Doppler frequency range, and a device for the variation of the pulse repetition frequency, in which the doppler filter of each range channel comprises at least one sampling-and-holding circuit and a following high pass or band pass filter, the switching pulse rate of the sampling-and-holding circuit being changeable with changes in the pulse repetition frequency, with the same high pass or band filter being utilized for all repetition frequency variations, the cut-off frequency of the following filter, if a high pass filter or, the lower cut-off frequency of such filter, if a band pass filter being approximately equal to the upper frequency of the clutter band width whereby the latter is suppressed, and the upper cut-off frequency, if a band pass filter is employed, being above the maximum pulse repetition frequency.

Electromagnetic radiation source locator

Abstract: A radiation locator apparatus includes a tuned or tunable radio receiver having an automatic gain control (AGC) circuit that provides a d.c. signal having an amplitude that is a function of the strength of the received radiation. A free running voltage controlled oscillator (VCO) is connected to earphones and produces a sound pitch that varies as a function of the magnitude of the d.c. (AGC) signal. An increase in the sound pitch may indicate an increase in the strength of the radiation received. When the locator is transported in a direction toward the source of radiation, the pitch increases thus guiding the operator to the source. The range of audible pitch may be extended by employing a pulse generator type of VCO since pulse repetition rates less than ten pulses per second are audible as spaced clicks that are equivalent to an extra low range of pitch.

Monitoring the sea surface with a short pulse radar

Abstract: A solution is presented for the scattering of short pulses from a stochastic, corrugated surface relative to the sea for the case of a narrow-beam transmitting antenna pointing near nadir. The spectrum of the received power and its time history are calculated and this solution is used to show that a measure of the variance of the surface ordinant can be obtained from the backscattered power. Included explicitly in the analysis is the finite nature of the source and the role of the small-scale wave structure (capillary wave range). It is shown that when sufficiently short pulses are transmitted, one can obtain a measure of the variance of the large scale surface ordinant from either the temporal spacing of the peaks in the returned power or from the envelope of the spectrum of the received power. Assuming an appropriate model for the statistics and spectrum of the surface ordinate, the variance can be used to compute the wind speed and the significant wave height of the surface.

A repetitively pulsed, Q-switched, inorganic liquid laser

Abstract: A circulating, inorganic liquid laser (Nd3+: POCl3/ZrCl4) delivering giant pulses in the 100 MW range was built. Repetition rates up to 10 pulses per second were achieved with very stable output properties after a warm-up time of a few minutes. The construction of the system and its performance are described in detail.

Application of a Lock-in Amplifier for Detecting Nanosecond Dye Laser Pulses

Abstract: The nitrogen-laser-pumped dye laser produces pulses of 2-8 nanoseconds in duration at repetition rates currently up to 500 pulses per second. With such a low duty cycle system, box-car analyzers are often used to amplify the signal from the photodetector. Except for some of the newer, ultra high-speed models, the box-car does not yield information as to pulse shape The technique to be described utilizes the more commonly available, and less expensive lock-in amplifier to measure light pulses. It will be shown that the signal derived with the lock-in is proportional to the total energy per pulse of the incident light. The technology employed to record oscillograms of these short duration pulses using regular side-on and end-on photomultiplier tubes is also discussed.

Microwave multiple-pulse breakdown in nitric oxide

Abstract: The minimum value of the peak RMS electric field for the TE11 mode resulting in the breakdown of pure nitric oxide has been measured in the pressure range 0·5-10 Torr. The microwave frequency was 9·361 GHz. For each pressure selected, the breakdown formation time τ was found as a function of the electric field. For all breakdown formation times, the minimum breakdown field occured at a pressure of 3-4 Torr, the pulse repetition frequency and pulse length being 100 pps and 4·7 ms respectively.

RADAR Pulse Expansion/Compression Filters Utilizing Surface Acoustic Waves

Abstract: Surface acoustic wave pulse expansion/compression filters have been developed at Hughes which have applications to modern RADAR systems. A review will be presented of two pertinent applications and the advantages of these devices will be emphasized.

Effects of errors in a binary multiplier on the accuracy of a closed-loop frequency meter

Abstract: The results show that the error due to pulse repetition frequency fluctuation in the feedback circuit does not exceed the weight of the least-significant digit, and it is dependent on the input frequency Fx and the conversion time-constant 2n/Fo. Therefore, if Fx is constant, the error of measurement has a definite sign and value, i.e., is static. This results in accumulation of error in subsequent mathematical processing of the code output, in particular integration.

Automatic frequency control for pulse radar and communication systems

Abstract: An automatic frequency control (AFC) system particularly suitable for pulse radar and communication systems with improved performance in that (a) negligible change in frequency occurs between pulses, assuring that the received signal remains centered in the receiver pass band during the entire receive period, (b) the center of the main lobe of the transmitter spectrum is used as the reference by gating out the rising and falling portions of the transmitter pulse where the frequency may be changing, and (c) the system cannot lock near the "image" frequency where the local oscillator is on the wrong side of the transmitter frequency and the receiver is mistuned.