Showing papers on "Center frequency published in 1981"

An overview on the time delay estimate in active and passive systems for target localization

Abstract: Sonar and radar systems not only detect targets but also localize them. The process of localization involves bearing and range estimation. These objectives of bearing and range estimation can be accomplished actively or passively, depending on the situation. In active sonar or radar systems, a pulsed signal is transmitted to the target and the echo is received at the receiver. The range of the target is determined from the time delay obtained from the echo. In passive sonar systems, the target is detected from acoustic signals emitted by the target, and it is localized using time delays obtained from received signals at spacially separated points. Several authors have calculated the variance of the time delay estimate in the neighborhood of true time delays and have presented their results in terms of coherence function and signal and noise autospectra. Here we analyze these derivations and show that they are the same for the case of low signal-to-noise ratio (SNR). We also address a practical problem with a target-generated wide-band signal and present the Cramer-Rao lower bound on the variance of the time delay estimate as a function of commonly understood terms such as SNR, bandwidth, observation time, and center frequency of the band. The analysis shows that in the case of low SNR and when signal and noise autospectra are constants over the band or signal and noise autospectra fall off at the same rate, the minimum standard deviation of the time delay estimate varies inversely to the SNR, to the square root of the product of observation time and bandwidth, and to the center frequency (provided W^{2}/12 f\min{0}\max{2} \ll 1 , where W = bandwidth and f_{0} = center frequency of the band). The only difference in the case of a high SNR is that the standard deviation varies inversely to the square root of the SNR, and all other parameter relationships are the same. We also address the effects of different signal and noise autospectral slopes on the variance of the time delay estimate in passive localization.

Dual frequency anti-theft system

Abstract: An anti-theft tag (34) containing a semiconductor diode (36) connected to a metal antenna loop (38) is configured to receive two distinct radio frequency transmissions. The diode (36) bridges a closed loop at one end of the antenna (38), forming a tank circuit resonant at twice a selected center frequency. A first transmitter (26) generates a tone modulated radio frequency (f) displaced on one side of the center frequency, and a second transmitter (30) generates a continuous wave radio frequency (f) displaced on the other side of the center frequency. Both signals are fed separately to respective dipole radiating antenna strips (18, 19, 20, 21) on opposite sides of a surveillance area. The dipole strips for the different frequencies are at right angles to each other on each side; those for the same frequency are at right angles to each other on opposite sides. This produces cross polarized transmission of both frequencies within the area. Diode (36) of tag (34) mixes the two frequencies received by the antenna loop (38), causing the tank circuit to resonate at the sum of the two frequencies (double the center frequency). That resonant frequency is reradiated to receiver antennae (22, 24) on each side for detection by a very narrow band receiver (42) responsive to the sum frequency. The modulating tone is derived from the received signal and processed to trigger an alarm (44) when the detected signal is of sufficient strength and duration.

Bandpass filter for UHF band

Abstract: In a bandpass filter having five or more resonator stages, a sub transmission line is coupled to the main transmission line at the first and fourth resonators. The first to fourth resonators provide peak attenuation points at both sides of the center frequency in the attenuation curve, while the remaining resonators following the fourth resonator further sharpen the attenuation characteristics of the bandpass filter. The main and sub transmission lines may be formed by striplines on a printed circuit board, while the sub transmission line can be capacity coupled to the main transmission line. Coupling capacitances are freely set by setting the length of each gap between adjacent striplines to a desired value. Thus, the peak attenuation points can be accurately controlled to provide a bandpass filter having superior characteristics.

Millimeter Wavelength Frequency Multipliers

Abstract: Mechanically tuneable millimeter wavelength frequency doublers typically exhibiting 10-percent conversion efficiency at any output frequency in the range 100-260 GHz have been fabricated. Output power varies from 10 mW at 100 GHz to 6 mW at 260 GHz, with a fixed tuned instantaneous 1-dB bandwidth typically 5 percent of the center frequency. A frequency tripler to 215-GHz output frequency is also described. For this device, a mechanically tuneable 3-dB bandwidth of 210 to 240 GHz was obtained, with a peak conversion efficiency of 6 percent at 4.8-mW output power.

Noise reduction system having series connected low and high frequency emphasis and de-emphasis filters

Abstract: In a noise reduction system including a compressor and an expander having a complementary frequency response characteristic to the frequency response characteristic of the compressor, the compressor includes a high frequency emphasis variable frequency filter and a low frequency emphasis variable gain filter which are connected in a series circuit between input and output terminals and which respectively vary their parameters in response to the respective high and low frequency components of the compressor output. The expander includes a high frequency de-emphasis variable frequency filter and a low frequency de-emphasis variable gain filter which are connected in a series circuit between input and output terminals and which respectively vary their parameters in response to the respective high and low frequency components of the expander input.

Range measurement by means of frequency modulated continuous wave radar

Abstract: A continuous wave FM range measuring apparatus for transmitting a signal F which is linearly modulated by a sawtooth signal over a frequency excursion ΔF during a duration T and which has a central frequency f1. A phase loop is provided for stabilizing ΔF and f1 with the precision of a quartz oscillator. A mixer produces a beat signal fb between the transmitted signal F and a received signal F' reflected from an object. The frequency fb and the phase φbo of Fb at the beginning of the sawtooth ramp are measured. The distance is calculated, preferably by means of a microprocessor (10), by first calculating an approximate value d1 of the distance d to be determined between the radar and the object as a function of ΔF, fb and T. Then a more precise second value d2 of d is calculated from d1, φbo and the value fo of F at the beginning of the ramp. In a preferred embodiment, the level of a liquid in a container is measured.

Methods, and apparatus, for transmitting high-bit-rate digital data in power line communication media having high harmonic noise content

Abstract: In a power line data communications system, high-bit-rate digital data is transmitted through a communications media, having high harmonic noise content, by use of a frequency-modulated chirp waveform. The chirp waveform instantaneous frequency is at a predetermined center frequency at the start, midpoint and end of each bit time interval, and makes substantially linear frequency changes to a maximum frequency and a minimum frequency at selected ones of the one-quarter and three-quarter bit-time-interval times. A binary-one data bit is transmitted by increasing the instantaneous frequency to reach the maximum frequency at the one-quarter interval time, then decreasing the frequency to reach a minimum frequency at the three-quarter interval time, and reducing the instantaneous frequency thereafter to reach the center frequency at the end of the bit time interval. A binary-zero data bit is transmitted by initially decreasing the instantaneous frequency to reach the minimum frequency at the one-quarter interval time, then increasing the instantaneous frequency to reach the maximum frequency at the three-quarter interval time, and reducing the instantaneous frequency thereafter to reach the center frequency at the end of the bit time interval. One presently preferred embodiment of apparatus for transmitting the chirp frequency-modulation signal, and one presently preferred embodiment of apparatus for receiving the chirp frequency-modulated waveform for recovering the data modulated thereon, and associate timing information, are disclosed.

High-sensitivity fm signal demodulation system.

Abstract: The present invention relates to the improved demodulation system which improves the noise characteristics for the demodulation of a wideband television FM signal. A variable bandpass filter (8), the center frequency and the bandwidth of which are controllable, for improving C/N, is inserted at the output of a reference bandpass filter (7) in an FM signal path. The bandwidth of the variable bandpass filter (8) is controlled so that said bandwidth is wide when the input carrier level is high, and said bandwidth is narrow when the input carrier level is low. The center frequency of the variable bandwidth filter (8) is controlled so that said center frequency follows to the instantaneous frequency of the color sub-carrier component (3.58 MHz). Said color sub-carrier component is derived by a narrow-band bandpass filter (10) coupled with the output of said discriminator (9) for controlling the center frequency of the variable bandpass filter (8).

Computer-Optimized Design of Quarter-Wave Acoustic Matching and Electrical Matching Networks for Acoustic Transducers

Abstract: An iterative computer program was developed to optimize the parameters for the acoustic matching layer(s) and the electrical matching network of a transducer for a minimum length of the impulse response. By including the interactions between electrical and acoustic matching in the authors' model, the quality of the transducers has been significantly improved. A 3.65 MHz center frequency transducer, made of Murata PZT, was constructed to verify the computer results. The impulse response was approximately 2-1/2 cycles long with a round trip insertion loss of 10.9 dB at the center frequency, and the 40 dB ringdown time was 1.5 ..mu..sec when working into a water load.

Optical analyzing instrument with equal wavelength increment indexing

Abstract: In an instrument adapted particularly for analyzing agricultural products, such as grain, interference filters are rotated successively through an infrared wide wavelength band beam of light, which irradiates a sample of the product. Each of the interference filters operates to transmit a narrow wavelength band of light, the center frequency of which is scanned through a range of values as the angle of incidence of the beam of light to the interference filter varies as the filter rotates through the beam of light. An optical track is provided which rotates with the assembly of interference filters to generate pulses from index markings in the optical track. The markings in the optical track are spaced so that one pulse is generated for each angstrom of variation of the center frequency transmitted through an interference filter. The pulses are counted in the counter and the counts in the counter are used to control the selection of intensities reflected from the sample to be used in the analysis of the sample.

Electronic musical instrument of a formant synthesis type

Abstract: A musical tone is synthesized by frequency modulation which realizes a desired fixed formant. A first accumulator repeatedly adds a constant corresponding to a center frequency of the fixed formant at a regular time interval to generate phase angle data of a carrier. A second accumulator repeatedly adds a constant corresponding to a fundamental frequency of a selected note at a regular time interval to output a carry out signal each time the accumulated value has exceeded a predetermined modulo number. By resetting the first accumulator repeatedly by this carry out signal, the phase angle data of the carrier is brought into a harmonic relation with the fundamental frequency. By effecting frequency modulation using this phase angle data of the carrier and the fundamental or harmonic frequency of a selected note, a musical tone in which harmonic components of the selected note are controlled in accordance with the desired fixed formant is synthesized. A third accumulator repeatedly adds a constant corresponding to a modulating frequency peculiar to the desired fixed formant at a regular time interval. Contents of the third accumulator are repeatedly reset by a carry out signal from the second accumulator. As a result, the output of the third accumulator is brought into a harmonic relation with the selected note and therefore is suitable for use as phase angle data of a modulating frequency in the frequency modulation.

Time delay estimates in passive sonar target localization

Abstract: In passive sonar systems, a target is localized using time delays obtained from signals received at spatially separated points. The variance of the time delay estimates about the true time delay at low signal‐to‐noise ratio (SNR) depends on SNR, bandwidth, center frequency, and spectral slopes of signal and noise. The accuracy of time delay estimation can be enhanced using a pre‐shaping filter. We shall show in this paper that if signal and noise spectral fall off rates are close to each other (within 3 dB/oct), then the preshaping filter does not appreciably enhance the accuracy of time delay estimation. However, if the signal and noise spectral slopes are significantly different (about 6 dB/oct), then the preshaping filter increases the accuracy.

FM Demodulator with variable bandpass filter

Abstract: The demodulator combines a conventional frequency discriminator with a bandpass filter for removing the noise which is present from the band occupied at a given instant by the modulated signal. The center frequency of the bandpass filter is controlled in dependence on the instantaneous frequency of the modulated signal and its bandwidth bu is controlled in dependence on the instantaneous width of the band occupied by the modulated signal.

Microwave test apparatus and method

Abstract: A method and apparatus for monitoring the resonant frequency and absorption level at resonance of an absorption type resonant cavity which involves providing a voltage controlled oscillator, applying to the control input of the voltage controlled oscillator a control signal having a main component V m and a dither component V d , splitting the output signal from the voltage controlled oscillator into a portion directed along a test path and a portion directed along a reference path, the reference path including an attenuator controlled by a voltage signal V k , directing the signal in the test path through the resonant cavity, splitting the signal emerging from the resonant cavity into a portion directed along a frequency detection path and a portion directed along a level detecting path, using the signal directed along the frequency detection path for generating a signal for changing the amplitude of V m until the center frequency of the output signal of the voltage controlled oscillator is at the resonant frequency f r of the cavity, and using the signal directed along the level detection path for changing V k until the level of the signal in the reference path is equal to the depth of the null of the signal in the level detection path.

Apparatus for acquiring and collecting radio signals coming from a plurality of stations

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

Variable Bandpass Filters Using Varactor Diodes

Abstract: A rectangular waveguide type variable bandpass filter for the 4-GHz bandpass has been proposed and tested. The bandpass width varies from 260 MHz to 1.02 GHz for a filter using varactor diodes. Two microstrip variable bandpass filters for the 6-GHz and 4-GHz bands are also proposed and tested. The passband width varies from 310 MHz to1.24 GHz for a varactor-diode coupled filter, and it varies from 380 MHz to 2.18 GHz for a filter which is composed of low-pass and high pass filters connected in cascade. The center frequency of the three filters can be changed arbitrarily.

Measurement of Ultrasound Attenuation in Tissues from Scattered Reflections: In-Vitro Assessment of Applicability

Abstract: The attenuation of ultrasound may become a useful parameter in in-vivo tissue characterization. A simple approach using the video signal of A-mode equipment and decompressing the amplitude levels has proven to yield significant information (cf. Thijssen et al. 1980, 1981). Since the A-mode signal contains only disturbed frequency information a better signal for studying the frequency dependence of tissue interaction is of course the radio frequency (RF) echogram. Two parameters may be derived then, i.e. the attenuation per centimeter tissue at a particular frequency (e.g. the center frequency of the transducer), and the frequency dependence of the interaction of ultrasound with tissue expressed by the spectral slope, i.e. the spectral power relative to some internal (i.e. another tissue sample) or external reference power spectrum. The attenuation and the frequency dependence can by summarized by the so-called tissue transfer function, or tissue impulse response (Kak & Dines 1978, Dines & Kak 1979).

Ultrasonic pulse-echo beam width and axial response approximations for clinical broadband focused transducers.

Abstract: A means of estimating the pulse-echo response beam width and the position of the peak: in the pulse-echo axial response for clinical ultrasonic transducers is presented. Using a simple model based on continuous wave propagation, equations describing the width of a transmitted beam and the axial pressure amplitude as a function of distance from the transducer have been adapted to describe broadband transducers. The efficacy of these adaptations is verified by comparison to actual measurements performed on both focused and non-focused transducers for attenuating paths as well as “lossless” water paths. By using either the center frequency or a computed mean frequency to represent a broadband pulse, both the −20 dB pulse-echo response beam width and the divergence of the beam as it propagates through tissue-like material can be well approximated. Also, for nonattenuating paths, the position of the peak in the axial pressure profile, and, hence, the focal plane position, can be estimated from the phys ical dimensions of the focused transducer and the center or mean frequency.

Passive CCD resonator filters

Abstract: Novel passive recursive CCD bandpass filters have been realized using standard two-level-polysilicon gate NMOS technology. A Chebyshev bandpass (w/SUB rel,/ /SUB 3/ /SUB dB/=3.1 percent) and a fully integrated CCD signal filter with an extremely narrow 3 dB bandwidth of 97 Hz (Q=1350) at 131.85 kHz center frequency were implemented by means of cascaded CCD resonators. The latter chip contains the necessary clock generation and biasing circuitry realized with dynamic circuit techniques to achieve low power consumption (40 mW per filter). Performing all filtering operations exclusively in the charge domain ensures filter passivity. An extremely stable center frequency and a bandwidth independently controlled by a capacitance ratio are the special advantages of such filters.

Electronic musical instrument of fixed formant synthesis type

Abstract: A musical tone is synthesized by controlling harmonic components of a note selected in a keyboard in accordance with a desired fixed formant. A parameter computation circuit detects a harmonic frequency which is nearest to a center frequency of the fixed formant and produces FM computation parameters using the nearest harmonic frequency as a carrier frequency and a fundamental or harmonic frequency of the selected note as a modulating frequency. A frequency modulation circuit performs an FM computation on the basis of these parameters and, as a result, a tone whose harmonic components have been controlled in accordance with a formant having the nearest harmonic frequency as a central component is synthesized. The parameter computation circuit computes frequency difference between the nearest harmonic frequency and the center frequency of the fixed formant for controlling the level of a formant synthesized in a frequency modulation circuit in accordance with this frequency difference. This level control is achieved by controlling an amplitude coefficient of a tone or a modulation index in the FM computation. A subformant having as its central component another harmonic frequency in the vicinity of the nearest harmonic frequency may be formed in a relatively low level for reinforcing the formant with this subformant.

Wide-Band Signal Processing Using the Two-Beam Surface Acoustic Wave Acoustooptic Time Integrating Correlator

Abstract: A new acoustooptic architecture for performing real-time correlation of high-frequency wide-band signals has been developed. It uses a surface-acoustic-wave (SAW) delay line, and features the optical interference of two coherent light beams which have been Bragg-diffracted by SAW's propagating in the line. The signal multiplication, and subsequent time integration of the product formed, is performed by a photodiode array which detects the diffracted light. This architecture has achieved time-bandwidths products exceeding 10/sup 6/ (34 MHz X 30 ms), and has several attributes which make it particularly well suited for use as a spread-spectrum signal processor. These include linearity of operation, large dynamic range, a large time aperture over which the correlation can be observed, and the ability to determine the center frequency and bandwidth of the signals. A correlator with this architecture has been used to detect a number of wide-band spread-spectrum signals. Its suitability for use as a signal processor in several spread-spectrum systems is considered.

Monolithic GaAs Lange coupler at X-band

Abstract: Monolithic 3-dB Lange couplers have been fabricated on semi-insulating GaAs. Loss at the center frequency of 9.5 GHz is 0.7 dB.

Stepped-Ferrite Tunable Evanescent Filters

Abstract: A new technique is described for the design of magnetically tunable filters. With this approach, the resonant sections tune at the same rate enabling maintenance of response shape as center frequency is varied. The filters are minimum-phase structures, realizable with as many poles as required. The design is capable of handling much greater power than single-crystal YIG designs, although the tuning bandwidth is much less.

Direct analysis of time-varying continuous and discrete difference equations with application to nonuniformly switched-capacitor circuits

Abstract: The exact time-varying transfer functions of circuits or systems described by matrix continuous difference equations and discrete difference equations are obtained. The method is a time-domain analysis without nsing any transform technique and the familiar s, z and nonuniform fraction of z variables are introduced in the process of analyss. The transfer functions at Input signal frequency and harmonic frequencies are given explicitly In closed forms. Criteria for stability and asymptotic stability In the sense of Lyapunov are given. Well-known examples of switched-capacitor (SC) circuits are discussed, and new insights are given. A general SC N-path circuit structure is proposed and its time-varying transfer function is obtained. An example of 3-path circuit is given as an illustration to show that its frequency characteristics such as center frequency and Q are well defined by its switching frequency and a capacitor ratio.

Noise signal generator

Abstract: PURPOSE:To generate a noise signal that has a center frequency and frequency spectrum with prescribed precision, by performing prescribed modulation and amplification of a received signal by use of a serrodyne traveling-wave amplifier tube. CONSTITUTION:To the helical electrode of serrodyne traveling-wave amplifier tube 13, a saw-tooth signal from saw-tooth oscillator 14 and a white noise, bandlimited by low-pass filter 16, from while-noise generator 15 are applied being superposed mutually by adder 17 and a received signal to be amplified by serrodyne travelingwave amplifier tube 13 in phase-modulated. Then, serrodyne traveling-wave amplifier 13 tube outputs a noise FM signal that has its center frequency shifted from the frequency of the received signal by the extent corresponding to the differential value of the saw-tooth signal and shows an electric spectrum whose electric power half-value width is distributed in a gauss shaped proportional to the electric power spectrum width of the while noise.

Interferometric surface-wave acousto-optic time-integrating correlators

Abstract: A structure for a coherent-interferometric acousto-optic (AO) time-integrating correlator was implemented by using a single surface acoustic wave (SAW) device with tilted transducers to reduce intermodulation terms. The SAW device was fabricated on Y-Z LiNbO3 with a center frequency of 175 MHz, a bandwidth of 60 MHz, and a time aperture of about 10 micros. The density of the photodetector array, with a potential of 120 MHz. Typical integration times are 30 to 40 ms, providing processing gains in excess of 10 to the 6th power. Such a device is useful in providing fast synchronization of communication links and in demodulating to base band and simultaneously acting as a synchronization lock monitor for moderate data rates. Where processing may be limited by Doppler shifts, a two dimensional architecture was implemented to allow full processing gain. Two one-dimensional, SAW AO time-integrating correlators and a two dimensional correlator are evaluated.

Digital type phase lock loop circuit

Abstract: PURPOSE:To get rid of the phase error information, by setting the discrete value of the dividing rate (n) or an output of the variable frequency oscillator for oscillating the frequency of ''n'' times of an input signal, to the register by means of an input pulse, and controlling the oscillator by making this set value an analog value. CONSTITUTION:An output signal 5 of the variable frequency oscillator 4 of the center frequency which is ''n'' times as much as the nominal frequency (f) of an input data signal 1 is input to the latch circuit 3 and the counter 10 of dividing rate (n). The input signal 1 is provided to the latch circuit 3, is latched by an output of the oscillator 4, this latched output is provided to the store register 9, and the contents of the counter 9 at that time are stored. An output signal 14 of the store register 9 displays a phase error by a digital value, and it is provided to the D/A 15 converter. An output which displays a phase error of the D/A converter 15 by an analog value is provided to the variable frequency oscillator 4 through the filter 17, and its output becomes the frequency of (n) times exactly, whose phase has been corrected by an input signal.

Frequency monitor with adjustable tolerance

Abstract: There is disclosed a frequency monitor circuit, for monitoring AC power frequency for example, in which a gate is provided for a stable oscillator and frequency divider circuit which is responsive to the frequency divided monitored signal and a flip-flop circuit to produce a fixed reference period signal equal to a predetermined number of cycles of the oscillator commencing at the beginning of a full cycle of the monitored signal; a two-stage timer which determines the tolerance for the monitored signal frequency and is adjustable is provided with signals from the monitored signal divider circuit and the fixed reference period circuit and arranged so that the end of the reference period or the end of the divided monitored signal cycle, whichever occurs first, will start the timer. Its output latches a pair of flip-flop circuits acting as decoders which are respectively supplied with the state of the frequency divided monitored signal and the fixed reference period signal. If both have ended and changed state, the monitored signal is determined to be within frequency tolerance; if the frequency divided monitored signal has not changed state the frequency is low; if the fixed reference period signal has not changed state the frequency is high; high and low indicators are provided and a relay driver is operated in response to a within-tolerance condition. A double frequency detector circuit produces an inhibiting signal which resets the low frequency decoder flip-flop and prevents a false low frequency signal for monitored signal frequencies about or more than double the center frequency. One stage of the two stage timer is caused to have a negligible time delay by a signal fed from the out-of-tolerance output of the decoder circuits so that entry into within tolerance condition is more restricted than maintenance of within tolerance condition thus preventing vacillation between the two conditions in borderline cases.

Linearized FM quadrature detector

Abstract: In an FM receiver a multiplier is driven from the IF limiter. The limiter also drives a single tuned circuit which produces a quadrature signal that drives a second port in the multiplier. When the quadrature signal is multiplied by the IF signal an FM detector results. The center frequency is determined by the frequency of the quadrature relationship and the extent of the resultant output curve is determined by the Q of the tuned circuit. The output response is linearized by varying the current in the multiplier as a function of the IF signal deviation.