Showing papers on "Phase noise published in 1981"

Time delay estimation using phase data

Abstract: The estimation of time delays between two received signals using phase measurements is discussed and the accuracy of such estimates is detailed. For the ideal case of statistically independent noise and no scattering at the receiver locations, it is shown that phase data regression lines yield time delay estimates with the same accuracy as other optimal time delay estimation procedures. For less ideal situations, the potential advantages of time delay estimation using phase data are discussed and illustrated. It is shown that regression analysis of phase estimates at properly selected frequencies can sometimes be employed to reduce bias errors in time delay estimates due to correlated receiver noise. It is also shown that the estimation errors due to scattering at the receiver location can often be assessed in nonparametric terms to provide time delay estimates with a realistic error bound.

Phase noise of single-mode diode lasers in interferometer systems

Abstract: Measurements have been made of the phase noise of six different types of single‐mode diode laser in an unbalanced Michelson interferometer, as a function of optical path difference. The frequency dependence of the phase noise has also been determined. Possible origins of the frequency fluctuations which result in the phase noise are discussed. The detrimental effect of the phase noise on the sensitivity and dynamic range of optical fiber interferometer sensors is briefly discussed.

On the signal-to-noise ratio and short-term stability of passive rubidium frequency standards

Abstract: Results are presented on theoretical calculations of the signal-to-noise ratio and of the short-term stability realizable in passive rubidium frequency standards. Measurements made on systems using either the separate hyperfine filter or the integrated hyperfine filter approach are reported. It is concluded that shot noise produced by the lamp at the photodetector is responsible for the observed white frequency noise spectrum limiting the stability in the short-term region.

Coherence limits for very-long-baseline interferometry

Abstract: The quality of the frequency standards used in very-long-baseline interferometry limits the coherent integration time and the accuracy of geodetic experiments except in special cases when clock instabilities can be made to cancel out by using differential interferometry. Formulas are derived for estimating the coherence of these interferometers from the Allan variances of the frequency standards. Experiments using extremely high-quality frequency standards, such as hydrogen masers, may be limited by the phase noise that results from atmospheric and ionospheric fluctuations.

Single-mode diode laser phase noise

Abstract: Measurements have been made of the phase noise of a single‐mode diode laser in an unbalanced Michelson interferometer, as a function of optical path difference. The noise increased linearly with increasing optical path difference. The origin of the phase noise is discussed.

Signal delay and waveform estimation using unwrapped phase averaging

Abstract: Detection and estimation under poor signal-to-noise conditions may require the averaging of an ensemble of time-locked measurements. However, when there is a variation in signal delay, it is necessary to adjust the alignment of the measurements in order for averaging to produce an undistorted estimate of the signal waveform. We describe a technique where alignment is, in effect, replaced by averaging the unwrapped Fourier phases of the measurements. The overall procedure yields an estimate of the signal at its mean delay. Simulations are presented to demonstrate the applicability of the technique to the estimation of delay in visual evoked potentials.

Quantum phase noise and linewidth of a semiconductor laser

Abstract: Quantum phase noise of a single longitudinal mode AlGaAs semiconductor laser is measured by converting it into intensity noise. A Michelson interferometer is used and a time delay is introduced. Results on spectral linewidth and noise spectrum are in good agreement with theoretical analyses based on a rate equation. Spectral linewidth of the semiconductor laser decreases from 100 MHz to 4 MHz in proportion to (I/Ith−1)−1 at the bias level of I/Ith=1.05 − 1.4.

Multimode fiber-optic hydrophone based on a schlieren technique

Abstract: A multimode fiber-optic hydrophone is described which is based upon a schlieren acoustooptic intensity modulation mechanism. Computer modeling of critical device parameters was experimentally verified and used to indicate ultimate attainable device performance. The device was shown to be able to detect the Knudsen noise level for frequencies up to 1 kHz, to have a dynamic range of 125 dB, to have an omnidirectional receiving response, and to be able to detect displacements as small as 3.4 × 10−3 A. The device is not susceptible to phase noise, is relatively insensitive to static pressure head variations and is electrically passive.

Performance and robustness trades in LQG regulator design

Abstract: The use of fictitious noise processes to improve the robustness of controllers based on linear quadratic Gaussian synthesis is studied in this paper. By constructing the noise process so that its effective energy is primarily in the frequency bands where robustness is lacking, improvements can be made without changing the closed-loop characteristics outside those frequency bands. Specifically, the use of fictitious colored input noise rather than white input noise, as in earlier studies, to improve control loop gain and phase margins, permits a more desirable trade-off between robustness and performance of the nominal plant.

Dynamic interferometry techniques for optical path length measurements

Abstract: Two dynamic interferometric techniques based on electrically tunable lasers are described and experimentally demonstrated. The first technique allows for measurements of small phase modulations in interferometers independently of dc drifts and low frequency noise in the interferometer. The second scheme is a true FM technique suited for continuous real-time noncontact measurements of the optical thickness of transparent materials.

Noise characteristics in line-narrowed semiconductor lasers with optical feedback

Abstract: Effects of optical-feedback-induced line-narrowing on low-frequency amplitude and phase noise of semiconductor lasers are reported. Free-running laser noise is compared with that of lasers operating with external mirror feedback. While less than 1 dB difference in the amplitude noise with and without feedback is observed, line-narrowed lasers exhibit 15?20 dB reduction in low-frequency wavelength instability, or phase noise.

Characterization of Frequency Fluctuations by Crosscorrelations and by Using Three or More Oscillators

Abstract: Summary The individual stability of an oscillator can be reached by using two auxiliary oscillators and comparing the three oscillators twotwo. The direct application of this principle gives erroneous results if the three comparisons are not made simultaneously. However the results are affected by the measurement system noises. New methods are proposed for comparing three oscillators. They use the concepts of crossvariance and crosscorrelation. They enable to characterize individually the oscillators and they reduce the influence of spurious noise sources, when uncorrelated. Therefore better resolution can be achieved in the frequency or phase fluctuation measurements.

Electronic phase-noise suppression in diode lasers

Abstract: It is shown that active current feedback reduces phase noise in diode lasers by between a factor of 1000 and 30 in the 0–250 Hz region.

The estimate of time delay between two signals with random relative phase shift

Abstract: This paper presents the maximum likelihood estimate of the time delay between two signals with random relative phase shift. The analysis applies for narrow-band signals and incorporates a parametric representation of the spread of the phase variation which allows the examination of all cases ranging from uniformly distributed phase shift to known phase shift. A realization of the ML estimator is presented which illustrates the difference between optimum processing for random phase shift and pure delay. The Cramer-Rao bound is also derived and the performance degradation with respect to the pure delay case is discussed.

Sensitivity of SAW Delay Lines and Resonators to Vibration

Abstract: One of the major advantages of SAW controlled oscillators is their very low level FR4 noise sidebands. However, in many applications where this low noise level is important, the oscillator must operate in an environment with high vibration levels. Evaluating the degradation of noise sidebands due to vibration is very difficult at this time since very little information exists in the literature. Therefore, a number of measurements on rotated Y-cut quartz SAW devices were made to determine the level of noise sidebands in a vibration environment. A number of different substrate-mounting techniques have been evaluated for both delay lines and resonators. The devices were vibrated in each of three perpendicular directions with both random and sinusoidal vibration used. The observed sensitivity to vibration varied by two orders of magnitude for different mounting geometries, with the lowest sensitivities being comparable to that of a well-designed AT-cut bulk wave resonator.

Acoustic noise suppression in the context of a perceptual model

Abstract: An acoustic noise suppression algorithm has been developed which suppresses noise from speech by first filtering it into a set of signals which approximate the loudness components perceived by the auditory system. These signals are generated by passing the input stimulus waveform through a filter bank with frequency bandwidths which approximate the ear's critical bandwidths. The noise on each signal is then suppressed using spectral subtraction techniques in a domain of simulated perception. This approach to noise suppression retains the intelligibility produced by spectral subtraction methods while eliminating the accompanying musical quality.

Error analysis of time delay estimation using a finite integration time correlator

Abstract: A methodology is presented for analyzing the error associated with time delay estimation using a finite integration time correlator, processing waveforms received at two separate sensors. The type of signal considered is a sinusoid whose amplitude is randomly modulated. The signals are assumed to be imbedded in additive Gaussian noise. Before they are correlated, the received waveforms are converted to a lower center frequency by mixers whose local oscillators are assumed to contain phase noise. By direct calculation in the time domain, the variance of the error in the time delay estimate is shown to be a function of integration time, signal-to-noise ratios, signal and noise bandwidths, and phase noise variance. The phase noise is shown to limit the accuracy of the time delay estimate. However, without phase noise, using the methodology the accuracy is shown to approach that obtained by the maximum likelihood estimator.

High-efficiency millimetre-wave silicon impatt oscillators

Abstract: High-efficiency impatt devices and oscillators have been fabricated from epitaxially grown silicon for operation in the frequency range 40?140 GHz. These devices have produced world state-of-the-art efficiencies and demonstrated the expected relative frequency insensitivity of silicon. Single drift devices have given efficiencies of approximately 8%; and double drift device efficiencies as high as 13.5% at 50 GHz and 12% at 90 GHz. Initial measurements show that the sideband phase noise levels follow a constant deviation law.

K-Band Tracking System for Domestic Satellite Communication System

Abstract: System design and operational results of a tracking system for a K-band Earth station antenna with a diameter of 11.5 m are discussed. Monopulse tracking technique using higher order waveguide modes is utilized. An investigation was conducted to clarify the rainfall effect and the effect of oscillator phase noise on the tracking receiver. An autotrack system is to be manufactured on the basis of these studies. Experiments were performed using the medium capacity communications satellite. No cross coupling was seen in the pull-in patterns. Sufficiently good results were obtained in tracking accuracy: less than 0.005° (peak value) under normal conditions, and less than 0.01° under an average wind velocity of more than 20 m/s.

Optical fibers for the distribution of frequency and timing references

Abstract: An optical fiber communications link was installed for the purpose of evaluating the applicability of optical fiber technology to the distribution of frequency and timing reference signals It incorporated a 15km length of optical fiber cable containing two multimode optical fibers The two fibers were welded together at one end of the cable to attain a path length of 3km Preliminary measurements made on this link, including Allan variance and power spectral density of phase noise are reported

Reduction of FM noise in impatt oscillators by optical illumination

Abstract: Experiments are described in which laser illumination of the active device has reduced the FM noise output by up to 5 dB for a GaAs impatt oscillator and 2 dB for a Si impatt oscillator. A qualitative explanation of the observed results is given, and the effect of laser amplitude noise on the maximum noise reduction obtainable is shown.

Tunable Magnetostatic Surface Wave Oscillator At 4 GHz

Abstract: An oscillator tunable from 1.8 GHz to 4.0 GHz has been fabricated using a Magnetostatic Surface Wave (MSSW) 2-port etched groove resonator as the frequency selective element, and a bipolar transistor amplifier for gain in the feedback loop. The theory for a resonator based oscillator is summarized, including the effect of loop gain, amplifier noise loop power, and resonator Q on oscillator noise. Noise and amplitude characteristics of the oscillator are reported over the tuning range. FM phase noise is comparable to YIG sphere oscillators and optimization should yield significant improvement.

Noise processing system for a television receiver

Abstract: A noise processing system is described for use in protecting a television receiver's sync processing path and its video processing path from impulse noise. To protect the video processing path, a first noise canceller receives a composite video signal, detects each noise pulse therein which exceeds a video noise threshold, and replaces each such noise pulse with a selected voltage level. The resultant noise processed video may then be applied to the receiver's video processing path. To protect the sync processing path, another noise canceller receives the composite video signal, detects noise pulses therein which exceed a sync noise threshold, generates a detection pulse for each such noise pulse, and combines the detection pulses with composite video so as to cancel the noise pulses. Thus, another noise processed video signal is developed for application to the receiver's sync processing path.

Synthetic multichannel time series for simulating underwater acoustic noise

Abstract: The paper discusses generation of synthetic multichannel digital time series based on measured directional and spectral characteristics (second-order statistics) of underwater acoustic noise. The data are intended for analyzing the performance of array signal processors. The noise is modelled as Gaussian, stationary and homogeneous. Second-order statistics are selected as representative of noise due to distant shipping, wind action and system self-noise. A multivariate autoregressive realization of the stochastic processes is obtained via the Levinson-Robinson solution of the normal Toeplitz equations. Implementation of the time series generator on an FPS AP 120B array processor is described.

SC-Cut Quartz Crystal Units in Low-Noise Oscillator Application at VHF

Abstract: SUMMARY Crystal-controll ed VHF oscillators are widely used in signal generators that must provide good short-term frequency stability and low phase noise. These oscillators utilize AT-cut crystals operating on an overtone mode. Further reduction of phase noise is difficult to achieve because of the amplitude-frequency effects exhibited by AT-cut crystal units. Doubly rotated crystals, such as SC-cut plates, exhibit significantly less amplitude-frequency effects than do AT cut. It, therefore, is feasible to operate the SC-cut crystal units at higher currents than are allowable in AT-cut crystal units. Provided that internal phase fluctuations associated with the oscillator do not increase significantly as crystal current is increased, improvement in short-term frequency stability and noise of the crystal-controll ed VHF signal generator is expected when using SC-cut crystal units. An examination of the practicality of obtaining lower noise oscillators at 100 MHz when using third overtone SC-cut crystals rather than fifth overtone AT-cut crystals was made. Measurement of the amplitude frequency dependence of the SC-cut and ATcut crystal units was made. The results indicate that crystal unit power dissipation can be increased 6- tolO-dB above levels that have been used with the AT-cut units. A review of noise sources associated with bipolar junction transistor oscillators indicates that second- and third-order distortion is responsible for the dominant flicker of phase exhibited in practical oscillators. The frequency correction term arising in solution of the vanderPo1 equation gives an insight into requirements for reducing flicker of frequency.