Showing papers on "Bandwidth (signal processing) published in 1970"

Experimental Confirmation of an HF Channel Model

Abstract: Specially designed HF ionospheric propagation measurements were made and analyzed to confirm the validity and bandwidth limitations of a proposed stationary HF ionospheric channel model. In the model, the input (transmitted) signal feeds an ideal delay line and is delivered at several taps with adjustable delays, one for each resolvable ionospheric modal component. Each delayed signal is modulated in amplitude and phase by a baseband tap-gain function, and the delayed and modulated signals are summed (with additive noise) to form the output (received) signal. Statistical specifications for the tap-gain functions involved three hypotheses: 1) that each tap-gain function is a complexGaussian process that produces Rayleigh fading, 2) that the tapgain functions are independent, and 3) that each tap-gain function has a spectrum that in general is the sum of two Gaussian functions of frequency, one for each magnetoionic component. Statistical tests were performed on daytime and nighttime measurements confirming the validity of the three hypotheses, and thereby the validity of the model. For practical applications, the model can be considered valid over a bandwidth equal to about one fourth of the reciprocal of the effective (weighted) time spreads on the ionospheric modal components. The model should be useful both in theoretical analyses of communication system performance and for channel simulator designs.

Very Long Baseline Interferometry with Large Effective Bandwidth for Phase‐Delay Measurements

Abstract: The degree of delay-measurement precision that is achievable by very long baseline interferometry depends on the effective bandwidth of the recorded signals. Methods of extending the effective recorded bandwidth for a fixed tape-recorder bandwidth are examined in theory. Two major schemes (simultaneous recording of many widely separated frequency channels and recording sequentially different frequency channels) are examined in detail. Other techniques which involve rapid sampling and temporary ‘buffering’ of data bits are discussed. Methods of processing the data to achieve the maximum-likelihood estimates of phase delay, fringe phase, and fringe rate are derived. Factors that determine the optimum choice of frequency channels are discussed by using a delay ‘resolution or ambiguity’ function. This function is analogous to the beam-pattern function of a one-dimensional antenna array. Theoretical signal-to-noise ratios for the delay and fringe phase measurements are derived by using a simple vector representation of the signal and noise.

Very High-Q I nsensitive Active RC Networks

Abstract: Abstracf-A new circuit realizing high stable Q’s is presented. The frequency dependence of the operational amplifiers, which has been the principal limiting factor for high & at higher frequencies for networks presented in the literature, has been taken into account. The performance of the new network is shown to be superior to the realizations thus far presented in the literature for the following reasons. The Q realized by the new circuit is independent of the operational-amplifier bandwidth, which results in a stable response. The realization is also insensitive to manufacturing tolerances and, therefore, it can be readily tuned for the desired & and center frequency without encountering any stability problems. I. INTRODUCTION HE ADVENT of integrated-circuit (IC) technology has caused significant change in the philosophy of network design. In particular, where improvement in network performance and/or reliability can be achieved, it is now practical .to use more than one active element. Also, at low frequencies and narrow bandwidths, where inductors are physically large and expensive, the use of inductorless networks is desirable, and often a necessity. This paper is, therefore, concerned with the realization of very high Q, where Q = w,,/w~~~, responses with active RC networks.

Carrier Transmission of Binary Data in a Restricted Band

Abstract: The spectra of digital frequency modulation (FM) signals have been observed to be narrow compared with the spectra of digital baseband signals or the corresponding amplitude modulation (AM) and phase modulation (PM) signals. This suggests a high efficiency of transmission in terms of occupied bandwidth for binary FM. Here the desirability of digital FM systems is investigated further with an examination of the probability of bit error. The FM receiver considered consists of a predetection filter, a limiter-discriminator, and a postdetection filter. New results are presented on the effect of predetection bandwidth restriction on the error performance of binary FM systems for various frequency deviations. Theoretical results have been obtained by a Fourier analysis of the distorted FM signals and by Rice's click analysis of FM noise. The data presented permits an optimum selection of system parameters such as frequency deviation ratio and predetection filter bandwidth. It is found that in narrow-band operation a peak-to-peak frequency deviation of about 0.7 times the bit rate and a bandpass filter bandwidth of about 1.0 times the bit rate yield a minimum probability of error. Experimental measurements have been made and there is, in general, good agreement with the theory. A comparison of the error performance of noncoherent binary FM, coherent AM, and coherent PM in a restricted band is made. Narrow-band noncoherent FM proves superior to AM in any bandwidth. In narrow-band operation, the noncoherent FM gives a somewhat better error performance than the coherent PM. For example, for an error rate of 10-4and a bandpass filter bandwidth of one times the bit rate, the performance of a noncoherent FM system is 0.7 dB better than that of a coherent PM system.

Wide-band optical communication systems: Part II—Frequency-division multiplexing

Abstract: Frequency-division multiplexing techniques offer means for circumventing the bandwidth limitations of optical modulators and detector. Practical broad-band long-distance optical communication system of this type appear feasible and some possible embodiments are described. Calculations are made to determine the approximate information capacity and other characteristics of several 4000-mile repeaterad systems.

Digital Transition Tracking Symbol Synchronizer for LOW SNR Coded Systems

Abstract: In coded telemetry systems symbol synchronization must be performed at low symbol signal-to-noise ratios ( ST/N_{0} ) with negligible degradation from the perfect synchronization case. A digital transition tracking synchronizer which operates with less than 0.03-dB degradation at ST/N_{0} = -3 dB and at rates of 5.6 bit/s to 250 kbit/s is described.

Adaptive Equalizer for Pulse Transmission

Abstract: Results are reported which are of interest in the automatic adaptive equalization of telephone lines or other narrowbandwidth channels where data transmission is limited primarily by intersymbol interference. We describe an algorithm for adjusting the tap gains of a tapped delay line (TDL) equalizer which converges for all channels to the setting, which minimizes the mean-square error (rose) at the filter output due to both noise and intersymbol interference. This algorithm has been implemented using digital microcircuits and metal-oxide semiconductor (MOS) shift registers to construct a 63 tap all-digital TDL filter covering 19.7 ms. The modulation system used is vestigal sideband with bandwidth 1.6 kHz. The data rate is 3200 pulses/s, or 9600 bit/s with 8 data levels. A description of the hardware realization and performance data over various telephone lines is given.

Some Design Considerations and Realizations of Iris-Coupled YIG-Tuned Filters in the 12-40 GHz Region

Abstract: YIG filters covering the frequency ranges 12 to 18, 18 to 26, and 26 to 40 GHz have been designed and developed. The filters in the 18- to 40-GHz range were of three sections and achieved 80-MHz bandwidth and greater than 40 dB of higher order mode rejection. The filter in the 12- to 18-GHz region was of four sections utilizing staggered spheres in order to achieve a larger bandwidth filter with a minimum magnet gap. The bandwidth of this filter was 50 to 60 MHz with greater than 55 dB of higher order mode rejection. Useful information for the design of these filters was obtained with a special test fixture built to measure mutual coupling between spheres as a function of the angle between the line joining the sphere centers and the dc magnetic field. This data is reported for various iris sizes, shapes, and sphere spacings and indicates large differences in mutual coupling as the angle is varied from 0 to 90/spl deg/. The effect of various types of discontinuities and iris sizes and shapes on higher order mode excitation and coupling are discussed as well as constructional problems and the design of high field magnets from vanadium permendur.

Data transferring system utilizing a monitor channel and logic circuitry to assure secure data communication

Abstract: The transmitter-encoder of the data transferring system utilizes polybinary, correlative encoding to develop an information carrying signal, which includes a monitor signal having a known data code, and data from a plurality of sources. The encoding techniques facilitates redundant bit transmission in a constrained bandwidth. The receiver-decoder includes monitor channel logic circuitry which determines whether the decoded signal is free from error. Moreover, each of the data decoding channels utilizes majority logic to verify that a particular control initiating signal is being received before the control signal is applied to data utilization devices associated therewith. If one error is detected in the monitor signal, the data channels are squelched for a first predetermined period of time thus preventing erroneous control signals from being applied to the utilization devices. If more than one error is detected in the monitor signal within a second predetermined period of time the data channels are squelched for a third predetermined period of time and an alarm is activated by the monitor channel-logic circuitry. As a result, the system provides security against abnormal transmission characteristics.

Recording and reproducing system for color video signal

Abstract: In recording a composite color video signal consisting of a luminance signal and a modulated chrominance signal having its frequency band contained within the luminance signal band, a carrier is frequency modulated with the luminance signal separated from the composite signal, the modulated chrominance signal separated from the composite original is frequency converted to have a frequency band juxtaposed to the lower limit of the bandwidth of the frequency-modulated luminance signal, and the latter is combined with the thus converted chrominance signal and with a pilot signal having a still lower bandwidth to provide a combined signal which is magnetically recorded. Upon magnetic reproduction of the combined signal thus recorded, the pilot signal, frequency-modulated luminance signal and converted chrominance signal are separately extracted from the reproduced signal, amplitude variations of the pilot signal are detected to control the amplitude of the converted chrominance signal which is reconverted to substantially its original frequency band by reference to the pilot signal, and the frequency-modulated luminance signal is demodulated and combined with the reconverted modulated chrominance signal to provide the composite color video signal.

Digital signal synchronizing system

Abstract: A digital signal synchronizing system wherein a locally generated timing signal is compared with received binary data. If the timing signal lags the bit rate of the binary data, pulses are added to the timing signal and if the timing signal leads the binary data, pulses are deleted from the timing signal. Means are provided for controlling the bandwidth of the system and the system, in addition, has a phase versus frequency response which is substantially constant over the range of operating frequencies.

Noise Bandwidth of Common Filters

Abstract: The noise bandwidth B N of Butterworth, Bessel, and Chebyshev filters is tabulated. The Butterworth filter is shown to have the minimum B N to 3-dB bandwidth ratio for any secondorder filter. It is proven that B N is invariant when a low-pass to bandpass transformation is made. An error is corrected in recent tables of Chebyshev filters.

A computer simulation study of real-zero interpolation

Abstract: The technique of real-zero interpolation (RZI), first described by Voelcker, permits the interpolation of a minimum-bandwidth waveform to a set of zero crossings on the time axis. RZI can thus lead to bandwidth compression of intrinsically 2-level signals, or to the conversion of analog signals into a type that is impervious to instantaneous non-linear distortion. The purpose of the simulation study described was to examine how RZI performs in a realistic communication environment, i.e., when the transmission channel is noisy, has a finite dynamic range, and when zeros can occur only at discrete points on the time axis. Attention is focused on 2-level facsimile as the most likely candidate for RZI processing, but other types of signal such as synchronous data and synchronous pulse-width modulated waves have also been studied. It is shown that RZI can yield substantial bandwidth saving for signals that carry information by their zero crossings only. The price is paid in increased vulnerability to channel noise; this may limit the applicability of RZI to channels with over 35 to 40 dB signal-to-noise ratio. Excessive amplitude swings, intrinsic to the system, can be controlled by the insertion of complex zeros. RZI may lead to a bandwidth saving of the order of 6:1 for 2-level facsimile signals. Its data handling performance is characterized by the measured rate of 1.0 to 1.6 bit/Hz. An application to direct analog encrypting of speech signals by multiplicative distortion is also described.

Frequency spectrum analyzer with fft computer

Abstract: A broad band of signal frequencies, whose power spectrum is to be analyzed by the Fast Fourier Transform (FFT) technique, is sampled by heterodyning with various beat frequencies fb and passage of the modulation products through a low-pass filter of bandwidth b/2 where b represents the width of a subband substantially narrower than the overall band of width B. By concurrently performing the heterodyning operation in two parallel channels, with introduction of a 90 DEG phase shift between beat and input frequencies in one of the channels, the two sidebands fb +fx and fb -fx (where fx represents any frequency within the selected subband b) can be separated in the outputs of the two channel filters. Frequency limit b/2 is selected in conformity with the capacity of an associated computer to handle the data from the FFT analysis of the subband spectrum. The sampling may be preceded by a transposition of the entire band B to a higher frequency range, in order to prevent any possible cluttering of the spectrum by harmonics of fb .

Rf rejection filter

Abstract: An RF suppression filter using several quarter RF wavelength long strips in parallel that are open-ended to form an RF ground at their common tie-points in the form of a section of conductive line. This base line is extended to terminations at each end to a length beyond the respective outside stubs that enables all stubs to recognize the same electrical reference plane and yet to a length that is short relative to any RF wavelength encountered within the operational bandwidth for the filter.

Microwave Filters of Coupled Lines and Lumped Capacitances (Correspondence)

Abstract: Two frequency transformations are given which enable microwave filters to be realized with coupled lines and lumped capacitances from a characteristic prototype lumped network to a good approximation. The procedore includes filters originally proposed by Matthaei and CristaI, and enables realizations for large bandwidths. A number of examples demonstrate the efficiency of the procedures.

Performance Analysis of DSSS and FHSS Techniques over AWGNChannel

Abstract: With the ever-growing advancements in the field of technology, Digital communication systems are becoming increasingly attractive and flexible for a secure form of data communication. Spread Spectrum overcomes the severe levels of interference that are encountered in the transmission of the digital information and rely upon shift register codes. This paper is in accordance with the design of Spread Spectrum techniques, namely Direct Sequence Spread Spectrum (DSSS) and Frequency Hopped Spread Spectrum (FHSS) which involve spreading the bandwidth of the signal to minimize the troubles that can arise from the vulnerabilities of conventional circuits, through channel. This paper further elaborates about the performance analysis of the above techniques which includes Signal-to-Noise(S/N) ratio and transmitted power parameters, when the transmitted signal is corrupted by Additive White Gaussian Noise (AWGN).

Automatic transversal equalizer

Abstract: An equalizing circuit, intended to be inserted between the transmission link and the receiver of an electrical information transmission system, the equalizer being arranged to have, within a preselected bandwidth of audio frequencies, an amplitude frequency response in the form of a family of similar curves, the equalizer including comparison means which is responsive to the difference between the outputs of the equalizer at two different frequencies of which at least one is within the said bandwidth to thereby automatically select a predetermined one of the said curves.

A Latching Ring-And-Post Ferrite Waveguide Circulator

Abstract: This paper presents the performance and normalized design parameters for a latching ring-and-post ferrite circulator in waveguide. A C-band circulator has provided an insertion loss of 0.35 dB and a 20-dB isolation bandwidth of 17 percent. When the circulator was matched for higher maximum isolation (50 dB) but narrower bandwidth (10 percent) at room temperature, the 20-dB isolation bandwidth was 7.8 percent across the -40/spl deg/ to +75/spl deg/C temperature range. Low-loss operation was obtained at pulsed powers up to 7.5 kilowatts, and at least 20 dB of isolation was maintained up to 100 kilowatts. This performance, in conjunction with a switching speed of a fraction of a microsecond, permits the use of these circulators for transmitting-receiving functions in high-reliability RADARs.

Adaptive signal processing for ionospheric distortion correction

Abstract: : Ionospheric distortions limit the usable signal bandwidth of HF over- the-horizon paths. By measuring the transfer function of the path and correcting for it in real time, improved bandwidth capability results. To determine the feasibility of such a real-time correction technique, data has been gathered on an HF link. A non-real-time computer simulation of a correction technique has shown that for the bandwidths analyzed, the correction technique is feasible and that the corrections will not deteriorate significantly for several seconds.

Receiver for detecting signals within a predetermined bandwidth

Abstract: A receiver for detecting the presence of a signal, said receiver including a first multiplier for multiplying together the signal to be detected and a signal at substantially the same frequency as the signal to be detected, a second multiplier for multiplying together the signal to be detected and a signal at substantially the same frequency as the signal to be detected, said signals provided to the second multiplier being separated by about 90* by phase-shifting means, low-pass filters coupled to the output of each of the multipliers and a detector for combining the signals from the filters and sensing if the combined level thereof is greater or equal to a predetermined level.

Method and apparatus for transmitting time compressed audio information

Abstract: This specification discloses a method of storing, transmitting and selectively retrieving a large quantity of information such as audio signals over a wide bandwidth communication system such as television. An entire block of such information is recorded at a real-time rate, rapidly transmitted in its entirety at a greatly accelerated rate by a relatively wide bandwith signal, received and re-recorded at substantially the same accelerated rate for subsequent reproduction of the audio information at a real-time rate. Several specific methods and apparatus are disclosed for carrying out these concepts.

Compressed bandwidth transmission sysem

Abstract: A system for reducing the required bandwidth in a facsimile data transmission system or the like in which a two level digital signal, which may be derived from an analog scanning signal, is caused to be converted into and transmitted as a duo-binary signal whenever the digital signal pulse rate is greater than a predetermined minimum and transmitted as a binary signal whenever the pulse rate is lower than the predetermined rate. The system operates to produce signals which vary from an intermediate level representing black to one of two outer levels representing white as long as each black representing pulse is longer than a predetermined duration. If the black pulse is shorter than the predetermined duration the signal changes to vary between the intermediate or black level and the other lower or white level. A two level to three level converter comprising a differential amplifier and a flip-flop is shown as well as a digitally operated toggle switch for switching the level converter. In addition, a novel analog to digital converter utilizing a differential amplifier operating about an average DC slicing level is disclosed.

An Optimum Squaring Loop Prefilter

Abstract: Squaring loops are often discussed as a means of establishing a coherent carrier reference for bi-phase PSK modulation. The optimal presquaring filter is derived under the assumptions that the modulating spectrum as narrow with respect to the carrier frequency and that the phase-locked loop bandwidth is much narrower than the modulating spectrum.

Wideband CW amplification in X band with gunn diodes

Abstract: Amplification has been obtained over the whole X band with short highly-doped GaAs samples. A theoretical analysis has been used to derive the impedance from a matrix equation. This paper will cite several mechanisms, including the blocked domain model.

Signal to noise ratio studies of PIM and PIM-FM systems†

Abstract: For a PIM system, wherein the total noise power is the contribution due to d.c. and harmonic powers, an expression for signal to channel noise ratio has been established and it is shown that such a system is superior to an equivalent FM system by 1.6 dB for a bandwidth of 45 KHZ. Consequently a PIM-FM system is studied and this study reveals that it is bettor than an equivalent FM-FM system by 7 dB for a first-stage bandwidth of 45 KHZ. A generalized curve of d.c. noise power valid for the frequency range of 45 to 100 KHZ (applicable to RWM, PLM, PPM and PIM) has been drawn and the total noise power in PIM as a function of channel bandwidth is plotted alongside. The frequency spectrum of PIM-FM signals is analysed and the number of frequency components is 1134. A table has been developed (not given here), with the help of which it is possible to determine the amplitude of any desired frequency component.

Linear Microwave Solid State Transferred Electron Power Amplifiers with a Large Gain-Bandwidth Product

Abstract: In this paper we shall describe recent results with reflection type wide band solid state power amplifiers which show promise of replacing tubes in many microwave systems These amplifiers are fabricated from epitaxial GaAs transferred electron devices which are stabilized through the use of low impedance circuits to form stable wideband linear cw amplifiers Output powers in C-band of more than 250 mW over a 1 dB bandwidth of 3 GHz with a gain of 7 dB have been achieved Saturated power outputs of 1 watt with 3 dB gain have also been achieved In X-band, power outputs of over 150 mW over a 2 GHz bandwidth with 4 dB has been achieved

An Improved Read-in Technique for Optical Delay Line Correlators.

Abstract: Optical methods of information processing have become very attractive mainly due to high spatial resolution and bandwidth existing at optical wavelengths, which imply the capability of handling extremely high densities of information. Since the action of optical delay line correlators is based upon the interaction of ultrasound with light, realizable density is determined by the resolution of ultrasound, the read-in mechanism. This paper reports on a new technique capable of reading an increased amount of information (in terms of delay time) into a given aperture. The technique is to stack delay channels into the third dimension, or perpendicular to the aperture. Experimental measurements of channel cross talk parameters and the results obtained from a two-channel correlator are given.

Reuse of the frequency spectrum at the satellite

Abstract: The total bandwidth available at a geostationary satellite could be increased by reusing the same frequency band in multiple independent Earthward beams. Such beams could be utilized either for distribution services in nonoverlapping areas or for point-to-point communications services. This paper addresses the technique of frequency reuse at the satellite with the objective of obtaining an indication of the relative importance of the various parameters. The interference aggregate caused by unwanted cochannel transmissions is estimated for several satellite antenna side-lobe models. Using these results, calculations are performed of the maximum number of reuses of the frequency spectrum. The effects of both the modulation methods as well as the interference noise allocation are discussed. Finally, some geographical and traffic problem considerations are given.