Showing papers on "Bandwidth (signal processing) published in 1975"

GaAs electro‐optic directional‐coupler switch

Abstract: We report the fabrication and testing of a GaAs electro‐optic directional‐coupler (EDC) switch in which the fraction of light coupled from one waveguide channel to the other can be controlled by an applied electric field Ninety‐five percent amplitude switching and a maximum extinction ratio of 13 dB have been observed in an EDC switch, having a minimum 3‐dB bandwidth of ≳100 MHz and a drive power per unit bandwidth of <180 μW/MHz

RF Spectrum of a Signal after Frequency Multiplication; Measurement and Comparison with a Simple Calculation

Abstract: A novel experimental technique is introduced and used to measure the effect of frequency multiplication on the RF spectrum of an oscillator. This technique makes it possible to produce the RF spectrum at X band?where measurements are relatively straightforward?that would have been produced by frequency multiplication of the 5-MHz source to any frequency from 9.2 GHz to 100 THz (1014 Hz). A simplified theory is developed and shown to reproduce the experimental results for the relative power in the carrier and noise pedestal, and the shape and the width of the carrier and noise pedestal, to within the measurement uncertainty of 2 or 3 dB, from 5 MHz to 10 THz. The calculations are easily made using analytical techniques from the measurement of the spectral density of phase fluctuations of the source, the effective input spectrum density and the bandwidth of the multiplier chain, and the frequency multiplication factor. It is shown that present 5-MHz-crystal-controlled oscillators are useful as a precision source to ~500 GHz. Suggestions for extending their range to ~100 THz are made.

Component Signal Separation and Recombination for Linear Amplification with Nonlinear Components

Abstract: LINC is a technique that uses signal processing to produce linear amplification of bandpass signals with grossly nonlinear circuit components. Two important signal-processing functions of LINC are 1) forming two constant envelope phase-modulated signal components from the bandpass input signal and 2) recombining the amplified components to produce an amplified replica of the input signal. Two-tone laboratory tests of a LINC component separator and combiner, not including a limiter and envelope detector, show that, at full output, spurious levels 40 dB below tone level are achievable over a 1-MHz band. Because the laboratory model operated at relatively low frequencies (hundreds of megahertz), scaling up in frequency should result in a LINC with <40-dB spurious over a 10-MHz band. Spurious 30 dB below tone level should be achievable over a bandwidth of 50 to 100 MHz using the same technique of component signal separation. Lower spurious levels or greater bandwidths will require a sin-1phase modulator that is less sensitive to delay in a feedback loop.

Method for optimizing the bandwidth of a radio receiver

Abstract: A method is disclosed for optimizing the bandwidth of a radio receiver cale of receiving widely varying input data rates. The method may be utilized with known superheterodyne receivers having certain modifications to allow for the ability to vary the intermediate frequency and the center frequency of the associated bandpass filters over a continuous range of values. The method includes the steps of determining the optimum intermediate frequency bandwidth for a given input data rate, adjusting a tunable bandwidth filter to a center frequency which is a predetermined multiple of the desired intermediate frequency bandwidth, and producing an intermediate frequency equal to the tuned frequency of the filter.

Compatible stereophonic receiver

Abstract: A compatible stereophonic receiver capable of receiving a monaural signal, 2-channel stereophonic composite signal and multi-channel composite signal transmitted in the frequency modulated form, which comprises a plurality of band amplifiers each having a bandwidth different from each other so as to amplify an intermediate frequency signal including any of the above-mentioned signals; a discriminator for determining whether the signal received is a monaural signal, 2-channel composite signal, or multi-channel composite signal; and means for selectively connecting a band amplifier which has a bandwidth corresponding to an output signal from the discriminator to a multiplex demodulator through a frequency modulated wave detector and controlling the multiplex demodulator to demodulate an audio signal from the output of the frequency modulated wave detector.

Communication systems using bundle conductor overhead power lines

Abstract: The main properties of power line carrier (p.l.c.) systems, used conventionally for internal communication purposes in electricity supply undertakings, are examined, and an alternative method for use on bundle-conductor lines is proposed. Earlier work, departing from the use of conventional phase-ground or interphase carrier, proposed the electrical separation of the subconductors of a bundle for signal frequencies, but retained the remaining aspects of conventional p.l.c. These include particularly the expensive filter components required to limit the signal, as far as possible, to the desired parts of the power network, together with the frequency and bandwidth limitation imposed on the signal by these filters. The intrabundle communication system proposed uses a simple, inexpensive but highly efficient broadband coupling method which permits signal-isolation between subconductors without inserting additional impedance at power frequency or reducing the power transmission capability of the line. The signal characteristics of the new system are such that interference is reduced by orders of magnitude in comparison to p.l.c., avoiding need for frequency assignment even between adjacent phases. A bandwidth of 1.6 MHz is available. This may be exploited in a variety of ways, including the transmission of data at faster rates, to enhance the reliability and speed of protection signalling, or to provide up to 180 duplex voice channels. Even where one voice channel only is required, the cost of an intrabundle communication system is estimated to be less than that of a p.l.c, system for route lengths of at least 29 km, and allows subsequent increase in the voice channel numbers at low extra cost.

Voice-excited predictive coding system for low-bit-rate transmission of speech

Abstract: Voice‐excited speech analysis synthesis systems eliminate two of the most difficult tasks in speech analysis, namely, voiced‐unvoiced decision and pitch analysis They can therefore perform better than pitch‐excited systems under practical speaking conditions However, the transmission rates for voice‐excited systems are usually much higher than for pitch‐excited systems, owing to the additional bits needed for encoding the baseband This disadvantage can be overcome by efficient encoding of the baseband This paper presents a voice‐excited predictive coding method for speech transmission at 2400 to 3600 bps The analytic signal corresponding to a baseband of 300 to 900 Hz is square‐rooted to reduce its bandwidth to 300 Hz and is encoded at 1200 bps by predictive coding At the receiver, the wide‐band excitation is derived by nonlinear distortion and inverse‐filtering of the baseband The speech signal is sampled at 667 kHz, and its spectral‐envelope information is transmitted every 20 msec by 10 area parameters obtained by the linear prediction method These parameters and the rms value of the speech signal are encoded at 1800 bps, yielding a transmission rate of 3000 bps for the speech signal

Common medium optical multichannel exchange and switching system

Abstract: In the disclosed common medium multichannel exchange and switching system, optical carrier frequencies and bandwidths are employed and provide switched channels of unprecedentedly large bandwidth. At the same time, the switching network at optical frequencies is of such unprecedentedly small size that it promises to be implementable via integrated optics on only one integrated circuit chip, or, at most, a few chips of suitable material. The system is adapted to optical frequencies in that the common medium is an optical strip guide and optical directional channel-separation filters are employed to couple a plurality of switched customers or switched facilities on to or off of the common medium. At the same time, the system is compatible with the central processing control of the general type employed in current electronic switching systems. In one embodiment, some of the directional channel-separation filters are tunable over the entire bandwidth of the system without compromising the small size of the integrated optics network by employing a variable diffraction-grating effect induced by an acoustic wave. A second embodiment provides distributed switching employing a looped common medium.

Color encoding filter and method for making the same

Abstract: A color encoding or dichroic filter for video transmission and method of making the same is provided The color encoding filter can be used with a vidicon tube to provide color signals for video transmission The filter comprises a substantially transparent substrate, such as glass, having a plurality of grid patterns superimposed thereon with each pattern individually or in conjunction with an overlapping grid pattern capable of transmitting a predetermined bandwidth of energy A substantially transparent filler material is utilized to complete the filter structure The filler material is substantially transparent to the desired transmitted bandwidth of energy and is further optically complementary to the filter material of each individual grid pattern to minimize any refractive scattering of transmitted energy The filler material also provides both a planar exterior surface to the filter and further permits the filter material of the overlapping grid patterns to be maintained with a constant thickness

Mobile diversity radio communication system

Abstract: A diversity system in a mobile radio communication system provided with a plurality of antenna systems operating over a multipath medium in at least one of the sending path and the receiving path. At the sending path, a carrier wave frequency- or phase-modulated by a digital baseband signal is transmitted from a transmitting antenna. A plurality of receiving antenna systems are switched at a constant frequency higher than the signaling rate of the digital baseband signal but less than the frequency shift width of the frequency modulated wave or less than a product of the maximum phase shift of the phase modulated wave and the signaling rate, so that average-power dispersion in a signal element of the digital baseband signal received at the receiving antenna systems is effectively compressed. Alternatively, the plurality of antennas may be transmitting antennas, and switched at the same rate to achieve compression of average power dispersion in the baseband signal elements.

Methods and apparatus for reducing the bandwidth of a video signal

Abstract: Alternate lines of a 526 line video signal are time-stretched and transmitted over a transmission channel of limited bandwidth. At the receiver, the lines are compressed back to their original duration and displayed in an interlaced manner on a conventional receiver by blanking alternate lines in each field. In another embodiment of the invention, adjacent transmitted lines of the video signal are averaged at the receiver and the resultant signals are substituted for the non-transmitted lines of the video signal.

A recursive time‐varying band‐pass filter

Abstract: Time‐varying, digital band‐pass filters are extensively used in seismic data processing, since the dominant frequency of reflected signals usually becomes lower and their bandwidth narrower with the passage of time. In routine seismic data processing, time‐varying, digital band‐pass filtering is stepwise.

Digital pulse compression via fast convolution

Abstract: The mathematical structure of the digital ambiguity function for a matched filtered linear FM (LFM) waveform is derived as a function of time-bandwidth product, sampling rate, and arbitrary delay and frequency shifts. It is found to be well behaved for sampling rates equal to or greater than the swept signal bandwidth, provided that time sidelobes are controlled using standard frequency domain weighting techniques. A digital convolution processor comprised of cascaded pipeline fast Fourier transforms (FFT's) is presented as a viable architecture for real-time filtering of moderately high bandwidth LFM signals, and tradeoffs among radix, pipeline clock rate, and convolutional efficiency are discussed. It is found that a modified floating-point computational scheme performs well in such a context and is especially useful if a large signal dynamic range must be accommodated. A radix-4 4096-point design example is considered and the effects of quantization and finite register length arithmetic upon the digital ambiguity function are demonstrated via simulation. It is found that input data, FFT coefficients, reference filter coefficients, and intermediate results can be represented with mantissas of modest bit length.

Frequency discriminator apparatus

Abstract: A frequency discriminator having at least one ferrimagnetic resonator in a band pass or band reject configuration, the frequency of which is swept over a frequency band of interest, a detector receives the filter output, and the timing relationship between the detector output and the swept frequency is compared to generate the discriminator output. The discriminator has a bandwidth variable from a relatively narrow range to a very wide range in which the center frequency is simultaneously tunable over an extremely wide frequency range. The discriminator is insensitive to amplitude variations of the input signal and is capable of demodulating low level signals. The frequency discriminator is particularly useful for microwave frequency applications, for example, as a discriminator in a simple microwave FM receiver.

Minimax spectrum shaping with a bandwidth constraint.

Abstract: A new approach to spectrum shaping, in which the maximum of the spectrum is minimized subject to a constraint on the bandwidth, is considered. The results can be applied to a variety of methods of digital holography. A lower bound for the maximum and a figure of merit are obtained. Practical methods for minimax shaping of the spectrum are described and compared via computer simulations. The results of these simulations indicate that the lower bound is relatively tight, and the figure of merit is a good one.

Measures of spectral efficiency in land mobile radio

Abstract: Measures of spectral efficiency are very important to the resolution of contemporary issues in Land Mobile Radio (LMR), because they (a) allow the comparison of existing and proposed systems in terms of their spectral efficiency; (b) permit estimates to be made of the ultimate capacity of various system types at different levels of development; and (c) are useful in setting minimum standards for spectral efficiency. The purpose of this paper is to review the advantages, disadvantages, and limitations of various measures of spectral efficiency that have been proposed.

Television signal processing apparatus including a transversal equalizer

Abstract: Signal delaying means, included in the luminance channel of a color television receiver, are responsive to the television video signal processed in the receiver. A portion of the signal delaying means serves to equalize the time delays of signals processed in the chrominance and the luminance channels of the receiver. A plurality of differently delayed video signals are developed at signal coupling means associated with the signal delaying means. At least two of the delayed video signals, spaced apart in time by a predetermined interval inversely related to a frequency at which it is desired to relatively attenuate the video signals, are combined to determine the peaking characteristics of the luminance channel. At least one other of the delayed video signals is used to produce a signal to control the bandwidth characteristics of the luminance channel. Additional means may be provided to allow the amplitude of the output signal derived by combining the peaking and bandwidth controlling signals to be controlled so that signals processed in the luminance channel may be either peaked or depeaked, depending on the quality of the incoming video signals.

Matrix Bandwidth and Profile Reduction.

Abstract: This program, REDUCE, reduces the bandwidth and profile of sparse symmetric matrices, using row and corresponding column permutations It is a realization of the algorithm described by the authors elsewhere It was extensively tested and compared with several other programs and was found to be considerably faster than the others, superior for bandwidth reduction and as satisfactory as any other for profile reduction

Programmable Matched Filtering with Acoustoelectric Convolvers in Spread-Spectrum Systems

Abstract: : Acoustoelectric convolvers for a spread-spectrum communication application are described with a 100-MHz-bandwidth capability. The use of convolvers as programmable matched filters provides the ability to change the coding waveform from bit-to-bit, thus offering improved multipath performance, security against decoding, and protection against repeat jamming. In this paper we describe design and performance details of a prototype convolver which processes signals of 10 microseconds duration with a 100-MHz bandwidth. A dynamic range of 50 dB is obtained and error signals are 30 dB below the output signal with input signal levels of +14 dBm. A test circuit is described which creates typical spread-spectrum signals in which each bit is encoded into 512 chips and data is encoded by inverting the phase of an entire bit at a data rate of 100 kbits/s. Examples of typical convolver outputs will be described, including spurious artifacts due to a pseudorandom-shift-register code, with a code-cycle time of 36 minutes. (Author)

Smoothing of irradiance spectra with finite-bandwidth windows, with application to particle-size analysis

Abstract: We investigate the problem of obtaining minimum-bias spectral estimates under the constraint of finite spectral-window bandwidth. The problem is meaningful for spectral estimation with a coherent optical system in which the power-spectrum estimate, i.e., the Fourier irradiance, is physically available for smoothing. An example that deals with the smoothing of statistically unstable optical data is furnished in connection with the problem of particle-size estimation with an optical-digital computer. We show that the smoothing of the irradiance spectrum prior to particle-size estimation furnishes more satisfactory results than operating with unsmoothed data.

A compensation technique for a gyrator and its use in the design of a channel-bank filter

Abstract: A model proposed recently for an operational amplifier gyrator circuit is used to develop a compensation technique whereby the useful bandwidth of the gyrator circuit can be increased. The compensation technique is verified first by computer-aided analysis and then by experiment. It is shown that a significant increase in the useful gyrator bandwidth can be achieved by using an inexpensive capacitor. The compensation technique is then applied in the design of a gyrator-C channel-bank filter. The influence of dc-supply voltage and ambienttemperature variations on the performance of the filter is examined.

Combination waveguide and stripline downconverter

Abstract: A frequency mixer-downconverter which can be tuned as either a single sideband mixer or a double sideband mixer and which has a wide tunable RF bandwidth and low conversion loss is disclosed. A high-frequency input signal is coupled from an input waveguide to a shielded suspended stripline. Two Schottky barrier diodes are connected proximate to the waveguide-to-stripline transition, between the inner conductor and the outer conducting channel of the stripline. The two diodes intermodulate the input signal with a subharmonic pumping signal which is also coupled to the suspended stripline from a waveguide input. An intermediate frequency signal, at a frequency equal to the difference between the input signal and twice the frequency of the pumping signal, is generated as an intermodulation product and transmitted on the suspended stripline to an output. The downconverter can be tuned as either a single sideband mixer or a double sideband mixer by positioning an E-plane waveguide tuning short and an H-plane waveguide tuning short at the transition between the input waveguide and the suspended stripline. For a single sideband mixer the tuning shorts are adjusted to provide at the input waveguide-to-stripline transition a reactive termination at the image frequency and an impedance match at the input signal frequency. The tuning shorts are positioned to provide the same impedance match at both the image frequency and input signal frequency for double sideband tuning.

Electronic music synthesizer

Abstract: An electronic music synthesizer is disclosed in which the sound producing chain includes a voltage-controlled oscillator, band-pass filter, low-pass filter, and amplifier in which selected control currents are supplied to low impedance points within the synthesizer circuit from a resistor matrix. The synthesizer produces sounds approximating different acoustic musical instruments or having different tonal qualities by the application of a predetermined voltage to one of fifteen input columns of the resistor matrix with selected other columns being grounded. The currents provided by the resistor matrix in combination with other externally generated currents control the center frequency and bandwidth of the band-pass filter, the cutoff frequency of the low-pass filter, the gain of the voltage-controlled amplifier, the time constants of transient contour currents used to control the filters and amplifier, and the waveform produced by the voltage-controlled oscillator. Specialized keyboard, waveshaping, contour generating and modulating circuits are also provided.

Compatible picturephone system

Abstract: A system for permitting compatible communications among broadband and narrowband picture telephone installations, the bandwidth of a narrowband installation corresponding to the lower portion of the bandwidth of a broadband installation, in which the pictures associated with both types of installations have the same number of lines, the same line scanning frequency and the same frame rate, both the scanning of the subject image and playback are effected with a wave-shaped line scan for playback in a broadband installation, the signals in the transmitting portion of a broadband installation are split into a low frequency component, covering a bandwidth corresponding to that of a narrowband installation, and a high frequency component, and both components transmitted from a broadband installation are recombined in the receiving portion of a further broadband installation receiving the transmitted signals.

Optimum Pulse Shapes for Pulse-Amplitude Modulation Data Transmission Using Vestigial Sideband Modulation

Abstract: When designing pulse-amplitude modulation (PAM) systems for use over bandpass channels having restricted bandwidth, one may be led to use single-sideband (SSB) or vestigial sideband (VSB) transmission in order to maximize transmission rate. Carefully shaped pulses must be used to minimize degradation due to intersymbol interference (isi). In this paper VSB pulses are derived that have no inherent isi, and in addition have maximum immunity in a mean-squared-error (MSE) sense to timing and carrier phase errors. The results here generalize on those of Franks who treated the SSB case. The optimum VSB pulses are shown to be identical to those of Franks at the band edges, and to have vestigial roll-off characteristics of a similar discontinuous nature. It is also shown that one may allocate available bandwidth to the vestigial roll-off band band and Nyquist roll-off band in any way desired. The final performance for the optimum pulse depends only on the total bandwidth used. These results are shown to apply as well to a system employing a matched filter. The case of random timing and phase errors is also considered, and optimum pulses are again found. Several mathematical properties of the optimal pulses are given physical justification and geometric insight through error ellipses, and optimal signal shapes are plotted for various cases of special interest.