Showing papers on "Bandwidth (signal processing) published in 1968"

A new wide-band amplifier technique

Abstract: Precision dc-coupled amplifiers having risetimes of less than a nanosecond have recently been fabricated using the monolithic planar process The design is based on a simple technique that has a broad range of applications and is characterized by a stage-gain- bandwidth product essentially equal to that of the transistors, and a very linear transfer characteristic, free from temperature dependence

Universal demodulation system

Abstract: An FM demodulation system useful to demodulate any carrier signal of any deviation within prescribed ranges with unitary apparatus. A plurality of band pass filters is employed, each filter having a predetermined bandwidth, and selected filters are operatively arranged with a plurality of frequency translators such that an input signal can be heterodyned to the center frequency of the filter having the requisite bandwidth for the deviation of the particular input signal.

PHOTOMULTIPLIER DETECTION OF 10.6 μm RADIATION USING OPTICAL UP‐CONVERSION IN PROUSTITE

Abstract: Synthetic single‐crystal proustite pumped with collimated pulsed ruby laser radiation has been used to convert 10.6 μm radiation to the visible. Measured values of photon conversion efficiency (Ns/Nir = 1.4 × 10−6) and phase‐matched bandwidth (540 A at 10.6 μm) are in good agreement with theory.

Enhancement of optical receiver sensitivities by amplification of the carrier

Abstract: The amplification before detection of the carrier of a modulated optical signal by a narrow-band quantum amplifier enhances the signal-to-noise ratio, particularly when the signal wave-front is distorted. A further improvement is obtained by using a combination of wide-band and narrow-band quantum amplifiers. The practical application of these schemes requires a degenerate regenerative ring-type amplifier capable of amplifying arbitrary transverse field configurations. Experiments show that such an amplifier with a gain of 24 dB and a bandwidth of 1 MHz is feasible. The incident beam axis can be displaced by as much as ten times the beam-waist radius without losing more than 4 dB in gain. Frequency modulation may be converted into amplitude modulation by the phase shift introduced in the carrier.

Printed-Circuit Complementary Filters for Narrow Bandwidth Multiplexers

Abstract: Design techniques and interconnection equivalent circuits are presented for constricting low-cost printed-circuit narrowband complementary filters. The techniques and circuits described allow the achievement of contiguous band multiplexers using a single printed circuit board with no series or shorted stubs. Equivalent circuit transformations useful in obtaining practical designs and experimental results for a two-section stripline complementary filter pair are also given. While emphasis is placed on printed-circuit filters, the interconnection circuits and design techniques presented can be applied in the design of narrowband multiplexers using many other filter types.

Generation of Digital Signaling Waveforms

Abstract: Data transmission (digital signaling) systems generally transmit continuous, essentially bandlimited signals that represent alphanumeric sequences. The transmitting apparatus in such systems must therefore convert discrete symbols-often binary pulses-into prescribed analog waveforms. Current commercial systems do this via simple filtering, gating, and conventional modulation. These practices limit the types of waveforms that can be used and they are not always amenable to variable rate signaling. This paper describes a hybrid digital-analog method for approximating closely almost any reasonable digital signaling waveform. The basic idea is very simple: a "staircase" approximation of the desired signal can be generated via a shift-register version of a transversal filter. Variations on this idea, such as derivative approximation and multirate shifting, enhance its accuracy without destroying its simplicity and time-frequency scalability.

Multifrequency tone detector

Abstract: 1,221,890. Telephone exchange receivers. WESTERN ELECTRIC CO. Inc. 2 Dec., 1969 [5 Dec., 1968], No. 58680/69. Heading H4K. [Also in Divisions G4-G6] A tone detector determines which one of a number of signal frequencies is present by counting the number of clock pulses between zero crossings of the received waveform, decoding AND-gates connected to the counter indicating acceptable upper and lower counts for each signal frequency and thereby providing for each frequency a recognition bandwidth to allow for the fact that the signals may originate from different sources at different times and be subject to slight variation. In the 1-out-of-4 multifrequency detector illustrated the received sinusoidal signal is squared and positive or negative going zero-crossings are signalled as spikes to drive a synch. circuit 13 which replaces an input spike with the next occurring clock pulse. The first received zero-crossing spike resets output bi-stables 24 to 27 and, after a one-clock pulse delay introduced by circuit 21, it resets the counter 22 and the recognition bandwidth bi-stables 14 to 17. If the count from this reset point reaches the lower limit 179 of the recognition band of the highest expected frequency an AND gate decoder sets bi-stable 14. If the count proceeds beyond the upper limit 189 of the recognition band an AND gate decoder resets the bi-stable 14. Bi-stables 15, 16 and 17 are similarly set and reset as the count passes through the recognition bands of the lower frequencies. If, as will occur with the reception of one of the four frequencies, the next zero crossing spike occurs when the count lies within a recognition band the operation of gates such as 18, 19 transfers the set state of one of the bi-stables 14 to 17 to the corresponding output bi-stable 24 to 27. Should the count procee. beyond the last range a gate 29 stops the count to prevent recycling and false operation in response to harmonics. Two such receivers may be used in parallel, one for 1-out-of-4 high frequencies, the other for 1-out-of-4 low frequencies, the two sets of frequencies being separated by a filter and the two receivers differing only to the extent of working with different clock frequencies.

Minimum rms bandwidth of M time-limited signals with specified code or correlation matrix

Abstract: The minimum rms (root-mean-square) bandwidth of M real equi-energy time-limited signals is derived for the case of either a specified code or a specified correlation matrix. The minimum bandwidth depends only on the nonzero characteristic roots of the correlation matrix, or equivalently, of a matrix derived from column properties of the code. The optimum waveforms depend additionally on the characteristic vectors of the respective matrix and are given by linear combinations of a time-limited fundamental sine wave and its harmonics. An upper bound on the minimum rms bandwidth is approximately proportional to the rank of either matrix. Applications to several codes and correlation matrices are given, including some best binary group codes, which indicate a worthwhile saving of bandwidth for the optimum waveforms as compared with conventional waveforms. The energy concentration of these optimum rms waveforms compares very favorably with that of the time-truncated prolate spheroidal wave functions, which concentrate most energy in an assigned frequency band. Furthermore, the optimum rms waveforms are easier to generate and process.

Distortion Compensating, Condenser‐Earphone Driver for Physiological Studies

Abstract: A design for a condenser earphone driver is given. The driver predistorts electrical input signals to counteract the inherent square‐law operation of the condenser earphone. Thus, smaller‐diameter earphones, with their wider bandwidth characteristics, can be used at stimulus levels of interest without appreciable harmonic distortion.

Optical communications system with improved bias control for photosensitive input device

Abstract: An optical communications system in which a subcarrier is impressed on an optical beam with a modulation representative of a signal to be communicated. This beam is intercepted by a semiconductor device having a photo-sensitive junction which generates an electrical signal representative of the modulated subcarrier and applies this signal to a demodulator for detecting the transmitted signal. A tuned circuit resonant at the subcarrier frequency is interposed between the semiconductor device and the detector and serves as a rejection filter for frequencies which deviate from the subcarrier frequency by more than the bandwidth of the transmitted signal. A back bias is applied to the photo-sensitive junction of the semiconductor device through a low resistance path of the tuned circuit so that the back bias does not vary substantially with variations in the intensity of optical radiation intercepted by the semiconductor device.

Television bandwidth reduction by encoding spatial frequencies.

Abstract: Fourier coding method for coding images for digital transmission, achieving bandwidth reduction for televised images

High Speed Correlator

Abstract: The real time computation of the correlation function of two signals of up to 2.5 MHz bandwidth at 30 points simultaneously has been achieved to an accuracy of better than 3% of reading ±2% of full scale by a probabilistic computational procedure. An oscilloscope display permits ``live'' observations. The maximum delay between the input signals can take values between 3 μsec and 48 msec, corresponding to delay increments of 0.1 μsec to 1.6 msec, derived from a crystal oscillator. The instrument offers an order of magnitude improvement in bandwidth and a decisive advantage in cost over commercially available units, while retaining compact size (23×48×38 cm). These features, as well as greatly simplified construction, were made possible by the extensive use of integrated circuits. The computational procedure and critical circuitry are described in detail, with briefer treatment given to auxiliary circuits and construction.

New Amplification Method for Depth Recording

Abstract: By placing a field-effect transistor (FET) directly on or near the test object and by supplying the source and drain from low-ohmic points, which follow the potential of the measuring signal with respect to earth, it is possible, with ordinary wires, to connect the test object with FET to the actual amplifier, which is placed at some distance from the test object. This is especially useful when it is not possible to place a complete amplifier close to the measuring point and when the size of a shielded or coaxial cable, used to connect a remote amplifier, causes difficulties.

Spectral Properties of Single-Sideband Angle Modulation

Abstract: The generation of single-sideband angle-modulated (SSB- \phiM ) waves compatible with conventional detection methods requires involved processing. The result of these operations yields a signal whose spectral properties are more complicated than simply being one-sided versions of the analogous double-sideband spectrum, and hence it is not obvious whether or not a saving in bandwidth results. Here the spectral properties of SSB- \phiM waves are investigated in detail when the modulating signal is a sample function of a stationary Gaussian process. It is shown that the power spectrum of SSB- \phiM is related to the modulating baseband spectrum through an integral equation. This equation is solved explicitly for small and large modulating indices, and it is shown how simple numerical techniques provide solutions for arbitrary index. It is concluded that SSB- \phiM exhibits properties very similar to SSB-AM with a strong carrier component When the modulation index is much less than unity. Therefore, if minimum bandwidth plus the attributes of incoherent demodulation are desired, and a Strong carrier can be tolerated, SSB- \phiM could find an application. On the other hand, for modulation indices larger than about 3, no advantage is gained since the SSB spectrum has a bandwidth equal to or larger than the bandwidth of conventional angle-modulated waves.

Project for a Digital Telephone Network

Abstract: A digital communication network is proposed that would integrate present telephone services and switched mediumspeed data or facsimile channels into a single general-purpose system. Efficient use of the cable plant is made through decentralization of switching and centralized control. Subscribers are connected to voice or data concentrators, and switching between different digital trunks is done in standardized asynchronous switching units. A novel synchronization method prevents any information losses. In view of the optimization of such a system, a reappraisal of basic system characteristics has been undertaken. For example, a ternarybased code system is used together with dc-balanced binary transmission. This facilitates the construction of simple noncritical terminals and repeaters. To allow all sorts of digital speech processing, such as conferencing or digital filtering, a companding law is chosen such that a linear addition of compressed samples is easily realizable. A higher than usual sampling rate of 12 kHz was chosen for several reasons: 1) simple low-pass filters in the PAM voice-concentrator are possible; 2) it allows a potential voice bandwidth of 6 kHz with a corresponding increase in telephone quality; and 3) data or picture transmission speed is considerably increased.

Gain and noise considerations in RF feedback amplifier

Abstract: An equivalent noise model from which open- and closed-loop feedback noise figure expressions are derived is presented. An analytical design procedure for feedback RF amplifiers yielding minimum noise figure is proposed. Experimental results are given.

Influence of Bandwidth Restriction on the Signal-to-Noise Performance of a PCM/NRZ Signal

Abstract: The influence of bandwidth restriction on the performance of a PCM transmission system is treated. In particular, the relationship is investigated between signal-to-noise, bandwidth, and bit-error probability of an NRZ (non-return-to-zero) signal. The detector used in the investigation contains a device that integrates the signal over the bit period. Theoretical results were obtained by a Fourier analysis of bandwidth-restricted signals and by an autocorrelation analysis of the bandwidth-restricted noise. Theoretical and experimental results are in good agreement.

Computer Aided Design of Wide-Band Integrated Microwave Transistor Amplifiers on High Dielectric Substrates

Abstract: The problem of wide bandwidth and flat in-band gain response for microwave transistor amplifiers has been reduced to the optimization of a number of important variables from computer prepared design charts. Through the general flexibility of the computer-generated data, a large variety of amplifier responses are possible using distributed circuit matching networks. As experimental verification of the overall design procedure, single-stage and two-stage octave wide transistor amplifiers were fabricated on 1inch by 1inch and 1inch by 1/2 inch 20 mil thick alumina, respectively. The experimental data gained from these units showed excellent correlation with the computer predicted response.

Electronic wave analyzer for determining the frequency and amplitude of components in a complex waveform

Abstract: A wave analyzer capable of determining the amplitudes and phases of frequency components in a complex waveform. he selection of a frequency component is determined by the frequency of an external ''''tuning'''' signal source. The selectivity or ability to resolve frequency components close to each other is controlled by a manual or automatic bandwidth switching circuit or a voltage controlled continuously variable bandwidth circuit.

Improvements in or relating to waveguide filters

Abstract: 1,133,801. Waveguide filters. STANDARD TELEPHONES & CABLES Ltd. 11 Nov., 1966, No. 50573/66. Heading H1W. A waveguide bandpass filter comprises main resonant cavities coupled by sections which are evanescent (i.e. are dimensioned below cut-off) at the passband frequency of the filter. In the form shown, the cavities C, E, G are tuned by coarse and fine tuning screws 3, 4 and the bandwidth is adjusted by means of screws 5 which affect the cut-off frequency of coupling sections D, F, H. As an alternative to screws 5, the blocks 9 forming the coupling sections may be provided with transversely slidable sections (7, Fig. 10, not shown). The filter is terminated by inductive irises 6. The Specification contains a theoretical discussion of the behaviour of the filter and detailed information on design procedure. It is pointed out that the filter propagates freely at frequencies above the cutoff frequency of the coupling sections and that it is necessary to provide means for absorbing or reflecting parasitic signals at these frequencies. Thus, the coupling section 11, Fig. 15(b) is associated with a narrow-band rejection filter comprising three resonant stubs 13 tuned by pistons 14. This may be converted to an absorptive constant-resistance filter (Fig. 16, not shown) which uses a resonant stub and a stub containing a matched dissipative load. Another form of narrow-band absorptive filter comprises a resonant-slot hybrid junction 19, Fig. 18, coupling the evanescent section 18 to a circular waveguide 20 containing a load 21. In a modification of this arrangement, the coupling section contains a section bounded by irises resonant at the rejection frequency, this cavity being coupled by a hole coupler to an external resonant cavity containing a dissipative load. The coupling section may, in addition, be provided with a series rejection filter comprising a central transverse post 30, Fig. 23(b). This behaves as a reflector and is situated at a point beyond the absorptive filter. In another arrangement (Fig. 25, not shown), the coupling section contains a cavity resonant at the rejection frequency provided with a tuning screw and a dissipative iron-dust slug. A series rejection filter (see Fig. 23) is situated just beyond the resonant cavity. Instead of using resonant rejection filters, the evanescent coupling sections may be constructed to have the properties of low-pass filters. Thus, the coupling sections 38(a), 38(b), Fig. 31(b), incorporate corrugated low-pass filters having a cut-off frequency below the parasitic frequencies. An intermediate coupling section is provided with a dissipative stub 40.

The effects of polarization rotation and phase delay with frequency on ionospherically propagated signals

Abstract: When a CW skywave signal is received on a linearly polarized antenna, polarization (Faraday) rotation produces a variation of received signal strength with radio frequency. The resulting dependence of received signal amplitude on radio frequency may impose a bandwidth limitation on pulsed signals where waveform preservation is important. A measure of this limitation, termed polarization bandwidth, is defined to correspond to the bandwidth in which the plane of polarization rotates 90\deg . Computer ray-tracing calculations were performed using a single Chapman-layer ionospheric model to determine the 1-hop polarization bandwidth as a function of geomagnetic azimuth and radio frequency. The polarization bandwidth was found to decrease with increasing radio frequency and with increasingly close alignment of the propagation path with the longitudinal component of the earth's magnetic field. Assuming a critical frequency of 9 MHz and a path length of 2000 km, the polarization bandwidth increased from a minimum of 140 kHz at 10.5 MHz and from a minimum of 70 kHz at 17.5 MHz, as the propagation direction varied from geomagnetic north to east. A model for the 1-hop ionospheric signal channel is proposed whose parameters are the rate of change of polarization rotation with frequency and the phase versus frequency characteristic of the path. These two parameters are shown to be readily determined from FM-CW or equivalent oblique-path sounding records. Using this model, predictions are made of the effects of polarization rotation with frequency, and also of ionospheric dispersion or phase distortion, on the envelope shape of short-pulse signals (of from 1.5 to 50 \mu s duration). A pronounced waveshape distortion due to the effects of polarization rotation on the pulse envelope was observed when the signal bandwidth appreciably exceeded the "polarization bandwidth" for the path.

Narrow band frequency modulated jammer

Abstract: A narrow band frequency modulated jamming device comprising a noise source, a low-pass filter, an amplifier and a traveling-wave tube capable of being modulated by the application of a signal to the helix thereof. Said low-pass filter is coupled to the noise source and removes or suppresses all generated frequencies above 500 Hz. The output terminal of said filter is connected to the amplifer which in turn is coupled to the helix of the traveling-wave tube. The gain control of the amplifier is adjusted so that a predetermined level of noise voltage is applied to the helix of the traveling-wave tube. This narrow bandwidth of noise serves to modulate the input signal to the traveling-wave tube. Said modulated input signal is then retransmitted as a jamming signal having a very narrow RF bandwidth and good carrier suppression.

Spectrum analysis radar system

Abstract: A radar system and method in which the returned target signal is added to a reference signal derived from the original transmitted signal. The power spectrum of the sum signal is modulated. The modulation frequency is a linear function of the range and is measured to determine the range to a target. The transmitted signal must be time stationary (i.e., a noiselike signal) and the range to the target must be equal to or greater than the ratio of the speed of light divided by the bandwidth of the signal.