Showing papers on "Keying published in 1973"

A survey of the communication theory literature: 1968-1973

Abstract: This paper surveys the literature on communication theory from 1968 to 1973. A large part of this literature, and of this paper, deals with digital communication through linear dispersive channels. Error rate bounds for pulse-amplitude modulation systems, the optimization of linear transmitters and receivers, and adaptive equalization are topics discussed initially. Important results from the literature on non-linear receivers are described next, including decision feedback, maximum-likelihood, and Viterbi algorithm approaches. New results on the conventional digital modulation formats of amplitude, phase, and frequency-shift keying are summarized. The paper concludes with sections describing the literature from this period on nonlinear and non-Gaussian problems, analog communication, and feedback communication.

Unified Analysis of a Class of Digital Systems in Additive Noise and Interference

Abstract: A unified approach is presented for evaluation of the error probabilities of a class of digital communications systems in additive noise and interference. This class of systems includes coherent systems such as M -ary amplitude-shift keying (ASK), M -ary phase-shift keying (PSK), and M -ary amplitude-and-phase keying (APK); it also includes differential coherent systems such as binary differential PSK (DPSK). The noise is not necessarily Gaussian. The interference can be intersymbol interference, co-channel interference, adjacent-channel interference, any of their linear combinations, or intermodulation prodducts at the output of some nonlinear device. This approach essentially expands the characteristic function of the interferences into a power series so that the desired error probability can be evaluated as the sum of terms representing perturbations around the error probability due to additive noise alone. Bounds on three kinds of truncation errors, which are simple and applicable to all aforementioned digital systems, are obtained. As a result, any desired accuracy in the evaluation of the error probabilities can be achieved with this approach. In the special case in which the noise is Gaussian, explicit bounds on truncation errors are also obtained. Examples are given to illustrate how the unified analysis can be applied to evaluate the error probabilities of various digital systems. More specifically, the combined effects of Gaussian noise, intersymbol interference, and co-channel interference on the error performance of M -ary coherent PSK and APK (MCPSK and MCAPK) systems are computed. The probability of error of a binary DPSK (BDPSK) system in the presence of Gaussian noise and intersymbol interference is analyzed. The intermodulation products at the output of a hardlimiter are also determined.

Printed circuit connector and keying structure

Abstract: A printed circuit connector is provided comprising a plurality of open-topped channels having an array of spring fingers therein adjacent one side of each channel. Some of the spring fingers include integral portions extending transversely across the bottom of the channel toward the other side of the channel. An elongated keying structure is removably locked within the channel, adjacent the spring fingers, to assure that only a preselected circuit board may be inserted into the channel sufficiently far to make electrical contact with the spring fingers. The lower edge of the keying structure is notched to straddle the transverse spring finger portions, and to engage the bottom of the channel between said transverse portions, thereby to transfer forces imposed upon the keying structure, open insertion of a printed circuit board, away from said transverse portions and directly to the bottom of the channel.

Receiver for dfsk signals

Abstract: Apparatus for receiving double frequency shift keying signals (DFSK) employs a phase locked loop as the frequency discriminator for tracking the four frequency states. A floating detector establishes reference voltage levels for a trio of comparators which form a binary code indicative of the number of these levels exceeded by the input signal. This code is converted by logic into mark and space signals which are held in a register until transferred to the output devices by a strobe signal.

Sine-cosine frequency tracker

Abstract: A sine-cosine frequency tracking system is provided for tracking the center of power of a Doppler type input signal. The system of the invention includes a discriminator connected in an error feedback loop, and which develops an error signal whenever the center frequency of the input signal differs from the frequency of a pair of sine-cosine keying signals. The aforesaid discriminator incorporates solid state integrated circuitry, and it is constructed to eliminate the need for difficult trim adjustments which are necessary in the prior art systems. The aforesaid discriminator also serves to improve the accuracy of the system by removing error sources present in the prior art systems.

Format control system for positioning final copy printed text

Abstract: A system for positioning final copy printed text, upon a first printing, at a specified location on a line in a format determined by input keying. The location can be a blank block on a form to be filled in. After initial setup and during any input or output operation, a final copy printed text mode can be entered by an operator and stored. This will inhibit printing upon further keying until a carrier return is keyed following the text. The printer carrier is positioned through spacing, backspacing, tabbing, etc. relative to the left side of the block, and codes representative thereof are also stored. When the carrier is at the left side of the block, the keying of a variable space or character will define a tentative format and this location, and a variable space or character code will be stored. Then the text is keyed and stored. After the text has been keyed, the keying of spaces, backspaces, tabs, and/or variable spaces will result in codes representative thereof being stored and the final copy text format being finalized. When the carrier is located at the right side of the block, a carrier return is keyed and this location is defined by the storing of a segment end code. The carrier is then automatically returned to the position occupied at the time of keying the final copy printed text mode. Thereafter, the carrier is positioned at the beginning print point for the format determined by input keying, and the final copy text is printed.

Digital frequency-shift keying receiver

Abstract: A digitally implemented frequency-shift keying receiver receives an input periodic oscillation signal of a first frequency, designated a binary "1" and of a second frequency, designated a binary "0". A unidirectional pulse is generated each time the input signal passes through a reference voltage, either positive going or negative going. The time between pairs of these pulses is measured by starting a free running counter with a first pulse and by stopping and re-starting the counter with a second pulse. If the time between two of these pulses is sufficiently long, an up-down counter counts in one direction and if the time is sufficiently short, it counts in the other direction. The up-down counter, by providing a prescribed number of counts in either direction to reach a threshold, effectively filters the input signal. An output stage, responsive to the threshold of the up-down counter, provides either a binary 1 or a binary 0.

Electronic keying circuit with selectable sustain characteristics

Abstract: Post-keyswitch-release and percussion sustain keying circuits in which a variety of player selectable sustain control signals applied to a sustain control terminal coupled to a time constant circuit through a diode gate produce differing modes of sustain and in some modes player settable sustain intervals. In addition, several octave groups of percussion sustain keying circuits having the same timing circuit component values have scaled sustain time constants by varying the sustain control signal applied to each octave group.

Anti phase-ambiguity for phase-shift keying binary transmission systems

Abstract: A circuit arrangement to eliminate the phase ambiguity at a receive terminal in phase-shift keying binary transmission systems. The received PSK binary signal is simultaneously applied to a conventional synchronous demodulator and a so-called nonambiguous demodulator which may be in analog or digital form. The outputs from both demodulators are compared to provide a signal having a first state when both demodulator outputs are in phase and having a second state when said demodulator outputs are in phase opposition. Logic means are provided to detect the state of the comparison signal in order to control inverter means adapted to reverse the demodulated original message from the synchronous demodulator when said comparison signal is in its second state.

Repetitive keyer actuating circuit for an electrical musical instrument

Abstract: In an electrical musical instrument of the keyboard type having a plurality of selectively played keys for connecting corresponding tone generator keyers to a source of keying voltage, a repetitive keyer actuating circuit operable in response to key playing to produce electrical keying pulses for alternately and repeatedly actuating two sets of keyers. The repetitive keyer actuating circuit comprises a keying pulse generator in circuit with the voltage source and the keys and operable in response to key playing to alternately and repeatedly provide at each of two outputs keying pulses at regular preselected time intervals, and keying pulse sustain circuits each in corresponding circuit arrangement with one of said outputs and a set of keyers and operable to produce multiple stage envelope decay for said keying pulses. Each set of keyers is actuated by an initially percussive and subsequently sustained keying pulse to provide musically satisfactory repeatable effects throughout the range of keying pulse frequencies.

Bass system for automatic root fifth and pedal sustain

Abstract: An improved system is provided for automatically playing bass notes for root and fifth parts of manually held accompaniment chords, including diminished and augmented chords, and for performing pedal sustain keying functions. Latching circuits are provided which respond to actuation of playing keys or pedals and which store the response to the last pedal actuated. The system also includes circuitry for keying bass tones for actuated pedals and for the root and fifth parts of manually played chords. This circuitry includes a set of gates which are each enabled by an associated latching circuit, inhibited by other latching circuits, and inhibited by outputs from other operated gates. The system further includes keying bus sensing and controllable ratio frequency dividers to cover a multiple octave range and to reduce the number of pins required for an integrated circuit pack to implement the system.

Spread Spectrum System Using Noise Band Shift Keying

Abstract: A new spread spectrum technique using band-limited Gaussian noise for transmission and incoherent detection at the receiver has been discussed. The proposed system called noise band shift keying (NBSK) may be considered as a modified form of the frequency-shift keying (FSK) system. In the NBSK system nonoverlapping bandlimited noise is transmitted instead of pure tones as in the FSK system and the center frequency of the noise is chosen on the basis of the binary data signal. For this system, an expression for the probability of error has been derived and it has been shown that its performance under nonfading channel conditions is identical to that of the FSK system with frequency diversity under Rayleigh fading conditions. Compared to the conventional spread spectrum systems, the proposed method is considerably more simple to implement and is attractive where adequate bandwidth is available.

Automatic performance system for electronic instruments

Abstract: The keying patterns for a performance on an electronic instrument are recorded on a magnetic tape from which they can be reproduced to automatically control the instrument and reproduce the performance. The recording density is greatly increased by intermittently driving the recording medium past a recording head through a predetermined distance only when the keying pattern varies.

Optimum Deviation Ratio and Observation Interval for Continuous-Phase Binary Frequency-Shift Keying

Abstract: The optimum deviation ratio ( h =1/2 ) and observation interval (2-b periods) for a continuous-phase binary frequency-shift keying (CPBFSK) signal have been determined analytically for particular length sequences based on a squared-distance criterion.

Discovery in keying circuit for a musical instrument

Abstract: An electrical musical instrument includes a series of tone signal sources under the control of upper manual, lower manual and bass pedal key switches operatively connected to an output system. A further keying circuit includes further keyswitch means under the control of the lower manual which selectively operate a current-mode logic network which in turn drives an audio gating means connected through a single bus to the output system. A rhythm pattern generator has one output that keys said bus and a further output that controls enabling circuit means, namely a two-phase driver portion thereof that alternately energizes two current source portions which are respectively connected to the current-mode logic network whereby bass notes corresponding to the lowest and the highest keys depressed on the lower manual are reproduced by the output system in accordance with the rhythm pattern.

Percussion to direct keying switching circuit for an electrical musical instrument

Abstract: In an electrical musical instrument having a plurality of selectively played keys each for connecting a tone generator keyer to a source of keying voltage through a related percussion keyer circuit, a percussion to direct keying switching circuit for selectively providing percussion and direct keying operation of all of the tone generator keyers by operation of a single control switch.

Circuit connecting device

Abstract: The SPST transmitter keying switch is used both to operate a transmitter keying relay and switch the audio amplifier power on and off. A diode is used to isolate the relay and amplifier power supplies.

An Evaluation of Modulation Systems

Abstract: : The report summarizes the results of a theoretical and experimental study of the relative strengths and weaknesses of amplitude shift keying, phase shift keying and quadriphase shift keying systems. The report is a combination review report and research monograph. Ideal theoretical results are discussed, and methods of practical realization are described. New research results include the determination of the standard deviation of the arrival time as a function of modulation, simple formulas for the degradation in both digital and analog systems due to adjacent-channel interference, and simple upper bounds for intersymbol interferences. The use of the formulas are all examined experimentally.

Apparatus for accelerating D.C. transient decay by independent keying of a balanced demodulator

Abstract: For use with analog a.c.-to-analog d.c. conversion systems or the like employing balanced demodulators for reducing settling time i.e., the interval between application of a.c. superimposed on d.c. and the provision of a d.c. analog of the superimposed a.c., means for introducing an independent keying signal to force demodulation during part of the settling time.

High voltage protection circuit

Abstract: A voltage dependent resistor is cooperatively coupled with a keyed automatic gain control device to provide control signals sufficient to bias off the radio and intermediate frequency amplifier stages of a television receiver when the amplitude of the keying pulse reflects an open-circuiting of a horizontal retrace capacitor which raises the developed high voltage to an excessive level.