Showing papers on "Keying published in 1969"

The automatic classification of modulation types by pattern recognition.

Abstract: : This report presents the preliminary results of an investigation into the use of pattern-recognition techniques to rapidly and automatically identify the type of modulation on a high-frequency radio signal. Classes of modulation initially considered include double-sideband AM, upper and lower single-sideband suppressed carrier, CW, high- and low-speed teletype (single-channel FSK), multichannel FSK, and on-off keying (Morse code). The spectrum of the signal is measured by a digital analyzer whose outputs are classified by a pattern recognizer. The spectrum analyzer and classifier are realized on a PDP-8 digital computer. The new 'nearest neighbor' type of pattern recognizer has been developed that significantly increases classification accuracy. The decision surfaces of this classifier asymptotically approach the Bayes decision surfaces with simple set size. Mis-classification rates of 5 to 10 percent have been obtained with signals recorded in a typical HF environment. Important characteristics of the system are the ability to recognize the presence of a signal when the modulation format is unknown and the ability to recognize the presence of a new signal that has not been previously encountered. (Author)

The Effects of Filtering and Limiting a Double-Binary PSK Signal

Abstract: This paper describes a digital computer simulation of a double-binary phase-shift keying system. This simulation program is used to investigate the effects of limiting action and of the shape and bandwidth of the filter on the system performance, expressed in terms of error probability

Frequency shift keying laser communication system

Abstract: An optical frequency shift keying system for representing a first binary signal condition by a first optical frequency and a second binary signal condition by a second optical frequency by means including an optical modulator biased to provide optical transmission predominantly at one of said optical frequencies during one of said signal conditions and to provide transmission at the other of said optical frequencies during the second condition.

Digital data transmission system utilizing phase shift keying

Abstract: A digital data transmission system utilizing differential phase shift keying. In the transmitter serial data bits are grouped and the carrier wave is phase shifted by an angle determined from a comparison of successive data groups. In the receiver the successive phase shifts are detected by comparing the received signal in digital form with a digital reference, at a plurality of points in each cycle. When several matches are obtained for one phase, that phase is accepted as the phase of the received signal. The difference between the phases of successive portions of the received signal is utilized to reconstitute the transmitted data. Changes in polarity of the received signal are compared with the local reference signal to generate a control for the reference.

Synchronous frequency shift data transmission system in which opposite binary characterizations are transmitted as half cycles of a first carrier signal and as full cycles of a second carrier signal

Abstract: A data transmission system in which data to be transmitted is encoded using double frequency coding, the keying signal which defines the individual bit cells being in-phase with first and second carrier signals having frequencies equal to that of the keying signal frequency and twice that of the keying signal frequency. Opposite binary characterizations (''''zeros'''' and ''''ones'''') are respectively transmitted as a half-cycle of the first carrier signal or a full cycle of the second carrier signal within the appropriate bit cells, the synchronous relationship between the keying and carrier signals providing for bit cells of equal size and self-clocking. Encoded data is processed at the transmitting and receiving ends of a transmission line by circuitry which is transformer coupled to the line at both ends to provide isolation and minimize common mode noise and ground shift problems, and which is impedance matched to the line to provide high noise immunity.

Television receiver agc system keyed in response to time coincidence of sync and flyback pulses

Abstract: Under normal operating conditions a coincidence circuit produces keying pulses, for an AGC system of a television receiver, only when the flyback pulses from the receiver''s horizontal sweep system occur concurrently with the horizontal sync components from the sync separator. The magnitude of the developed AGC voltage is held constant between keying pulses. This arrangement precludes sampling of video information, with a resulting false measure of received signal strength and an erroneous magnitude for the AGC voltage, which takes place in a conventional flyback pulse-keyed AGC system when the horizontal oscillator is out of synchronism with the sync pulses. During transient conditions, when there is a very fast and substantial increase or decrease in received signal strength causing a loss of sync pulses at the separator output, keying is achieved in the disclosed AGC system in response to the flyback pulses alone.

Time-frequency-phase in-band coded communications system

Abstract: A communication system which uses a diversity technique to overcome problems of signal fading and multipath distortion. Frequency shift keying (FSK) and differential phase shift keying (DPSK) are employed in combination to code a sequence of signals responsive to a word represented by a stream of input binary digits. The sequences of signals to be transmitted are arranged such that identification of the frequency, phase shift and location of one signal in the sequence uniquely defines the input word.

Television picture montage circuit

Abstract: A method and apparatus are described for the preparation of a common television program signal from different line scan signals. Line scan signals are generated such as of the conventional video type employed in the transmission of television programs. Each line scan signal has a like period and is applied along different channels for combination after passing through variable gain channel amplifiers. Control voltages are generated for the gain control of the channel amplifiers. The control voltages are produced from a keying signal and a composite keying signal which pass through variable gain circuits to produce directly related and complementary related outputs. Correspondingly related outputs are added with the added signals applied through a switching network for varying the gain of the channel amplifiers. By selectively controlling the keying signal particular time portions of each line scan may be controlled in the common television program signal for the superimposing of several programs. Gradual control may be obtained by varying the gain of the variable gain circuits with faders.

Rate optimization for digital frequency modulation

Abstract: The data rate of a multilevel digital FM system is optimized subject to fixed RF bandwidth, signal-to-noise ratio, and output error rate. The possibility of optimizing such a system was first considered by J. R. Pierce at Bell Telephone Laboratories. He made the observation that it is possible to send many levels slowly or fewer levels rapidly for an FM wave of fixed RF bandwidth and error rate, and that there must be a choice of signaling rate and number of levels that optimize the data rate. The rigorous treatment of this problem is the subject of this paper. The mathematical model we analyze uses frequency-shift keying at the transmitter and ideal discrimination detection with an integrate-and-dump circuit as the post-detection filter. Our results are exhibited graphically showing the various dependencies among the pertinent system parameters.

Character contour edger

Abstract: As described herein, electronically generated alphanumeric character waveforms are supplied to an image enhancer circuit which reproduces the waveforms together with detail signals occurring at the leading and trailing edges of the reproduced waveforms. The reproduced waveforms and the detail signals are aligned in time and thereafter supplied to a pair of keying circuits, respectively, which in response to the reproduced waveforms and the detail signals, supply predetermined potentials to a television channel with the result that the letter waveforms will be reproduced with predetermined color contours.

Multiplexing arrangement for electronic organs

Abstract: A single diode keying arrangement is connected for use with a plurality of keyboards, pedals, stop knobs and other switch operating instrumentalities on a time sharing basis by means of a sequential pulsing arrangement.

Keying switch assembly

Abstract: A keying switch assembly operable by means of a key includes a stationary contact member, an elastically bendable contact member having a fixed end and a movable end which is selectively operable to contact the stationary contact, and a flexible shock absorber attached to the bendable contact member for reducing shock noises. An actuator strikes against the shock absorber upon operation of the key so as to cause the bendable contact member to be silently bent, so that the movable end thereof contacts the stationary contact member.

A multi-level phase continuous fsk modulator

Abstract: : A phase continuous FSK modulator has been instrumented using digital techniques. The system allows for the selection of operating modes using multi- frequency level operation along with variable signaling rates. The principal feature of this modulation technique is its property of yielding a spectrum with a narrower bandwidth than conventional FSK at a given keying rate.

Electronic musical tone generator employing pitch compensation

Abstract: A continually operative tone oscillator has a keying network coupled to the output thereof. When the keying network is turned on, a capacitor gradually charges to a reference level. As the capacitor charges, the loading on the oscillator increases to simultaneously increase the frequency and the amplitude of the output tone. When the keying network is turned off, the capacitor discharges producing a gradual decay of the output tone. Simultaneously, the loading on the tone oscillator is decreased, thereby shifting the frequency thereof back to the original unkeyed value.

A unified performance analysis of adaptive and self-synchronizing receiving systems.

Abstract: : Various results have been achieved in unifying the analysis and interpretation of coherent and noncoherent digital data communication systems, by both theoreticians and systems engineers. This research has been concerned with an analysis, unification, and interpretation of the more significant aspects of partially coherent, adaptive, and self-synchronizing digital data receiving system concepts, under a common physical parameter framework. The partially coherent system concepts considered, consist of: (1) The Squaring-Tracking concept, (2) The Pilot-Tone or Residual Carrier concept (employing a first order loop), (3) The Differential Phase Shift Keying (DPSK) concept. Performance characteristics (error probability) for the partially coherent receiver concepts are obtained under a common and unified receiving systems framework. It is assumed that the channel phase modulation effects are tracked in a quasi-steady state mode by the reference acquisition loops, that is with a small value of dynamic phase lag. The partially coherent receivers are assumed to employ realizable filter forms. System performance is illustrated graphically along with interpretive comments and compared with ideal reception (coherent PSK). (Author)