Showing papers on "Keying published in 1968"

Optical ticket reader and encoding means

Abstract: An optical ticket reader and encoding means utilizing fiber optics for illuminating and reading a specially prepared ticket or other surface having optically recognizable indicia arranged on an optically recognizable background A ticket is passed over a plurality of sensors, one sensor being provided for each group of indicia to be read, which illuminate and read the ticket The information thus read is then encoded in binary form Additionally, keying indicia on the ticket are provided to indicate the general information contained on the ticket, these keying indicia being read by the reader and interpreted by the encoder to form a binary bit train correlative to the information read The keying indicia are also used by the optical ticket reader to check the accuracy of the optical reader

Chroma deying system utilizing remote controlled chroma keyer

Abstract: A chroma-keying system is disclosed which utilizes a keying signal source which is responsive to a particular color of interest from a video source. The keying signal source is continuously adjustable so that any color may be selected from the video source. Whenever the selected color exceeds in amplitude a threshold level established at a keying amplifier, the amplifier causes an appropriate output device to be switched from one television camera to another to thereby create a special effects signal at the device. When the keying signal decreases in amplitude below the threshold level of the keying amplifier, the output device is switched back to the original camera. With a single control remotely located from the chroma-keying system (at the operator console, for example), the operator can continually adjust the color of interest from the video source and thus, the special effects signal at the output device can be continuously adjusted, if so desired.

FM "Chirp" Communications: Multiple Access to Dispersive Channels

Abstract: The white Gaussian noise-limited channel so often assumed by system designers is encountered less and less in practice as the density and sophistication of modem communications increase. Long-range radio communications in particular tend to be limited by interference rather than by receiver noise; for that reason, the design of the signal waveform has great impact on system performance. A waveform that shows particular promise for channels such as satellite relay and HF radio is swept FM or "chirp" modulation. The chirp waveform is characterized in Fig. 1. A carrier is swept in frequency over a band W during a sweep interval T. The sweeps shown are linear and assume a square amplitude envelope of unity value, although nonlinear sweeps and shaped envelopes may be used. The sweep slope W/T may be used to convey information in a variety of ways, the simplest being +W/T for binary 1 and -W/T for binary 0 (slope-shift keying SSK). Higher order alphabets can be represented by different slopes, and amplitude can be added if desired. SSK will usually be most efficient, reserving the distinguishability of different slopes for the purpose of defining channels or addresses in multiple-access applications. The value of chirp modulation derives from its efficient use of available bandwidth and transmitter power in combating multipath and other forms of interference, including the "clutter" of other transmissions in multiple-access systems.

Binary to ternary protected code converter

Abstract: A first code converter comprising two shift registers, one with a counter, and a logic circuit for converting binary code signals having a specified number of bits into protected code signals preferably having the same number of bits and preferably exhibiting a specified 0-bit/1-bit ratio, and a second code converter comprising a counter, a feedback shift register, and two keying devices for converting the 1-bits for transmission at two levels, such as potentials, amplitudes, or frequencies, different from the level at which the 0-bits are transmitted, to form a ternary code with the number of 1-bits transmitted at one level and the number of 1-bits transmitted at the other level exhibiting a constant ratio.

Telegraph receiving apparatus

Abstract: 1,123,416. Radio receiving systems; telegraphy. STANDARD TELEPHONES & CABLES Ltd. 19 Nov., 1965, No. 49261/65. Headings H4L and H4P. In an alternating-current telegraph receiver including two separate signal paths, the said paths are coupled to a common impedance by a hybrid circuit arrangement so arranged that substantially no power is transferred from either path to the other. As described, the output A of a first receiving channel of a radio diversity system is connected through a band pass filter 1 to a hybrid transformer 4, by which it is divided to feed a mixer 8 in a "mark" channel 33 and a similar mixer 9 in a "space" channel 35. Similarly, the output B of a second receiving channel is divided by a hybrid transformer 11 to feed a mixer 15 in a "mark" channel 34 and a similar mixer 16 in a "space" channel 36. A common local oscillator 17 is coupled by a hybrid transformer 19 to the mixers 8, 15 and a common local oscillator 18 is coupled by a hybrid transformer 24 to the mixers 9, 16. In the hybrid transformer 4, the value of the balancing resistor 7 is so chosen in relation to the input impedance associated with the primary winding 3 and the turns ratio between the secondary 5, 6 and the primary, that there is substantially no cross-coupling between the mixers 8 and 9. Similar considerations are applied to the other hybrid transformers 11, 19, 24. With a frequency shift keying system, the input carrier frequency may be 100 kc/s, with Œ0A1 kc/s shift, the oscillators 17, 18 being set, respectively, at 94A9 kc/s and 95A1 kc/s, so that the "mark" and "space" outputs are all at 5 kc/s. The arrangement may be extended for use in a frequency-shift diplex system, where four frequencies deviated from a carrier are used, or it may be adapted for on-off keying, when the oscillator 18 would be disabled. With a non-diversity system only one hybrid transformer, 4 or 11 would be used.

Diode keying system for electronic organ

Abstract: The keying networks between continuously running square wave tone signal sources and the sound output system of an electronic organ each consist of an isolating diode gate for each source, followed by the parallel combination of at least two keying diode gates of simplified circuitry which either gate-through the square wave signal without change in wave shape (for odd-orderharmonic tones) or gate-through and modify the wave-shape into sawtooths (for full harmonic tones). A keyed activating circuit for the isolating diode gate and the keying diode gates corresponding to a selected key may contain a single key switch connected to a source of direct current and a common R-C attack network for two adjacent footage keying diode gates as well as for the paralleled keying diode gates. A common coupler switch for coupling between keyboards is located between the direct current source and auxiliary key switches ganged respectively to the main key switches for a given manual, the auxiliary key switches being connected to a diode to isolate them from the main key switches in the coupled keyboard.

Microwave Moon relay communication at high digit rates

Abstract: An account of experiments demonstrating Moon relay communication at 800bit/s is given. Formulas and graphs are presented which enable the error probabilities for 2-level or more f.s.k. (frequency-shift keying) combined with frequency diversity to be calculated. Comparison is made between the calculated and experimental results. These are in good agreement.

Two-transmitter radio beacon

Abstract: A radio beacon generating an audio-modulated UHF signal has two transmitters keyed by the outputs of independent square-pulse generators. Each pulse generator works into an associated amplifier stage, an inversion of the output of the pulse generator feeding the first transmitter being also supplied to the amplifier stage of the second transmitter (in parallel with the output of the other pulse generator) whereby the complement of the keying signal of the first or master transmitter normally overrides the keying signal of the second or slave transmitter and the two transmitters operate at interleaved intervals. If the master transmitter should fail, the slave transmitter continues operating in the rhythm of its own keying signal.

Error Performance of Differential Phase-Shift Transmission over a Telephone Line

Abstract: This paper considers differential phase-shift transmission over a bandlimited channel with specified phase and amplitude characteristics. The problem treated is the prediction of feasible data rates and corresponding error rates over such channels. An expression is given for the probability of error. This expression takes into account intersymbol and interchannel interference when differential phase-shift keying (DPSK) modulation is used. A distortion index which is a measure of phase error is defined, and the concept of phase opening is used which parallels the concept of eye opening commonly employed in the amplitude-shift keying (ASK) modulation. The analytical methods are applied to illustrate the effects of various parameters on the performance of a high data rate transmission system over a telephone line. Results indicate that for a carefully equalized line, a single-tone system should be used, and that higher order phase alphabets are to be preferred as the bit rate increases.

Transistor-keyed circuit for transient-free frequency shift keying

Abstract: IN FREQUENCY-SHIFT KEYING A SIGNAL WITH A TRANSISTOR KEYING DEVICE, PHASE SHIFT AT THE INSTANT OF KEYING IS AVOIDED BY CONNECTING, IN PARALLEL WITH THE OSCILLATOR TANK CIRCUIT, A REACTANCE IN SERIES WITH A PARALLEL-CONNECTED RESISTORAND-UNITY-GAIN-AMPLIFIER COMBINATION SO THAT ENERGIZATION OF THE UNITY GAIN AMPLIFIER PREVENTS CURRENT FLOW THROUGH THE RESISTOR WITHOUT PHYSICALLY DISCONNECTING IT FROM THE CIRCUIT.

Multiplex Telemetry Modulation and Demodulation Methods

Abstract: There are a wide variety of modulation methods among the recently used telemetry systems. Characteristics and capabilities of some of these methods are briefly described. There is no generally accepted "best" method. Requirements for conservation of radio spectrum have a strong influence on the choice of modulation parameters. New Inter-Range Instrumentation Group (IRIG) modulation standards have been adopted. Some parameter variations within the new FM-FM standards are presented. The spectrum and data capacity of IRIG PCM-FM are discussed. Various forms of phase-shift keying (PSK) are described. Needs for increased data bandwidth have led to the development of single-sideband subcarriers, used as SSB-FM. Coded transmission with coherent demodulation can provide better carrier signal energy efficiency, but has been rarely used. Noncoherent orthogonal codes appear worthy of further exploitation, being almost as efficient as coherent orthogonal but simpler to produce and detect. Literature references are included for further study.

Error Performance of Quadrature Pilot Tone Phase-Shift Keying

Abstract: In this paper we exhibit the effect of the data sequence on the reconstruction of the reference (pilot) tone for a quadrature phase-shift keying (Q-PSK) system. This is a binary digital transmission system in which the phase of one quadrature component of the carrier tone is keyed, while the phase of the other component is unkeyed. The integration of several previous keying intervals provides a reference phase. A scheme of this type, called Kathryn, has been built by General Atronics Corporation. We find that the performance of a Q-PSK system is limited by self-noise unless certain message sequences can be avoided. It is concluded that a Q-PSK system can be used effectively only in a decision-directed mode which is also analyzed.

Digital Computer Simulation of a Frequency-Shift Keying System

Abstract: A digital computer simulation of a noise-free frequency-shift keying (FSK) data system is described. This system consists of a frequency modulator, a send and receive bandpass filter, a limiter, and a frequency demodulator. The simulation is used to study the performance of the system in terms of telegraph distortion for various filters and demodulators. The accumulated spectral density of the modulated Q 9S test signal is examined. The modeling of the system and the processing of the test signal are discussed.