Abstract: Information is conveyed from a transmitting site to a consuming location in an electric power system by varying the frequency of the power from the nominal standard generating frequency. The signaled variation in frequency is detected at a power consuming location and a frequency indicating signal is generated. Frequency deviations of predetermined magnitude for a predetermined time duration signal a selected range of power system load while different deviations for different times signal automatic remote control of certain predetermined loads or other functions.

Abstract: Information is conveyed from a generating site to a consuming location in an electric power system by varying the frequency of the power from the nominal standard generating frequency. The signaled variation in frequency is detected at a power controlling or consuming location and a frequency indicating signal is generated. Frequency deviations of predetermined magnitude for predetermined time duration signal a selected range of power system load while different deviations for different times signal automatic remote control of certain predetermined loads or other functions.

Abstract: The receiver of a facsimile system includes a modulator for generating a signal for transmission to a remote transmitting location to identify a characteristic of the receiver. The signal from the receiver varies between a first frequency which is contiguous with and immediately precedes a second frequency. By utilizing different first frequencies to characterize different types of receivers, the transmitter at the remote location is able to identify the type of receiver including, for example, the demodulating capabilities of the receiver.

Abstract: The receiver of a facsimile system includes a modulator for generating a signal for transmission to a remote transmitting location during predetermined intervals in the absence of received signals during those intervals. The signal from the receiver provides a periodic handshake function. The duration of the signal is short as compared with the duration of the predetermined intervals in which the received signals are absent.

Abstract: A facsimile transmitter comprises a rotatable drum and a sensor for detecting dark-light variations in a document mounted on the drum. A facsimile receiver comprises a rotatable drum and a writing stylus for reproducing dark-light variations on a copy medium mounted on the drum. Prior to transmission of modulated signals representing the dark-light variations in the document, synchronizing signals are transmitted from the transmitter to the receiver. The synchronizing signals comprise pulses of selected and controlled frequency duration and time lapse therebetween to signal the transmission mode. The various modes signaled include different and variable scanning rates, different frequency bandwidths and different forms of modulation.

Abstract: A facsimile transmitter detects dark-light variations in an illuminated document by means of a photodetector. After amplification, the output from the photodetector is applied to a threshold detector generating a multilevel digital signal. When the magnitude of the amplified photodetector signal is greater than one fixed threshold level, one level of the digital signal is generated. When the magnitude of the amplified photodetector signal is less than another fixed threshold level, another level of the digital signal is generated. When the magnitude of the amplified photodetector output lies between the two threshold levels, one level of the digital signal is generated when the peaked, amplified photodetector signal is greater than the unpeaked amplified photodetector signal and the other level of the digital signal is generated when the peaked amplified photodetector signal is less than the unpeaked, amplified photodetector signal.

Abstract: In a facsimile system, rotation of a transmitter drum carrying a document is synchronized with the rotation of a receiver drum carrying a copy medium. Synchronization of the rotating transmitter drum and the rotating receiver drum is assured by driving the transmitter drum from an AC power line and locking the receiver drum to the AC power line frequency once synchronization of the transmitter drum and the receiver drum have been achieved. In order to achieve initial synchronization, the drive for the receiver drum is initially locked to a source of controlled frequency until a predetermined angular position of the receiver drum relative to a predetermined angular position of the transmitter drum is attained. The receiver motor which is of the DC type is controlled in angular frequency after initial synchronization by generating a signal having a frequency phase locked to the AC power line frequency.

Abstract: Frequency modulated pulses representing dark/light variations on a document are applied to a frequency limiting circuit prior to synthesizing a low distortion sinewave voice band signal from the pulses. The frequency limiting circuit detects the frequency of the pulses and divides the frequency when the frequency exceeds a predetermined level. Detection of frequencies in excess of the predetermined level is achieved by a counter which counts clock pulses applied to the counter during each cycle of the frequency modulated pulses to determine the time between pulses and thus the frequency of the pulses. A gate only passes the pulses after a predetermined count has been reached.

Abstract: A frequency modulated facsimile signal is synthesized from a high frequency signal having a frequency which varies in response to dark/light variations on a document. The higher frequency signal which comprises pulses is coupled to a synthesizing network which includes a digital-to-analog converter for producing synthesized frequency modulated facsimile signals. Enabling circuitry is associated with the digital-to-analog converter which assures that the frequency modulated facsimile signal will not terminate or begin except at axis crossing times.

Abstract: A facsimile transmitter comprises a rotatable drum and a detector for detecting dark-light variations in a document mounted on the drum. A frequency modulator is coupled to the detector for generating frequency modulated transmission signals representing dark-light variations in the document. A sync generator, which generates synchronizing pulses coincident with juxtaposition between the detector and the document-holding clamp on the drum, is also coupled to the frequency modulator. The transmission mode, e.g. the choice of utilizing an internal stable frequency or external power line frequency synchronizing signal to synchronize the drive of the drum, is signaled by varying the length of the synchronizing pulse during the sync period preceding transmission of document information.

Abstract: Ancillary equipment including a facsimile transceiver is directly connected to a telephone network through a coupling arrangement. The coupling arrangement includes a transfer relay for transferring the primary communication path to the telephone network between a telephone station set and the ancillary equipment. The transfer between the telephone station set and the ancillary equipment is controlled by a sensor which electrically senses a change from the off-hook to the on-hook state of the telephone set. The transfer is also controlled in response to the state of the ancillary equipment. The coupling arrangement also limits the signal power level coupled into the telephone network from the ancillary equipment.

Abstract: In a facsimile system, rotation of a transmitter drum carrying a document is synchronized with the rotation of a receiver drum carrying a copy medium. Synchronization is achieved by rotating the transmitter drum at a substantially constant angular frequency while generating transmitter synchronizing pulses corresponding to that frequency and rotating the receiver drum at an initial angular frequency while generating receiver synchronizing pulses corresponding to the initial frequency where the initial frequency of the receiver drum differs substantially from the constant frequency of the transmitter drum. When partial coincidence between portions of a transmitter synchronizing pulse and the receiver drum synchronizing pulse is detected, the receiver drum is rotated at another frequency closer to the constant frequency of the transmitter drum.

Abstract: FM signals within a predetermined bandwidth representing light-dark variations in a document are transmitted over a communications network to a facsimile receiver. The FM signals are applied to differentiating and frequency doubling means so as to generate trigger signals with substantially equal amplitude and width for application to a single shot multivibrator. Reset means coupled directly to the input of the single shot multivibrator are responsive to the trigger pulses to reset the single shot multivibrator to the astable state when the frequency of the trigger pulses is sufficiently high that trigger pulses occur while the multivibrator is in a previously initiated astable state. An average DC voltage detector is connected to the output of the multivibrator such that the average DC voltage represents the ratio of the astable state duration to the stable state duration.

Abstract: A facsimile receiver which may be acoustically coupled to a telephone transmission line comprises a preamplifier for amplifying frequency modulated signals. The output of the preamplifier is coupled to a demodulator comprising a single shot multivibrator and an average DC voltage detector connected to the output of the multivibrator. The output of the average DC voltage detector is applied to a stylus driver which controls the marking of a copy medium by a stylus. A signal quality detector and an indicator are coupled to the output of the preamplifier to provide an operator with an indication of poor signal reception quality.

Abstract: A document/copy carrying drum of a facsimile transceiver is rotatably driven by a synchronous motor. The synchronous motor is connected as a load in series with a first transistor and a first power supply of one polarity. The synchronous motor is also connected in series with a second circuit and a second power supply of opposite polarity so as to apply DC voltages of opposite polarity during alternate conduction of the transistors. Conduction of the transistors is controlled by alternately applying a series of relatively low voltage pulses to the bases of the transistors through high frequency isolation transformers. The pulses are separated by a time interval less than the base storage time of the transistors so as to assure continuous conduction between the collector and emitter of a transistor while a series of pulses is applied to the base thereof.