Disclosed is a transcontinental communications network particularly designed for the very rapid transmission of digital data between subscribers throughout major areas of the United States. The network comprises a microwave trunkline extending from San Francisco downwardly through the center of the country and upwardly to Boston along which data may be transmitted at rates of 4800, 9600, and 14,400 bits per second and higher. Transmission along the trunkline is by phase modulation of a carrier in the 6 MHz and 11 MHz band. Time division multiplexing provides a minimum of 4,000 channels utilizing a relatively small bandwidth of the frequency spectrum. The trunklines are under the control of switching centers comprising regional and district offices which allocate channels and handle communications traffic through the network. A microwave cable or optical local distribution system connected to the basic trunkline provides a full duplex operation throughout the network and insures the rapid transmission of data completely throughout the network from one subscriber to another.

Data transmission network

A clock control system for a multiple channel electric power system includes a master clock circuit and control circuitry in each parallel connected channel. The channel control circuits are intially phase-locked to a master clock signal. If the master clock signal is out of a preselected frequency range, the individual channel control circuits are decoupled from the master clock signal and one of those circuits produces a backup clock signal. The control circuits in the remaining channels are then phase-locked with the backup clock signal to provide continued parallel system operation.

Master clock system for a parallel variable speed constant frequency power system

A circuit for tuning an electronically tuned radio receiver in which the tuning voltage for tuning the radio receiver is supplied to the positive input of a first differential amplifier having a high gain whose output is connected across a voltage responsive capacitive element for controlling the frequency of oscillation of a voltage controlled local oscillator. The output of this voltage controlled local oscillator is supplied to a linear frequency-to-voltage converter whose output is supplied to the negative input of the first differential amplifier to maintain the output of the local oscillator a linear function of the tuning voltage. The tuning voltage is also supplied to the positive input of a second differential amplifier whose output is supplied to the positive input of a third differential amplifier having a high gain. The output of this amplifier is connected across a voltage responsive capacitive element in a reference voltage controlled oscillator to control the frequency of oscillation thereof and across respective voltage responsive capacitive elements in the antenna and RF tuned circuits to control the tuned frequency thereof. The output of the reference voltage controlled oscillator is supplied to a linear frequencyto-voltage converter whose output is connected to the negative input of the third differential amplifier to maintain the frequency at which the reference voltage controlled oscillator, antenna and RF tuned circuits are tuned a linear function of the input voltage to the positive input of the third differential amplifier. A constant DC voltage is supplied to the negative input of the second differential amplifier to effect the tracking of the antenna and RF tuned circuits to the output of the voltage controlled local oscillator at a constant difference frequency equal to the IF frequency.

Bias voltage generator for the voltage-responsive tuning elements in an electronically tuned radio receiver

A circuit responsive to an input signal having an unspecified frequency for converting it to a predetermined and constant means frequency, and particularly suitable for incorporation in a modulation measuring instrument, comprises a sampling mixer controlled by a variable frequency oscillator for sampling the input signal to produce an intermediate signal. The mean frequency of the intermediate signal is then compared with a reference representing a predetermined frequency value whereby to produce an error signal, and means responsive to the error signal adjusts the frequency of the oscillator in such a direction as to tend to hold the mean value of the frequency of the intermediate signal at the predetermined frequency value while preserving therein variations in amplitude and/or frequency due to amplitude and/or frequency modulation.

Frequency control circuits such as for use in modulation measurement

A received RF signal is mixed with the output of a voltage-controlled local oscillator to provide an IF signal which is simultaneously passed to a frequency discriminator and a circulating memory. Control voltage for the oscillator is provided by an AFC unit which comprises an integrator receiving selected constant voltage inputs. During the search mode a search ramp is generated by the integrator. A flyback circuit causes the search voltage to repeat its traverse over a prescribed range. Bipolar video discriminator outputs above a predetermined threshold place the system in the lock mode and selectively gate two settable, constant voltage inputs to furnish a triangle wave integrator output centered on a voltage corresponding to the desired local oscillator frequency. The oscillator output is mixed with the stored IF to produce a replica of the input signal.

Search-lock system

A frequency synthesizer particularly suitable for VHF applications comprising a pair of variable frequency oscillators adapted to be simultaneously tuned in coarse frequency steps, one of the oscillators being phase locked to a frequency standard, and the second oscillator being controlled by a tunable frequency lock loop referenced to the first oscillator to provide the synthesized frequency output. The tunable frequency lock loop includes a balanced mixer coupled at the outputs of the two oscillators for producing a difference frequency, a frequency discriminator for providing a voltage signal proportional to this difference frequency, a continuously or discretely variable tuning voltage, and a difference amplifier which compares the discriminator output with a selected tuning voltage and provides a difference signal for fine tuning the second oscillator.

David J Blair

Papers

Wide range frequency synthesizer