Abstract: A radio transceiver includes means to switch from the transmit to the receive mode. The disclosed squelch circuit operates in the receive mode to mute and unmute the receiver at different received signal levels to prevent undesirable muting during signal fading conditions. The squelch also provides a means to mute the receiver for a sufficient period allowing switching transients to die out after the transceiver has been switched from the transmit to the receive mode.

Abstract: A resistor is inserted between the audio signal and the primary winding of a conventional modulating transformer used in an amplitude modulated transmitter. The value of the resistor is selected to limit the peak signals into the transformer thereby limiting the peak instantaneous index of modulation to less than 100 percent.A capacitor, coupled to the transformers secondary winding, forms a low pass filter with the impedance of the resistor as transformed by the turns ratio of the transformer. The resulting low pass filter attenuates undesired harmonics.

Abstract: A two-way FM radio transmitter-receiver operates on a single channel and automatically samples the channel during transmissions to sense the presence of a carrier wave. The transmitter is actuated by use of a transmit key which starts timing means to produce a time interval, and at the end of the time interval a sample generator is actuated for a very short time period to turn off the transmitter, disconnect the antenna from the transmitter, and connect the antenna to the receiver. A detector coupled to the squelch circuit of the receiver at the transmitting station detects the presence of a carrier wave on the channel, and the detector output produced in response to a carrier wave acts to hold the transmitter off and allow the receiver to reproduce the received wave. When the transmitter is turned off for the short time period, the absence of the carrier will cause the FM receiver at the receiving station to produce a burst of noise.

Abstract: A unique printer head employs a plurality of bimorph benders to drive a wire matrix. The benders are of the circular, high power type, having centrally located coupling washers. A housing supports the benders which are stackably mounted therein such that the washer openings form a central cavity which is aligned with an opening in the housing. Each wire couples to a corresponding bender to be ballistically driven thereby. The wires are routed through the central cavity and wire guides for actuation out the housing opening.Because of the high efficiency of the bimorph bender drivers, the improved printer head has reduced size and weight, while maintaining a high reliability.

Abstract: An inductor coil consisting of two cores enclosed by a single layer of wire is disclosed. The cores may be of the same or different permeability. The coils arranged in this configuration behave like two coils in series in which the relative values of inductance can be varied independently, thus the change in inductance depends only on the number of turns and the relative permeability of the cores. Decreased sensitivity, however, is obtained because of the increased area inside of the coil provided by the two cores side by side.

Abstract: An FM radio receiver with a discriminator having connected thereto a plurality of bandpass filters, each tuned to pass a different portion of the audio spectrum from the discriminator, and circuitry connected to the bandpass filters for selecting the filter with the lowest output signal which is an indication of the amplitude of the noise and, hence, the quality of the signal being received by the receiver.

Abstract: A mixer connected to receive a pilot signal from a suppressed carrier communications system and further connected to receive a signal from a crystal controlled oscillator with a plug-in crystal is disclosed. The output of the mixer is coupled through a very narrow bandpass filter tuned to pass only the converted pilot frequency. The output of the mixer develops a control signal which is coupled to a regulating input of variable gain amplifier means for regulating the gain of the amplifier means in direct proportion to changes in level of the pilot.

Abstract: The coupler inserts in an RF transmission line and produces a pair of DC signals whose level is representative of the magnitude of forward or reverse power flow therethrough.Power flow is sensed via a pair of non resonant loops, each of which is terminated and oriented such that AC signals, whose amplitudes correspond to the forward or reverse power flow magnitude, are produced. Since the RF signals produced by the loops are dependent on the RF power flow frequency, unique circuitry processes the RF signals and compensates for this frequency dependence whereby the processed AC signals are substantially frequency independent.Also disclosed are improved rectification circuitry, and a means to compensate the coupler against error due to thermal drift of coupler components.

Abstract: A controllable oscillator is maintained at a center frequency f.sub.o by the inventive system. The oscillator signal is directly coupled to one input of a diode detector via a first path, and is alternately coupled, at a clock signal rate, to the second detector input via second or third paths. The second path has a selected transfer characteristic such that when it passes the oscillator signal the diode detector output is at a null. The third path includes a resonator whereby the oscillator signal passed therethrough results in a null at the detector output only when the oscillator is tuned to f.sub.o. The diode detector output is then phase detected with the clock signal thus producing an output correction signal which, when integrated, is fed back to the oscillator for precise control thereof. Since the system correction is dependent solely on an AC signal, errors due to the DC characteristics of the components, e.g. the detector diodes, may be eliminated.

Abstract: A system for processing a digital information bit stream and generating a data bit stream. The processing includes convolutional burst error correction encoding which is capable of correcting burst errors of length 2B, where B is any positive integer. Inherent in such systems are the requirements of 2B and 5B zero level bits at the beginning, and end, respectively, of the data bit stream. The processing further includes encoding n sync bits at the beginning of the data bit stream.The improvement includes encoder apparatus for replacing the 2B zero bits with the n sync bits; and, decoder apparatus for detecting a threshold number of sync bits and, in response thereto, replacing each sync bit with a zero bit. This improvement significantly reduces the number of bits otherwise required in the data bit stream.

Abstract: A radio communication system of base stations, and a telephone system, are linked and controlled by a control center.

Abstract: An audio signal quality detector connected to receive an audio signal from the discriminator of a radio receiver and including an envelope detector connected to the output of the discriminator and supplying a signal indicative of the envelope of the audio to a resettable valley detector which stores a voltage indicative of the lowest valley applied thereto subsequent to a reset pulse and a sample and hold gate connected to the valley detector for sampling the voltage stored in the valley detector prior to periodic reset pulses applied to the valley detector. Circuitry is also included for inhibiting the operation of the sample and hold gate when there is no output from the valley detector.

Abstract: A directional power detector mounted between the power amplifier and antenna which supplies audio frequency output signals indicative of forward and reflected power, circuitry for summing and converting the output signals from the power detector means to a DC potential proportional to the magnitude thereof and a transistor connected in shunt at the input of the power amplifier and controlled by the DC potential for controlling the peak envelope power at the antenna.

Abstract: First and second batteries each connected in parallel with a load and a battery isolator connected between the first battery and the second battery and the load including a series pass transistor connected in series with the first battery and the load and circuitry for comparing the voltage across the load to the voltage across the first battery and turning off the series pass transistor when the voltage of the first battery drops below the voltage at the load plus a predetermined offset voltage, which offset voltage is developed by the battery isolator. The battery isolator operates like a diode isolation circuit having a near perfect diode therein.

Abstract: An improved receiver voting system is disclosed in which the lowest noise audio signal produced by a number of different radio receivers is selected and coupled to a monitoring speaker. Each receiver receives signals from a transmitter and produces either corresponding audio signals or squelch indicating status tones which are then transmitted to a voting (selecting) control center by telephone communication lines. The voting control center then selects the unsquelched receiver audio signal having the lowest noise level and couples this signal to a monitoring speaker.The voting center indicates which receiver is supplying the selected signal and therefore identifies the most favorable receiver to transmitter signal path. Parallel squelch circuits in each receiver provide for the initial selection of the strongest received signal while preventing the existence of an irratating "squelch tail.

Abstract: An audio derived AGC signal for controlling RF and/or IF amplifiers in the radio receiver wherein a first control signal is developed by a circuit having a relatively slow response time when the audio output signal is below a predetermined value and a second control signal is developed by a circuit having a relatively fast response time when the audio output signal is at or above the predetermined value. The control signals are developed across a storage capacitor and a circuit is connected thereto for quickly discharging the capacitor when no signal is being supplied from the audio circuit.

Abstract: A simple recyclable key and locking system for enabling a pay TV converter is disclosed. The key is a small tag such as might be attached to the room key of a hotel room and is to be turned in with the room key. The TV viewing key is inserted into a locking-unlocking unit which determines its validity, makes the appropriate connection in a pay TV converter to enable viewing, then cancels the validity of the key. When turned in, the key is easily examined as to whether or not it has been used, and, if so, it can be quickly revalidated for reuse. The key user is billed only if his viewing key has been used, or is not returned. In a residential situation, the viewing key would be purchased, then discarded after one use.

Abstract: A communication system of the type wherein a central station assigns a limited number of information channels to a requesting one of a plurality of remote stations is disclosed. The requesting station sends its identification signal along with the request signal to the central station on a signal channel. The central station classifies the requesting station in either a priority or a nonpriority queue. The priority queue corresponds to those stations which are continuing an on-going interchange, whereas the nonpriority queue contains those stations which wish to initiate an interchange. Stations are prioritized in the queues on a first-in/first-out basis.The central station constantly monitors the information channels and, as channels become available, assigns the channels first to stations in the prioirty queue, then to nonpriority queue stations.

Abstract: A harmonic filter failure detection apparatus for use in a single sideband radio transmitter is disclosed. A first directional coupler measures the power delivered to the harmonic filter and a second directional coupler measures the power passed through the harmonic filter. The power measurements of the first and second directional couplers are then compared in a latch type comparator circuit and a control signal output is developed which indicates whether or not the harmonic filter is operating properly. The control signal output is used to shut down the single sideband transmitter when a filter failure has been detected.

Abstract: Disclosed apparatus compensates for the parabolic temperature induced frequency drift characteristic of a surface acoustic wave tuned oscillator. The apparatus includes a pair of varactor diodes and a temperature sensitive voltage supply. The diodes are series connected and coupled in circuit with the oscillator to affect the frequency thereof. The voltage supply connects to the common connection of the diodes, for producing control voltages thereat.Each varactor diode is chosen to have a .delta. > 1; and the control voltage varies linearly with temperature. This results in a varactor diode capacitance versus temperature characteristic which is a continuous, true parabolic function providing precise compensation for the thermal drift of oscillator frequency.