Abstract: An improved automatic gain control (AGC) for a television transmission system comprising a transmitter for transmitting a TV signal via a transmission path to a receiver and having a certain bandwidth in which said transmitter includes a generator for generating a baseband TV signal which can be pre-emphasized, and a variable gain amplifier responsive to the baseband TV signal to produce an amplified baseband video signal. The AGC system comprises a band eliminating filter responsive to the baseband output signal to produce a control signal whose amplitude reflects the change in energy content of that portion of the TV output signal lying outside the allowed transmission bandwidth. The variable gain amplifier is responsive to the control signal to vary its gain substantially inversely as the out-of-band energy content varies. At the receiver a detector detects a component of the received TV signal which has known characteristics, usually constant, in the absence of the gain introduced at the transmitter.

Abstract: A digital AM broadcast transmitter features a plurality of stages that are controlled by a digital signal representing an audio modulating signal. At least some of the stages are cascade coupled together using transformers. This reduces the need for high turns ratios and allows most or all transformers to be identical.

Abstract: A signal transmission system, particularly for television, comprising a nonlinearity precorrection device having a principal channel and a subsidiary channel. The subsidiary channel comprises a nonlinearity product generator with two amplification channels, a linear channel and a nonlinear channel which enable nonlinearity products having a suitable phase to be extracted by the difference of their output signals. The principal channel comprises a circuit formed from two linear channels in parallel whose output signals are added together in an adder. The output signals of the subsidiary channel and the principal channel are added. This precorrection device enables automatic correction of the nonlinearity products to be set up.

Abstract: A radio transmitter has an output power control circuit including a power amplifier, a directional coupler coupled to the power amplifier, a detector of the forward power of the directional coupler, a generator of a difference voltage between the output voltage of the detector means and a reference voltage. A power regulator varys the output power of the power amplifier in response to the output of the difference voltage. The power applied from the power amplifier through the directional coupler to the detector is controlled by a control signal.The control circuit electrically varies the coupling coefficient of the directional coupler for attenuating the power applied from the directional coupler to the detector means to extend the controllable range of the transmitter output power.

Abstract: An automatic gain control (AGC) circuit arrangement is disclosed as including an AGC loop responsive to an input signal and operative to maintain an output signal at a desired mean level represented by a reference signal applied in the loop and also subjected to amplitude modulation by an AF signal. The circuit arrangement includes modulators outside the loop for changing the level of the input signal by amounts corresponding respectively to changes in level represented by changes in the AF signal and by changes in the reference signal. Therefore, the level of the input signal as received by the AGC loop is at least approximately at the right value and its gain is held substantially constant even when the level of the required output signal for a given input signal changes. Therefore, variations of bandwidth resulting from gain variations are avoided.

Abstract: A transmitter control system for transmitters having means for selectively switching one channel to another in the multiple channels and means for controlling the transmitter output so as to deactivate, activate and reduce the transmitter output. The system comprises comparator means for comparing a start signal from the transmitter output control means with a detected signal of the transmitter output, the output of the comparator means being adapted to selectively drive at least one of the channel switching means for switching channels and a transmitter power reduction control circuit included in the transmitter output control means upon occurrence of a detected signal of the transmitter output indicative of a failure of the transmitter.

Abstract: An intermodulation distortion limiter controls the ratio of average power to peak envelope power in the output of a linear power amplifier and this protects against excess non-linearity by reducing the drive power when the ratio exceeds a similar ratio associated with the incoming RF signal.

Abstract: A teaching apparatus including a transmitter portion, a receiver portion and a prompter portion, each of the portions being disposed in a separate self-contained unit, the transmitter portion being adapted to be worn on the head and including a peripheral band portion and a top connecting portion extending in an arcuate path between opposing sides of the peripheral band, a microphone disposed on the under side of the connecting portion intermediate the ends thereof for contact with the head, an antenna associated with the peripheral band portion, citizen's band transmitter mechanism located on the connecting portion, power supply member connected to the transmitter member, voice activatible actuating member connected to the transmitter member; the receiver portion being adapted to be worn on the head and including a peripheral band portion, transducer member disposed on the inside of the peripheral band portion, citizen's band receiver member connected to the transducer member, power supply member connected t

Abstract: A modulating signal is applied to an analog-to-digital converter which addresses a read-only memory phase look-up table. The read-only memory phase look-up table output is applied to a polarity generator. The polarity generator output and output from a phase accumulator are input to a phase adder. The phase adder output is applied to the input of a sine look-up read-only memory whose output is applied to a digital-to-analog converter and low-pass filtered to produce an amplitude-modulated carrier signal. The invention thereby digitally amplitude modulates a carrier signal in the phase domain without any multiplication being required.

Abstract: The transceiver according to the invention is controlled by an automatic alternation device in order to permit transmission solely when voice signals are to be transmitted and when the receiver does not receive such signals. On transmission, the transmitter supplies constant amplitude-modulated, high frequency signals during voice activity periods and supplies nothing outside these periods. On reception, a detector for detecting the rapid amplitude transitions of the received signals and a logic circuit control the switching off of an electronic switch during the voice activity periods, so that the output of the receiver only supplies voice signals. The gain of the receiver amplifier is controlled by an automatic control loop. The value of the time constant of this loop is controlled so as to be low during the voice activity periods and high outside these periods.

Abstract: In a single-voice-signal-per-carrier communications system, means are provided for limiting the intermodulation distortion in a common amplifier of a plurality of talkspurt voice signals. Separate carrier waves and voice signals are applied to respective modulators. The voice-operated-switch signals associated with respective voice signals are applied through a limiter circuit to the respective modulators. The limiter circuit limits the number of modulators generating talkspurt signals at any instant to a number which avoids intermodulation distortion.

Abstract: A system for reducing noise transients in electrical carrier signals, carried simultaneously over two separate channels, that are identical in their program component but differ in transient noise content, comprising means for comparing noise transients in the respective channels and for transmitting the electrical sum of the two channels unless the noise transients of the two channels differ by more than a selectable threshold amount, in which case only the carrier signal with the lesser noise transient is transmitted.

Abstract: Television broadcast transmitters are often operated at remote sites and must be remotely controlled. The transmitters often include exciters driving high-power amplifiers. The exciters and high-power amplifiers produce incidental phase modulation of the broadcast signals. An exciter for generating modulated carrier signals at a television video carrier frequency may include compensation for incidental phase modulation in the exciter itself and in the following amplifiers. Such an exciter includes a first modulator for modulating video onto an IF carrier, which is coupled through a power splitter to a second modulator. The second modulator is switched at a frequency equal to the sum of the video and intermediate frequencies to produce the desired modulated carrier. The output of the power divider is coupled to an envelope detector which reconstitutes the video.

Abstract: An automatic modulation control in a transmitter, comprising an alternating modulation signal source, a modulation signal amplifier, a carrier generator, a modulator for modulating the carrier signal as a function of the output of the modulation signal amplifier, a threshold detector coupled in a direct current manner to the output of the modulation signal amplifier for threshold detecting the modulation signal output, a smoothing circuit for smoothing the threshold detected output, an amplifier for the threshold detected and smoothed output, and a control circuit for controlling the input of the modulation signal to the modulation signal amplifier as a function of the output of the threshold detected output amplifier.

Abstract: A method and apparatus for suppressing carrier leakage components in a system for modulating a carrier with a selected signal wherein the carrier and a quadrature component of the carrier are weighted and summed with the modulated carrier to produce a component substantially equal and opposite in phase to the leakage component so that the summing substantially cancels or suppresses the leakage component.

Abstract: A mobile data terminal system is capable of voice or microprocessor controlled data transmission over a keyed transmitter. The improved timer apparatus disables further transmission if the transmission duration or the average duty cycle over a predetermined time period of repeated transmitter keying exceed predetermined limits. Where the disable mode resulted from a microprocessor fault, the transmitter continues to be disabled until the microprocessor is reset.

Abstract: The feedback controlled modulation system comprises an extended range, gain controlled detector system disposed in a first feedback loop coupled between the output and input of an amplifier having a non-linear input-output characteristic; a gain controlled reference signal source coupled to the output of the detector system to provide a difference signal in the first feedback loop; and a gain controlling pulse generator coupled to the source and the detector system to simultaneously control the gain of the source and the gain of the detector system to control the shape of the difference signal so as to linearize the non-linear characteristic without loss of loop stability and without causing amplitude distortion in the first feedback loop.

Abstract: A radio transmission system is disclosed having a base station with a plurality of spaced radio transmitters in which an information signal is simultaneously transmitted on the same carrier frequency channel from all the transmitters. Each information signal is transmitted at least twice while the relative transmission powers of the transmitters are varied between one transmission of an information signal and a subsequent retransmission of the same information signal.