Abstract: A microwave amplitude modulation system maintains constant amplitude attenuation at very high modulation rates over a broad range of microwave frequencies in response to voltage driving signals derived from modulation signals. In the system, the video input of a shunt-type PIN diode microwave amplitude modulation system is driven by a logarithmic voltage amplifier circuit which receives the modulation signals as an input.

Abstract: In the case of a method for the generation of an amplitude-modulated ISB transmission signal from different AF signal (NF1,2), the signal vectors are split into signal components (x1,y1 and x2,y2, respectively), components sums (X,Y) are formed from the signal components and an amplitude signal (A(t)) and a harmonic phase signal are derived from the component sums. Amplitude signal and phase signal are then further processed separately and combined at the single transmitting tube (43) by combined amplitude modulation and phase modulation into the final transmission signal.

Abstract: An RF amplitude modulated amplifier system is presented incorporating a plurality of RF amplifiers which are compensated for unwanted phase modulation. The system includes a common RF driver for supplying a common RF driver signal. A plurality of actuatable RF amplifiers are provided with each having an input circuit for receiving the common RF drive signal. Each amplifier has a fully on condition for amplifying the common drive signal to provide an amplified RF signal, and a fully off condition. Each of these RF amplifiers exhibits a characteristic in that its input circuit has an input impedance which is greater when fully on than that when fully off, thereby tending to present unwanted phase modulation of the plurality of RF amplifiers. One or more of the RF amplifiers are selectively turned fully on in dependence upon the magnitude of an input signal.

Abstract: A synchronous transmission system that improves reception in areas where the main and the satellite signal create significant self interference. At least one of the synchronous transmitters is phase modulated in accordance with a selected modulation function which varies at a sub sonic rate.

Abstract: An RF-AM transmitter of the type including a power pulse amplifier driving an RF amplifier with a modulating voltage via a low pass filter includes a pulse width modulator for deriving variable frequency pulses having a frequency that is a direct function of an RMS like function of the amplitude and frequency of an information source; the width of the pulses is determined by the instantaneous amplitude of the information signal source. The pulse width modulator includes a constant amplitude, variable frequency triangular wave voltage controlled oscillator responsive to a DC signal representing the frequency and amplitude of the information source. In response to amplitude crossovers between the variable frequency triangular wave and the information source, transitions in the pulse width modulated wave are derived.

Abstract: An amplitude modulator for mixing multifrequency signals characterized in that there are combined a mixer for producing a mixed signal by mixing not less than two alternating current signals with different frequency and a signal generator for the modulator to modulate the mixed signal by applying modulation signal to the mixed signal. According to the present invention, the device can be simplified and miniaturized in comparison with the conventional one since the mixer and amplitude modulator are incorporated in the present invention, whereby reliability of the device is greatly improved.

Abstract: In an AM broadcast transmitter having a switching amplifier as main modulator (12), an additional modulator (18) is used in the radio frequency circuit in order to achieve a steady 100% modulation at the modulation minima, with the aid of which additional modulator the carrier signal is also modulated at the modulation minima. The LF signal needed for controlling the additional modulator (18) passes through a delay circuit (16) and a correction circuit (17).

Abstract: A radio frequency transmitter, amplitude modulated, having a single tuner that tunes the frequency oscillator, the isolating filter and the antenna impedance, all at the same time. The transmitter includes a tunable carrier generator for generating a carrier signal of a desired frequency, and a carrier isolator for filtering the carrier signal so as to ensure a clean, isolated carrier signal. A power amplifier is included for amplifying the signal from the carrier isolator. The power amplifier has a certain output impedance. An antenna is connected for transmitting the amplified signal from the power amplifier. The antenna also has a certain impedance. The transmitter further includes an impedance matching device connected between the antenna and the power amplifier for matching the antenna impedance and the power amplifier impedance. Finally, a single control knob is provided for simultaneously controlling the tunable carrier generator, the carrier isolator and the impedance matching device.

Abstract: A digital amplitude modulator for use in transmitting information signals in the context of AM audio and AM video. The amplitude modulator/transmitter basically consists of a predetermined number of quadrature hybrid power devices configured as combiners and arranged in cascade so that the output of one combiner becomes one of the inputs of its adjacent combiner. An analog signal source such as a microphone or a video generator, produces an analog signal that passes through an analog-to-digital converter. The output of the A/D converter appears on datelines. The data consists of four-bit words. However, it is contemplated that in order to improve the quality of the signals being transmitted, 12- or 16-bit words or any arbitrary n are employed. Each of the bits from the least significant bit (LSB) to the most significant bit (MSB) is fed into a gate. In turn, each of the gates has its output connected to one of the input ports of one of the combiners.

Abstract: The present invention relates to a device for use in an amplitude modulated RF transmitter. The device protects power transistors located in the RF transmitter particularly in the modulator and power amplifier portions of the transmitter. The device is comprised of a capacitor unit which is adpated to be charged in a first direction; a detector which detects an audio modulating signal; and a discharge unit which is connected to both the capacitor unit and the detector which selectively discharges the capacitor unit when the value of the audio modulating signal reaches a first preset level for a preset time duration during a portion of the audio modulating signal which causes positive modulation of the RF transmitter. The device also comprises a switch unit connected to the capacitor unit and which is activated when the capacitor unit discharges to a predetermined level. The switch unit is operable to remove, when activated, the audio modulating signal from the power transistors.

Abstract: An electrical signalling apparatus including a transmitter and receiver connected to the same electrical power distribution network wherein a signal generated by the transmitter is used to control apparatus connected to the receiver. The system uses a pair of amplitude-modulated low frequency signals as the control signals that react with the receiver to control apparatus connected thereto. The transmitter has an oscillator modulated by twin tuning forks and provides a signal for a period of, for example 10 seconds, determined by a time-delay relay. The receiver has a demodulator followed by two filters connected to integrators. As soon as the integrated signals reach a predetermined value, a control signal is transmitted to the output. This apparatus provides a communication system which is virtually insensitive to interferences on the distribution network and operates perfectly with weak signals.

Abstract: An RF-AM transmitter includes a pulse amplifier responsive to a pulse width modulated (PWM) signal derived in response to an information signal. A low pass filter converts pulses derived by the power amplifier into a variable amplitude signal that is DC coupled to a power supply for an RF amplifier. An amplifier system including the pulse and RF amplifiers has stray capacitance coupled to a modulator which derives the PWM signal; the stray capacitance lengthens narrow modulator output pulses so they are excessively long. The amplitude of only the narrow pulses is reduced by a resistor-capacitor timing circuit in series with a switch to substantially preserve the narrow pulse area. The switch provides a low impedance path from the timing circuit to a reference potential terminal when current initially flows in the circuit during pulse transitions and throughout the length of each of the short duration pulses.

Abstract: A digitally operating switching amplifier for direct and alternating voltage that is suitable as a modulation amplifier for radio transmitters with anode modulation. The power portion of the amplifier consists of cascade-connected, controllable, peak current-limited partial voltage sources that are connected via a low-pass filter to a load resistor, which is the high-frequency output stage in a radio transmitter. The control of peak current-limited partial voltage sources, some of which present differing voltage values, is effected in such a manner that a high degree of efficiency is attained and that distortions of the modulation signal are small.

Abstract: A switching amplifier, in particular for generating a modulated anode voltage for a high-frequency, high-power AM transmitter, includes a number of switchable voltage sources. The switchable voltage sources in a first portion of the amplifier provide small-scale gradations, which can be combined in any sequence. The switchable voltage sources in a second portion of the amplifier provide large voltage leaps of constant magnitude, which are combined in sequence.

Abstract: An AM signal transmitter for generating an amplitude modulated carrier comprises a voltage-increasing stage and a power-increasing stage. The voltage-increasing stage includes a pulse width modulator, responsive to an input modulation signal, for producing a pair of high frequency pulse trains which are modulated in width in a complementary fashion. The pair of pulse trains are respectfully fed to a pair of switching and amplifying elements arranged in push-pull fashion. The output of the switching and amplifying elements is processed through a low pass filter to eliminate high frequency components, and is stepped up in voltage by processing through a voltage step-up transformer. The output of the voltage step-up transformer is then fed to the power stage of the AM signal transmitter, which include a power amplifier. Both the power amplifier and the switching and amplifying elements can be powered from a single power source. Other embodiments of the invention can be realized.

Abstract: A broadcast signal transmitter utilizes a klystron and a transmitter amplifier (10) operating in a pulsed mode. Two feedback loops are provided for controlling the output of the amplifier (10). A first feedback loop includes a control circuit (14) for providing automatic gain control of the black level of a vision signal to be transmitted while the second feedback loop includes a further control circuit (18) for improving the linearity of the transmitter. The first feedback loop output control signal at line rate while the second feedback loop output signals at first rate, both being operative during the period when an insertion test signal (I.T.S.) is supplied to the transmitter.

Abstract: An amplitude modulator having first and second differential amplifiers which are commonly supplied with an amplitude modulated carrier signal and a third differential amplifier which is connected to the emitter current path of the first differential amplifier, wherein the third differential amplifier is supplied with a video signal for modulation through a limiter and a current value of a current source connected to the third differential amplifier is adjusted to thereby adjust a modulation degree of an amplitude modulated video signal derived from the first and second differential amplifiers so that a white level of an input video signal can be positively prevented from being deteriorated.

Abstract: A method for controlling the carrier of an amplitude-modulated transmitter, wherein a saving in carrier power with simultaneous minimum dynamic distortions is achieved by digitizing the useful signal and digitally processing all control signals. The circuit for carrying out the method contains a digital computing circuit which calculates from the digital amplitude values of the useful signal a carrier-control value which controls the carrier level via a digital switching amplifier.

Abstract: An amplitude-modulated transmitter wherein the carrier value (T) is controlled in accordance with an improved HAPUG (controlled-carrier) method. Increased energy saving with simultaneous increase of the signal-to-noise ratio at the reception site is achieved by controlling the carrier along a static characteristic (SK) which begins, with a decreasing modulation level (P), with a residual carrier value (R), drops with increasing modulation levels to a minimum carrier value (T.sub.min) and passes into an ideal carrier-control characteristic only above a first level value (P.sub.1). Additional dynamic control results in a reduction in cross-over distortions.

Abstract: A polar loop transmitter having particular, but not exclusive, application in VHF single-sideband radio systems.In order to avoid having to match the amplitude detectors used in known polar loop transmitters, it is proposed as an alternative to provide a subtracting circuit which produces a difference signal from between the low level input signal and the attenuated output signal. The difference signal is amplitude demodulated in a mixer and the demodulated signal is used as a control signal for the amplitude modulator.First and second limiting amplifiers are used to derive the carrier signals from the input and output signals. The outputs of the limiting amplifiers are applied to a phase sensitive detector formed by another mixer whose output is used as a correction signal for a voltage controlled oscillator coupled to the amplitude modulator. The output of the first limiting amplifier is also used as the local oscillator signal for the amplitude demodulator.

Abstract: An apparatus and a method modulate a carrier signal so that the resultant modulated signal varies between a value substantially equal to the quiescent level of the carrier signal and peak values up to several hundred percent of the quiescent level of the carrier signal. The apparatus includes an electrical circuit for adjusting the modulating signal so that it is clamped at a reference value to prevent overmodulation. The clamped signal controls a variable resistance mechanism which forms a part of the gain determining portion of a modulator circuit including an amplifier. The amplifier modulates the carrier signal in accordance with the gain determined by the variable resistance. The variable resistance is controlled by the clamped signal so that it causes the gain of the amplifier circuit to vary between approximately one and a value greater than one.

Abstract: A phase modulator includes a digital frequency word generator, an adder and a register arranged to generate recurrent digital sawtooth signals at a carrier rate. A second digital adder is coupled to receive the sawtooth signals and also receives digital information signals. The adder produces recurrent digital sawtooth signals phase-modulated by the information signal. A pair of adders receive the digital sawtooth signals and mutually sign-reversed digital information signals to produce a pair of oppositely phase-modulated constant-amplitude signals in a pair of channels. A sine memory is addressed by the phase-modulated digital sawtooth signals to produce phase-modulated sinusoidal-representative digital signals. The digital signals are then converted to analog signals. Since the two channels contain signals which are phase-modulated but not amplitude-modulated, the signals may be amplified by nonlinear amplifiers.

Abstract: An amplitude modulator (10) is disclosed which generates an amplitude modulated carrier signal by selectively combining varying numbers of other carrier signals. A circuit (20) is included which provides plural carrier signals of like frequency and phase where the number of carrier signals being provided is dependent upon the level of an input signal. A combiner circuit (22) combines the plural carrier signals to thereby provide a combined signal which is the desired amplitude modulated carrier signal. In one embodiment (FIG. 3) the carrier signals which are combined are all equal in amplitude. In another embodiment (FIG. 4) the amplitudes of some of the carrier signals are weighted in a binary progression. In yet another embodiment (FIG. 9) the carrier signals are all frequency modulated whereby the output signal has both a varying frequency and amplitude.

Abstract: A power switching amplifier for digital power amplification of an analog input signal, wherein the input signal range is subdivided into a plurality of equal voltage steps and a number, corresponding to the number of voltage steps, of switching stages is driven and their direct-voltage sources are connected in series. The association between the voltage steps and the switching stages is variable, such that all switching stages are uniformly loaded and the switching frequencies are reduced.

Abstract: An amplitude modulator is disclosed which has first and second differential pairs of transistors whose bases are supplied with a carrier signal, and a third differential pair of transistors whose collectors are respectively connected to the common emitters of the first and second differential pairs of transistors and of which one transistor is supplied at a base with a modulating signal. The emitters of the first differential pair of transistors are connected together through corresponding resistors. The collectors of two transistors which are included in the first and second differential pair of transistors and of which the bases are connected together and further connected to a load resistor.

Abstract: A system and method for amplitude modulating a carrier signal with an audio or other information input signal relies on multivibrators and comparators initiating a logic controlled processing technique for providing two sinusoids, each a fundamental frequency waveform, the two having a mutual phase relationship defined by intermediate processing steps such that they differ in phase from 0 to 180 electrical degrees. The comparators output first resultant pulses when the carrier signal is greater than the amplitude of the audio or other information input signal. The first resultant pulses are input to a logic processing network to trigger multivibrators which output overlapping 180.degree. wide pulses, respective phase shifted resultant signal waveforms being formed from the respective comparator outputs.

Abstract: Modulation of a carrier signal using both amplitude and angle modulation increases the information capacity of transmission without increasing bandwidth. Complex zeros in an amplitude modulating signal are detected and a conjugation function dependent on the time of occurrence and imaginary root values of the zeros is generated. The conjugation function is inverted or not inverted in accordance with a binary data signal and used to control the frequency of an oscillator whose output is an angle modulated carrier signal which is then amplitude modulated. On reception the amplitude modulating signal is recovered by an envelope detector and the data signal by a phase locked loop.

Abstract: A rectifier, preferably a bridge rectifier, is connected in series between a radio frequency (RF) signal generator and audio signal generator, and an antenna included in an RF signal transmitting circuit for rectifying the signal generated by the transmitting circuit before transmission. In the case of an amplitude modulation (AM) transmitting circuit, relatively low percentage modulation causes the rectifier to operate in a linear range and results in relative intensification of the power in the sidebands of the AM signal, whereby the ratio of the sideband power to the carrier power is increased which means that a relatively greater amount of power is applied to transmission of the message-bearing sidebands as compared to the carrier than in conventional AM transmitting circuits.

Abstract: Improved radio transmitter modulation control circuitry is described which significantly increases the average power of the modulating signal, resulting in enhanced audio signal quality since the signal-to-noise ratio is likewise increased. The inventive modulation control circuitry includes a microphone 110, audio amplifier 120, splatter filter 130, modulator 150, potentiometer 140, oscillator and transmitter 180, and antenna 190. The audio amplifier 120 further includes an operational amplifier 160 having an input resistor 162 coupled via capacitor 168 to microphone 110, a phase-lag filter 170 coupled to the output of the operational amplifier 160, and a feedback resistor 161 coupled between the filter 170 and the input resistor 162. When driven into amplitude limiting, the phase and amplitude of harmonic signals from the operational amplifier 160 are altered by phase-lag filter 170 to produce a waveform similar to that shown in FIG. 2.

Abstract: A polar loop transmitter in which a negative feedback bias adjusting system is provided to control the bias voltage applied to a differential amplifier which supplies the input envelope information to an amplitude modulator, so that the R.F. modulated output goes to zero for a zero in the input.The envelope information negative feedback bias adjusting system modifies a predetermined bias voltage supplied by a potentiometer by sampling and holding the peak value of negative spikes occurring in the output of the differential amplifier and using the held value as a negative feedback voltage to the differential amplifier.

Abstract: To permit mass-production of coders selectively usable in various types of transmitter installations, and regardless of whether designed for stereophonic or monophonic transmission, in which a subcarrier of non-audible frequency (57 kHz) is radiated, amplitude modulated by separate recognition signals characterizing intelligence information (AR, or announcement recognition) and a specific transmitter (region or radio station recognition, RR), a memory element (36) such as a PROM is provided, connected to a selector switch, the memory element having stored therein data representative of(1) frequency of amplitude modulation of the subcarrier of the announcement recognition (AR) signal;(2) frequency of amplitude modulation of the radio station recognition (RR) signal;(3) degree of modulation by the (AR) signal;(4) degree of modulation by the (RR) signal, and,preferably, data to provide a visual indication of a respective frequency channel and modulation degree, the memory element (36) being programmed for select

Abstract: A method for amplifying electric signals, an amplifier circuit and application of this amplifier circuit as the modulator stage of a subsequent amplifier, employing a variable anode voltage for the purpose of improving the efficiency of amplifiers and particularly of high-power modulation amplifiers which are used, for example, in broadcast transmitters for the amplitude modulation of the radio-frequency output stage. From the modulation signal to be amplified, a control signal is derived in a control stage, this control signal being associated with the amplitude of the envelope of this modulation signal and being used for controlling the output voltage of a modulator/rectifier. The control signal is caused to follow the modulation signal within a presettable response time.

Abstract: Signal processing circuitry, preferably for use in multiplying two input signals, one at RF frequency and one at baseband frequency, which includes at least a basic four branch bridge circuit having a diode connected in each branch in a generally symmetrical four branch circuit configuration using a single bias supply and including a trimming resistor in at least one branch for controlling the current through the diodes in such branch so that the characteristics of the diodes in all branches can be matched over substantially the complete range of control current values therefor.

Abstract: An amplifier (FIGS. 1-3) is disclosed for amplifying an amplitude and frequency varying input signal. The amplifier includes a circuit (24, 100) responsive to the input signal to provide a digital representation thereof. In addition, a plurality of signal sources (30-36) are provided which each provide an associated signal. Another circuit (38-52) combines selected ones of the associated signals in accordance with the digital representation to provide a first combined signal having substantially the same waveform as, but of greater amplitude than the input signal.In several embodiments, a circuit (74, 76-78) provides an error signal in accordance with the difference between the desired and actual forms of the first signal. This error signal is combined with the first combined signal to derive an error corrected signal.

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: Signal processing circuitry, preferably for use in multiplying two input signals, one at RF frequency and one at base-band frequency, which includes a pair of PIN diodes connected in a generally symmetrical circuit configuration using a single bias supply and including a trimming resistor for controlling the current through a selected one of the diodes so that the characteristics of both diodes can be matched over substantially the complete range of control current values therefor. Further, the circuit configuration permits the use of an easy and effective technique for compensating for temperature changes of the circuit during operation.

Abstract: An amplifier circuit incorporating a valve or vacuum tube in the grounded grid configuration is disclosed. The anode D.C. potential is greater than the cathode D.C. potential which is in turn greater than the grid D.C. potential. The cathode is switched at an R.F. rate to a further D.C. potential below that of the grid. Preferably the grid potential substantially cuts off cathode current flow with the switch open. The amplifier finds particular application as an output amplifier in an A.M. R.F. transmitter with the modulation being provided by high level anode modulation. The tube or valve can be a triode, tetrode, or pentode.

Abstract: A method and apparatus for amplitude modulating a carrier signal with an audio or information input signal utilizes an arcsine generator to cause the envelope of the carrier to follow the input signal. The invention stems from the realization that if rectangular pulses of bipolar amplitude are symmetrically centered about 0 and .pi. radians of the carrier signal, the harmonic content can be expressed as a function of the angle of the rectangular pulses. This concept is realized by producing two opposite phase carrier signals which are compared with the modulation input signal to form two opposite phase rectangular pulse signals whose pulse widths are a function of the modulation input signal. Alternate phase pulses are extracted from these two rectangular pulse signals by two NOR gates, and the extracted pulses are combined and filtered to obtain an amplitude modulated output signal.

Abstract: A waveform capable of jamming some or all of the channels of a multiple channel receiver is developed by a multi-tone jammer that uses a digital counter and a digital/analog converter to generate a ramp voltage for a voltage controlled oscillator (VCO). The output of the VCO is modulated by a pin diode attenuator. The attenuator is controlled by a pattern generator synchronized with the digital counter to blank the retrace and any portion of the sweep to provide a partial band tone jamming spectrum. The digital counter is driven by a MHz reference signal generator and the sweep repetition rate is greater than the circuit bandwidth.

Abstract: A modulator receiving an analog input signal and a switching signal for providing an amplitude modulated output signal. The modulator includes a differential input amplifier coupled to a multiplier wherein the analog input signal is commutated through a load resistor by the switching signals that are supplied to the multiplier. A gating circuit is coupled to the multiplier whereby the analog input signal is commutated to a feedback circuit coupled between the gating circuit and the second input of the differential input amplifier. The feedback circuit produces an output for adjusting the bias potential at the second input of the differential input amplifier to equalize the differential output currents therefrom when the analog input signal is set to a nominal zero level and the gating circuit is activated.

Abstract: A radio frequency oscillator-modulator for use in a video game includes an oscillator circuit, formed from a first differentially connected, emitter-coupled transistor pair having base/collector cross-coupling, that is dc coupled to the differential inputs of a second differentially connected, emitter-coupled transistor pair that forms the modulator circuit. The modulation signal is applied through a resistance to the connected emitters of the modulator circuit to vary the drive current thereof. The radio frequency oscillator-modulator includes bias circuitry that establishes a low level of operation that provides for great linearity and low R.F. radiation.

Abstract: An AM broadcast transmitter uses a PWM modulator that requires a pulse width filter. It has been found that the filter load varies over the modulation cycle resulting in distortion. To overcome this problem, a varying voltage is applied to an RF driver stage during portions of the modulation cycle.

Abstract: An AM transmitter includes an RF signal generator and a switching-type RF signal amplifier. The RF amplifier output depends upon the energizing voltage applied thereacross, so it acts as a modulator. The energizing voltage is produced by a high-power audio amplifier which includes a pulse-width modulator driving a high-power audio switch. The switch terminals are coupled in series with an audio-frequency filter, energizing terminals of the RF amplifier and a source of direct energizing potential, for varying the voltage across the RF amplifier at an audio rate in response to the duty cycle of the width-modulated pulses for audio modulating the RF carrier. In order to reduce modulation distortion at low duty cycles resulting from the finite turn-on and turn-off time of the audio switch, an offset voltage generator is coupled to the filter by a diode. Energy stored in inductive components of the filter cause a voltage pulse during each turn-off of the audio switch.

Abstract: A high power amplitude modulated audio frequency transmitter having a Twin-T low frequency oscillator, a tickler coil high frequency oscillator, a switching regulator and a switching amplifier. The Twin-T low frequency oscillator produces a sine wave modulating signal which is fed to the switching regulator. The tickler coil high frequency oscillator produces a carrier signal which is fed to the input end of the switching amplifier. The output signal of the switching regulator is fed to the output end of the switching amplifier so that a sine wave modulated signal is developed on the output of the switching amplifier.

Abstract: Audio processing equipment for introducing additional asymmetry so as to provide increased fullness of modulation of associated transmitters. Audio waveshapes are altered so as to accentuate the positive going portions of the waveshape. The alteration of the waveshape is typically such that the waveshape will produce positive going modulation of approximately 125% when the negative going modulation is approximately 100%.

Abstract: A radio communications system for aircraft, particularly useful at UHF frequencies and in aircraft travelling at high speed and low level where rapid phase and amplitude fluctuations degrade intelligible speech transmission. The system comprises a transmitter in a first aircraft, the transmitter including an upshift frequency translator for transferring the frequency band of an input signal from a microphone to a higher band, and further including an amplitude modulator for modulating the frequency translated signals; and a receiver in a second aircraft arranged to receive and demodulate the transmitted signals, the receiver including a high pass filter for removing noise from the demodulated signal, and a downshift frequency translator for transferring the frequency band of the filter output to a lower band.

Abstract: In a high efficiency amplitude modulation circuit. A pulse width modulation switch is arranged with a low pass filter to attentuate switching frequencies of the switch. A diode is connected in parallel with the input terminals of the low pass filter which diode provides a current discharge path for the filter while the switch is non-conductive. A further filter is also connected in parallel with the input terminals of the low pass filter, this further filter being arranged to provide cancellation of the input susceptance of the low pass filter over at least part of its pass band. The two filters in combination are such as to present a constant input conductance over at least part of the pass band of the low pass filter.

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: An amplitude modulation circuit for a transmitter has an automatic level controlled circuit (ALC circuit), including in its negative feedback loop a series circuit of a high-pass filter, a rectifier circuit and an eliminator circuit, for modulation degree suppression, thereby avoiding overmodulation. The high-pass filter is so designed that the negative feedback signal level for modulation degree suppression of the ALC circuit is raised as the audio-signal frequency supplied to the transmitter increases. In the modulation circuit having such ALC circuit, a sufficiently high mean modulation degree may be obtained without encountering overmodulation if the main spectrum components of the input audio-frequency signal are distributed in the intermediate range of the audio-signal frequency band.

Abstract: The present invention concerns circuitry for comparing the output power of an amplitude modulated RF transmitter with the supply power to the RF transmitter and using feedback from a comparator to a variable gain modulation amplifier to maintain the level of modulation constant. The scheme is illustrated for four different basic types of RF amplitude modulated transmitters.