A narrow band complex input signal, typically having multiple independently modulated carriers, is processed to produce an output signal. The process separates the multiple input signals (10) into an amplitude-limited angle-modulated carrier component (14) and an envelope component (18), and then combines these components by a form of pulse-duty-factor modulation such as pulse-duration modulation (16), at a sufficiently high sampling rate. The combined signal is input to a nonlinear power amplifier (22). Unwanted sidebands are rejected by bandpass filtering (24) at the amplifier output so as to pass only the carrier and its signal bandwidth.

Transmission of multiple carrier signals in a nonlinear system

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.

Method and apparatus for controlling the carrier of an amplitude-modulated transmitter

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.

Pulse width modulator for AM-RF transmitter

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. Thereby, the power amplifier is forward biased but not driven into saturation during the short duration pulses. The switch provides a higher impedance path from the timing circuit to the reference potential terminal after the transition has elapsed, enabling the power amplifier to be saturated during pulses longer than the short duration pulses. The RF power amplifier tube has a tendency to load the power amplifier tube out of saturation during wide pulses. The ampitude of the wide pulses is maintained substantially constant by a resistor shunted by an inductor between the modulator and the power amplifier.

RF-AM transmitter with pulse width modulator

In a wired remote control for use with a television receiver, audio signals are coupled to a loudspeaker by a transformer providing electrical isolation. The remote control device comprises an oscillator applying a signal at a frequency above the audio range to the transformer and a rectifier at the transformer secondary converting the oscillator signal to a DC signal. That DC signal is selectively applied by a switch to an optocoupler which couples to a control device for controlling the audio source. A filter blocks the oscillator signal from the speaker. Additionally, the control device controls TV channel selection.

Wired remote control apparatus for a television receiver

The transmitter has a carrier control and includes an exciter for supplying the carrier voltage to a modulation stage, usually the final RF-power amplifier of a broadcast transmitter, with the modulation voltage having a controlled dc content. The modulation voltage is amplified in a modulation amplifier and the amplified modulation voltage is supplied to the modulation stage. The modulation amplifier includes a switching amplifier producing pulse duration modulated pulses, a modulation voltage controlled pulse duration modulator preceding the switching amplifier and a filter section following the switching amplifier. An adder element is connected in advance of the modulation amplifier, specifically in advance of the modulation voltage-controlled pulse duration modulator. The applied modulation voltage is supplied to a rectifier followed by a filter section and the filter section is connected to a control element and supplies thereto a variable direct voltage as a volume-dependent control magnitude which contains also very low frequency components in accordance with the volume of the modulation voltage. The output of the control element is supplied to the adder element for combining with the modulation voltages supplied to the modulation amplifier to change the pulse duty factor of the output pulses of the switching amplifier as required for carrier control of the transmitter. The volume control magnitude supplied from the control element can be additionally superposed by a fixed direct voltage to establish the average pulse length of the output pulses of the pulse duration modulator and thus to establish the average direct voltage value of the filter section of the modulation amplifier and the average operating point of the modulation stage.

Bodo Wysocki

Papers

Amplitude modulated transmitter