A high frequency SSB radio transmitter has an envelope amplitude modulator for varying the envelope of an rf signal source based on an error signal from envelope detectors detecting the envelope of the input and output waveform It also has a first phase modulator in a main feedback loop for varying the phase of the input waveform based on differences detected in a phase detector between the instantaneous phase of the input and output rf signal To overcome the problem of spurious outputs from the phase detector resulting from the cross-over points of the SSB waveform when there are carrier breaks and other problems, a subsidiary, phase lock loop feeds a signal derived from the error signal to a second phase modulator to tend to hold the inputs to the phase detector in such a phase relationship that the output is zero To cope with large phase shift errors between the input waveform and the output which result when the power amplifier changes frequency or temperature variations eg at the antenna, a broadband phase shifting network is brought into operation when a dual voltage comparator senses that the signal fed to the second modulator passes a value corresponding to its extremes of adjustment

Circuit for reducing distortion produced by an r.f. power amplifier

An RF pulse transmitter, for use in precision distance measuring equipment (DME/P) of a microwave landing system, includes appropriate circuitry to correct for incidental phase modulation (IPM). The pulse transmitter includes a modulation circuit for generating an RF pulse having a pulse peak. A reference phase control circuit is provided to generate a reference signal. A phase detector receives the RF pulse and the reference signal and in response thereto generates a phase error signal. The reference phase control circuit includes appropriate circuitry for adjusting the phase of the reference signal applied to the phase detector to thereby drive the phase error signal to a predetermined value at the pulse peak. A pre-distortion circuit generates a pre-modeled correction signal pulse for use in correcting for incidental phase modulation (IPM). A phase correction control circuit receives the phase error signal and in response thereto modulates the phase of the carrier signal to correct for the incidental phase modulation.

RF pulse transmitter having incidental phase modulation (IPM) correction

A double-sideband amplitude modulated (DSBAM) carrier passed through band-pass circuits wich are too narrow for the modulated carrier or are misaligned, may have one or both side-bands altered in relative amplitude, or in phase relative to the carrier. These effects result in amplitude modulation distortion and produce angle modulation of the carrier, with the same waveform as the amplitude distortion. In this invention the angle modulation is detected and applied to an amplitude modulator in the required phase and amplitude to substantially eliminate the distortion of the modulated carrier.

Modulation distortion reducer

The invention relates to an apparatus for precise modulation of signal phase and signal delay, respectively, and signal amplitude, comprising a first fixed-delay device having its input coupled to an input signal, a first variable delay device having its input coupled to said input signal and having a control input for delay adjustment, a first amplitude control device in series with the first variable delay device, providing at its output an amplitude controlled signal and having a control input for adjusting the output amplitude, a phase detector with linear characteristic having its two inputs connected to the output of the fixed-delay device and the output of the first amplitude control device, an error measurement device having its negative input connected to the output of the phase detector and its positive input connected to a control signal, an amplifier with low-pass characteristic having its input connected to the output of the error measurement device and its output to the control input of the first variable delay device.

Phase and amplitude modulator

A digitally modulated RF amplifier system is presented having improved adjacent sideband distortion reduction. This system includes the provision of a first RF carrier signal at a first frequency within a first frequency channel having adjacent channels. A modulator receives a digital information signal and modulates the first RF carrier signal with the digital information signal to provide a digitally modulated RF signal within the first RF channel. A second RF carrier signal is provided having a second frequency spaced from the first frequency channel by a frequency that is greater than the bandwidth of the first channel. The digitally modulated RF signal is combined with the second RF carrier signal to provide a combined RF signal which is then amplified resulting in an amplified RF signal having reduced adjacent sideband distortion products. The amplified RF signal is then applied to a bandpass output filter for removing the second carrier signal and other signals that are of frequencies which are outside of the first channel and its adjacent channels.

Digitally modulated RF amplifier system having improved adjacent sideband distortion reduction

Means, including a voltage controlled oscillator in a phaselocked loop, whereby the transmitted carrier frequency is locked to a source of carrier frequency generation. The loop loop includes AM modulator AM modulator such that coincidental phase modulation is removed from AM transmitted AM modulated carrier.

H Stover

Papers

Means to prevent coincidental phase modulation in an amplitude modulation transmitter