In navigation transmitters it is important that the phase difference between the carrier waves of a carrier signal and the carrier waves of sideband signals be held at a constant value. To accomplish this, the carrier waves are maintained constant relative to a reference signal in a known manner. A phase meter measures the phase difference between the carrier waves of the sideband signals and the reference signal and between the carrier waves of the carrier signal and the reference signal. The measure values are used to determine the phase difference between the carrier signal and sideband signals which are compared with a desired value. Depending on the deviation from the desired value, a controllable phase shifter controls the phase of the carrier waves of the sideband signals. Since the measurements are made on a time-division multiplex basis, little circuitry is required. Any measuring errors do not affect the formation of the desired phase difference.

A device for pulse modulation automatic control, where the modulation is a combined plurality of pulse components. Each pulse component is singly controlled by a respective control voltage or current, the control voltages and/or currents being fully independent from the output demodulated pulse level and from the number, per time unit, of pulses.

The present invention relates to an improved goniometer circuit having extremely low modulation harmonic distortion characteristics, which is particularly suitable for use in a VOR navigation system. In the disclosed circuit, modulation harmonic distortion is greatly reduced by the use of a phase lock loop operating at small signal levels prior to the power amplification stage of the system. The phase lock loop employs a voltage controlled oscillator to completely eliminate harmonic distortion so that the final output of the system is virtually modulation free.