Abstract: A method for avoiding spurious emissions in an AM transmitter for digital transmission includes converting a digital modulation for controlling the AM transmitter into an amplitude signal for an amplitude branch, and a phase-modulated RF signal for a RF branch. Non-linear distortions in an amplitude response and a delay-time characteristic of an amplitude branch are compensated for using a pre-equalization with inverse shapes by measuring and storing the amplitude response and the delay-time characteristic of the RF branch. An inverse transfer function is determined using respective shapes of the measured amplitude response and delay-time characteristic by an inverse Fourier transform. An equalizing network is dimensioned for the determined inverse transfer function. The equalizing network is connected in series upstream of the RF branch. The amplitude and RF branches are combined downstream of the amplitude and RF branches.

Abstract: A method for digital transmission using an AM transmitter includes operating an output stage of the AM transmitter in a linear mode and correcting the supply voltage of the output stage in the linear mode as a function of an instantaneous drive so as to improve efficiency. The correcting is performed by operating the modulator of the AM transmitter as a switched-mode power supply unit so as to deliver a corrected supply voltage to the output stage, and scanning an envelope of a complex modulated data signal so as to control the correcting. A time constant during the scanning of the envelope enables immediate following of a rise in the envelope. The complex modulated data signal is delayed after the scanning so as to perform the correcting during the delay and prevent an overdriving of the output stage.

Abstract: A method for avoiding spurious emissions in an AM transmitter for digital transmission includes converting a digital modulation for controlling the AM transmitter into an amplitude signal for an amplitude branch, and a phase-modulated RF signal for a RF branch. Non-linear distortions in an amplitude response and a delay-time characteristic of an amplitude branch are compensated for using a pre-equalization with inverse shapes by measuring and storing the amplitude response and the delay-time characteristic of the RF branch. An inverse transfer function is determined using respective shapes of the measured amplitude response and delay-time characteristic by an inverse Fourier transform. An equalizing network is dimensioned for the determined inverse transfer function. The equalizing network is connected in series upstream of the RF branch. The amplitude and RF branches are combined downstream of the amplitude and RF branches.

Abstract: A method for avoiding spurious emissions in an AM transmitter for digital transmission includes converting a digital modulation for controlling the AM transmitter into an amplitude signal and a phase-modulated RF signal. Non-linear distortions in an amplitude response and a delay-time characteristic of an amplitude branch are compensated for using a pre-equalization with inverse shapes by: measuring and storing the amplitude response and the delay-time characteristic of an amplitude branch; determining an inverse transfer function using respective shapes of the measured amplitude response and delay-time characteristic by an inverse Fourier transform; dimensioning an equalizing network for the determined inverse transfer function; and connecting the equalizing network in series upstream of the amplitude branch. An equalizing network is dimensioned for the determined inverse transfer function. The equalizing network is connected in series upstream of the RF branch.

Abstract: A method for reducing out-of-band emission in an AM transmitter for digital transmission includes generating, from a digital modulation signal, an amplitude signal and a phase-modulated radio frequency signal configured to control the AM transmitter. A digital modulation process is used in which a hole is formed around a 0/0 point so that a zero crossing is avoided by a substantial margin in a vector diagram representation. Thereby a respective bandwidth of the amplitude signal and the phase-modulated radio frequency signal is limited so that the out-of-band emission decreases as a function of a shoulder distance achievable by the AM transmitter at a rate where a spectrum mask is not exceeded.

Abstract: A method for reducing out-of-band and spurious emissions of AM transmitters in digital operation includes providing an amplitude signal and an RF-P signal from a digital modulation signal. The RF-P signal is tapped in the RF branch and the tapped signal is passed through a Gaussian filter in a separate branch, the Gaussian filter having a linear phase. The filtered RF-P signal is fed to an envelope detector to detect amplitude variations. The detected amplitude variations are combined as a correction signal with the amplitude signal in a multiplier in the A branch to produce a corrected amplitude signal. The corrected amplitude signal is fed to the linear input of the transmitter output stage and multiplied by the RF-P signal.

Abstract: Digital transmission using existing AM transmitters leads to the problem of the occurrence of unwanted out-of-band and spurious emissions. The reasons for this are that the two signals A-signal and RF-P signal, which are generated from the digital modulation signal (I/Q signal) and which are required for controlling the AM transmitter, have considerably larger bandwidths than are available in the separate branches A branch and RF branch and that the two signals arrive at the multiplier of the transmitter output stage with a delay. Using the known methods for delay compensation to below 0.3 microseconds and bandwidth reduction, for example, by a hole in the vector diagram of the I/Q signal around the 0/0 point, it is not possible to minimize the out-of-band and spurious emissions to a sufficient degree.

Abstract: In digital transmission using AM transmitters, non-linear distortions occur because of the band limitation in the amplitude branch and also in the RF-branch, resulting in unwanted spurious emissions. In order to meet the requirements of the ITU, it is required to achieve constant shapes of the amplitude response, the phase response and the delay-time characteristic in the amplitude branch and also in the RF-branch and to compensate for the propagation time difference between the two branches. In the RF-branch, the required bandwidth can be achieved by suitable selection of the quality of the resonant circuits. For the amplitude branch, a pre-equalization with an inverse transfer function is applied to compensate for the non-linearities. To apply the method, it is required for the amplitude response and the delay-time characteristic to be determined with measuring techniques and to be stored. The transfer function for the equalizing network is determined by an inverse Fourier transform to the measured values.

Abstract: During digital transmission using existing non-linear AM emitters, spurious emissions occur as a result of the non-linear distortions, in turn causing inner band disturbances and also disturbing adjacent channels, as out-of-band radiation. Non-linear distortions are especially critical for digital multiple carrier signals (e.g., OFDM) which are recommended by the ITU with the DRM system for the AM area. In order to avoid the non-linear distortions, the end step of the AM emitter is operated in the linear mode, thus ensuring the ITU spectrum mask. The relatively low efficiency of the emitter during the linear operation can be improved by tracking the distribution voltage of the emitter end step according to the drive. To this end, the envelope of the complex modulated data signal is scanned, and said signal controls the distribution voltage for the emitter end step by means of the modulator operating as a switched-mode power supply unit.

Abstract: The problem associated with digital transmission using existing AM transmitters is that the out-of-band emission that occurs must be reduced in order to comply with the ITU mask, as the shoulder distances that can be achieved by the AM transmitters are not sufficient for a satisfactory compensation. The signals that are required to control the AM transmitters, (amplitude signal and phase-modulated RF signal), are formed from the digital modulation signal by a Cartesian polar transformation, whereby the bandwidth for the amplitude signal and RF signal reaches a value, which causes an unacceptable out-of-band emission. To prevent this, the invention provides methods for digital modulation, which avoid the zero point by a wide margin in their vector diagram representations, i.e. which form a “hole” around the 0/0 point. Modulation methods of this type are referred to as offset modulations and coded modulations.

Abstract: A method for the transmission of digital signals, particularly in the AM bands (broadcasting bands), with high-level modulation, preferably 32 APSK or 64 ASPK, being used for data blocks to be transmitted. At the receiving end, time-periodic measurements of a noise are carried out and noise signals determined therefrom are subtracted from received signals.

Abstract: Through a memory device and a control circuit on the transmitter side, temporal gaps are inserted into the data stream, said temporal gaps being removed again on the receiving side by an additional memory device. Consequently, the necessary continuous data stream is able to be reproduced for the transmission of the video signals. The gaps in the data stream of the base station and the data and the requests are evaluated by a user-side control circuit, from these, switch-over signals are generated, and the user devices are switched over. The base state switches the station to receive mode in the temporal gaps of the video signals or of the data stream. The present invention is applicable to the transmission of continuous signals using a backward channel via microwaves.