Method and arragnement for digital transmission using AM emitters

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.

Description

technical field

[0001] The present invention relates to the field of broadcast transmitters which are converted from analog amplitude modulation (AM) to digital modulation as digitization advances. Background technique

[0002] In this context, the invention is to enable the continued use of the type of transmitter commonly used today, a non-linear AM transmitter featuring an RF input (radio frequency) as well as an audio input. The reasons are as follows:

[0003] AM transmitters work internally in switch mode and thus have 3 times better efficiency than linear transmitters, which are usually used for digital transmissions, eg for DAB (Digital Audio Broadcasting) and DVB (Digital Video Broadcasting). This results in savings in operating costs.

[0004] Convincing broadcasters that the switch from analog to digital is more convenient if there is no major initial investment.

[0005] Digitization of AM broadcasting can be seen as the only chance to maintain these frequency...

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