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Abstract

Frequency diversity is employed to counter selective fadings as a result of multi-path propagation for troposcatter and short-wave connections for digital useful signals employing frequency modulation. For this purpose, the digital useful signal is supported on a frequency arrangement comprising at least three radio frequencies in that the digital useful signal, together with at least one additional oscillation, and, in fact, an additional fundamental oscillation which determines the frequency of the spacing in radio-frequency frequency arrangement, is fed to the input of a frequency modulator. At the input end, the radio-frequency carriers of the frequency arrangement, which are each modulated with the useful signal, are all converted by coherent mixing into the same frequency level, from which, by way of a combiner, a sum signal is obtained which is the optimum in respect of signal-to-noise ratio.

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First Claim