FREQUENCY TRANSPOSITION OF ANALOG SIGNALS FREQUENCY TRANSPOSITION OF ANALOG SIGNALS

In an arrangement for transposition of the frequency band of an analog signal the analog signal is first converted into a digital signal in an analog-to-digital converter. The digital output of the converter is connected to a multistage shift register operated with shift pulses having a pulse width less than half the pulse width of the highest frequency analog signal. A first weighting network is connected to each stage of the shift register and multiplies the information in the associated stage by a factor corresponding to a Fourier expansion of a desired transfer function resulting in a digital bandpass filter. The output of the weighting network is combined in a combination network and reconverted into analog form in a digital-to-analog converter. In order to correct for distortions due to the limited number of shift register stages at least one additional weighting network is connected to the shift register stages for providing a transfer function with the same bandwidth as the transfer function provided by the first weighting network, although the transfer function of the additional weighting network is shifted in phase with respect to that of the first weighting network. As with the first weighting network a digital-to-analog converter connected to a combining network for the additional weighting network provides analog signals. The analog signals associated with the first weighting network modulate the output signal of a carrier frequency generator, while the analog signals associated with the additional weighting network modulate a phase shifted version of the output of the carrier frequency generator. The phase shifted modulated carrier is then subtracted from the modulated carrier in an additional combining network thereby removing the objectionable portions of the modulated carrier produced by the distortions from the shift register and first first weighting network.