Radio-frequency receiving circuit

摘要

A radio-frequency receiving circuit is proposed, the IF filter of which is controlled in dependence on the direct-current component and the alternating-current component of the demodulated IF voltage (UNF) in such a manner that the instantaneous intermediate frequency is always within the passband of the IF filter (12) and the IF filter is tuned to the respective carrier of the intermediate frequency. For the circuit to work correctly even after dips in the received field strength, the circuit contains in a channel (25) carrying the direct-current component an electronic memory circuit (32) which stores the last direct-voltage value present in the case of a voltage dip and forwards this value to the control input (41) of the IF filter. When voltage dips last longer, a change-over switch (34) located between the memory circuit and the control input (41) of the IF filter ensures that the direct-current value of the memory circuit is replaced by a direct-current value corresponding to a centre position of the IF filter within the IF passband. <IMAGE>