Tuning device for round radio receiver with an automatic search sweep

摘要

1342809 Signal seeking receivers; AFC systems AUTOVOX SpA 21 March 1972 [31 March 1971] 13087/72 Headings H3Q and H3A In a tuner control device for the automatic and manual control of a tuner where the tuner 2 is controlled by a memory unit 9 and a bi-stable circuit 6, by the output of a discriminator 3 during automatic signal search so as to stop the search in the vicinity of a received signal, the outputs of the discriminator 3 and of a manual tuning circuit 12 are connected to a control circuit 5 for tuning and the memory unit 9 is connected with a discharge circuit 8 and a charging circuit 7 which have inputs connected to the output of the control circuit 5. A further input of the discharge circuit 8 is connected with the output of a return circuit 11 and a further input of the charge circuit 7 is connected with the output of the bi-stable circuit 6 and the arrangement is such that the automatic signal search ceases in the vicinity of the frequency of the signal on the change of state of the bi-stable circuit 6 and the charging circuit 7 is actuated by the control circuit 5 until tuning is achieved. The return circuit 11 enables the tuner to restart the scanning from one end of a band when it has reached the other end of the band. An amplifier 4 is connected between the discriminator 3 and the control circuit and the bi-stable circuit 6 and 13 provides automatic tuning control. When the bi-stable circuit 6 is switched in the scanning position the charging circuit 7 conducts and charges the memory unit capacitor 9. The output across the capacitor 9 is fed via a buffer 10 to vary the resonance frequency of the tuner circuits 2 by electrical means, such as variable capacity diodes. When a signal is detected the output from the discriminator 3 changes the state of the bi-stable circuit 6 which stops the charging circuit 7. Tuning is completed using the output from the amplifier 4 which information permits the control circuit 5 to actuate the charging circuit 7. When the correct tuning is obtained the output from the discriminator 3 blocks the charging circuit 7. A transistor circuit for the amplifier 4 and the circuits 5, 6, 7, 8, 10 and 11 is disclosed (Fig. 2, not shown). Manual adjustment of the tuning may be effected by moving the wiper of a potentiometer (24) from a central position to which it is spring biased. The circuit 14 operates to reduce the sensitivity of the tuner 2 or the medium frequency circuits and to silence the L.F. circuits during the automatic signal sweep.