| 摘要 |
PURPOSE:To make high speed the automatic channel selection and high S/N for the compatibility, so that the time constant of LPF connected to the phase comparator output can be selected or made variable. CONSTITUTION:When the frequency is changed with automatic channel selection, since muting is made to the radio audio output, S/N is not taken as any problem, and at normal reception, high speed response of PLL is not entirely taken as any problem since the frequency is not required to be changed and the time constant of LPF of PLL can be greatly changed depending on the relation before and after. That is, the LPF5 at the output side of the phase comparator 4 is greatly changed for the time constant with the signal line (a) from the controller 8. The controller 8 counts up the counter stored up to now with the instruction from the keyboard 9, the result is delivered to the programmable divider 3, and the audio sound of radio set is stopped by giving muting signal to the muting circuit 11 at the same time, signal (a) is delivered to LPF5 and the time constant can sufficiently be set shorter. |
