| 摘要 |
PURPOSE:To forcibly increase a variable speed of channel selection voltage, and also not to take a time for channel selection, by utilizing a frequency discriminating circuit for tuning to an AM broadcasting station, when the band is switched an FM band and is in a detuning state. CONSTITUTION:In case when the band is switched to an FM band by a band changeover switch 16, and the channel selection state is in a deturning state, voltage of 4.75V[=(3.5+6.0)/2]corresponding to a high speed search is supplied to a window comparator 24 by DC voltage E from a ratio detecting circuit 33 for receiving AM broad-casting. Accordingly, even if a noise level is small and also its DC component is varied, a high speed search can be executed irrespective of said factors. As a result, it does not take a time for channel selection. Furthermore, it is unnecessary to control the gain of an FM intermediate frequency amplifier 14F, etc. accordingly, and all inconveniences such as complicacy, etc. are removed. |
