| 摘要 |
<p>A tuner for receiving a broadcasting signal whose frequency band is divided into high and low channels is disclosed. In this case, the tuner has first and second filters whose pass bands are fixed, a switch changeably connected to one of output terminals of said first and second filters, said switch being so changed that upon receiving a low channel said switch is changed to one state to deliver only a signal belonging to the low channel in said broadcasting signal from said first filter while upon receiving a high channel said switch is changed to the other state to deliver only a signal belonging to the high channel in said broadcasting signal from said second filter, a local oscillator, a mixer which is supplied with a local oscillation signal from said local oscillator and a signal from one of said first and second filters to be multiplied with each other, and means for deriving a signal from said mixer which belongs to a predetermined band as an intermediate frequency signal, and if it is assumed that the lowest and highest frequencies in the lowest band of said low channels of said broadcasting signal are taken as f1L and f1H, respectively; the lowest and highest frequencies of the highest band of the low channels of said broadcasting signal as f3L and f3H, respectively; the lowest and highest frequencies in the lowest band of said high channel of said broadcasting signal as f4L and f4H, respectively, the lowest and highest frequencies in the channel occupying the highest band of said high channel of said broadcasting signal as f12L and f12H, respectively; the band width of one channel of said broadcasting signal as fB; and the lowest frequency of the intermediate frequency signal as fL, respectively, and an upper heterodyne system is employed, the following conditions are satisfied; ....... (1) ....... (2) or ........ (3) and or ........ (4) while under the same assumption but a lower heterodyne system is employed, the following conditions are satisfied; , , ..... (5) or ..... (6) and or ..... (7)</p> |
