| 摘要 |
PURPOSE:To perform continuous reception of 120-300MHz by using two varactor diodes connected in series and parallel to tuning coils of the input circuit, interstage circuit and oscillating circuit of a tuner which receives even the CATV band. CONSTITUTION:An input signal of VHFTV is inputted from a terminal (a), passed through an IF trapping circuit (c), and RF-amplified by a MOSFETQ1, and through cascaded transistor (TR)Q2 and Q3 for a mixer, an IF output converted by a TRQ4 for oscillation is outputted to a terminal (b). High-frequency tuning coils L1-L2 are each switched between a high and a low band through a switching diode SWD. To coils of an input, an interstage and an oscillating tuning circuit, varactor diodes CD1 and CD2 are connected in parallel and in series respectively, and then varied by an output from a power terminal Bt for tuning. This constitution provides continuous reception of the CATV band of 120-300MHz. |
