| 摘要 |
PURPOSE:To prevent the variation of frequency characteristics of the stages of amplification of intermidiate frequency in both cases of UHF and VHF reception by attaching capacity elements for UHF tuning in parallel with switch diode for alteration. CONSTITUTION:Capacitor 14 is set in parallel in alteration switch diode D5 which alters between UHF and VHF. Since D5 is connected in case of VHF reception, capacitor 14 shorts at the portion of D5 and shows the status like a equivalent circuit (A); since D5 is shut off in case of UHF reception, capacitor 14 is arranged in series with 11 and the equivalent circuit shows (B). Where, Cv and Cu are respectively the output capacity of transistor 1 at the time of VHF and UHF reception. It is necessary to equlize the turning capacity of both VHF and UHF reception for giving the same characteristics of frequency to both of VHF and UHF reception, so that capacity C14 of capacitor 14 should be found so that formula (4) is satisfied. It is very easy to find C14 form formula (4). |
