ANTENNA TUNING CIRCUIT FOR CAR AM AND FM RADIO RECEIVER

摘要

PURPOSE:To obtain a tuning frequency superior in rejection of interference wave removal characteristics, by providing antenna tuning circuits which use varactor diodes for AM and FM very closely to an antenna and obtaining the tuning frequency having sufficient tracking with a reception side. CONSTITUTION:The tuning circuits 4 and 5 which use the varactor diodes 10 and 13 for AM and FM are provided very closely to the antenna 1. Consequently, antenna serial capacity in the AM band and parallel capacity by a coaxial feeder are obtained and the influence of the latter is nearly eliminated to perform tuning while the entire AM band is covered within the variable capacity range of a varactor diode put on the market. On the other hand, transmission loss exerting influence upon the SN ratio of a low-level signal is reduced even in the FM band.