| 摘要 |
<p>An AM/EM/CB antenna (11) includes a frequency trap (16) at a position above the lower end of the antenna such that the electrical length of the lower section (14) of the antenna is equivalent to one-quarter wavelength for a frequency in the FM frequency band. The trap (16) presents a high impedance in the FM frequency band and prevents the flow of FM frequency signals from the upper antenna section to the lower section. The entire length of the antenna (11) is equivalent to one-quarter wavelength in a frequency in the CB frequency band. The antenna wire (12) is wound around a fiberglass core (13), and the FM trap (16) is formed by a tightly wound, coiled section of the wire together with a thin-walled brass tube extending over the core (13) in the area of the tightly wound section. A thin dielectric film is applied between the tube and the tightly wound section of antenna wire thereby forming a capacitor.</p> |
