| 摘要 |
PURPOSE:To enable inexpensive mutual simultaneous calling without fail by linking an antenna conductor with an opened acoustic waveguide tube to the sound collection hole of a receiver microphone through an insulating distance tube at a base part of a box body installation. CONSTITUTION:With the uniform acoustic waveguide tube diameter by a tube antenna electric conductor 20, the acoustic transmission loss is small and the built-in microphone 21 can collect sounds located in the opening edge of the antenna conductor 20. In short, the sound collection sensitivity of the microphone 21 for caller voice is high, and the sound collection sensitivity for a distant receiver speaker 11 is low. Thus, echo and howling generation can be suppressed as well as transmission sound collection S/N can be improved. The antenna gain and radiation efficiency of radio waves from antenna can be improved by the radial counterpoise conductive of leg parts 9a to 9c. |
