| 摘要 |
<p>A portable transmitter intended to be used to broadcast a signal in response to an external actuation can be constructed so as to include a board such as a so-called printed circuit board carrying a metal coil serving as an antenna. This coil surrounds a central region of the board carrying the operative components of the transmitter other than the antenna and carrying as much excess metal as can be conveniently located generally within the antenna. With this structure, the components and any metal located as described serve as capacitance adjacent to the antenna. As a consequence of the structure the effect of any capacitance adjacent to the exterior of the transmitter is minimized so as to improve antenna performance. When the antenna forms a part of an oscillator circuit in the transmitter so as to determine the oscillator frequency this structure minimizes the effect of any capacitance external to the transmitter affecting the oscillator frequency.</p> |
