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设计德克萨斯州唯一的RF通信链路
许多无线连接,例如电话和wi-fi,都是双向的,甚至可以是全双工的。然而,许多应用程序都存在,其中传输仅是给定设计和应用程序所需的全部。这通常会带来独特的限制。例如,你的汽车无钥匙进入系统需要体积小,功率低,并传输一个独特的键控信号,具有足够的发射功率在各种天气中都是可靠的。相应的基站通常不受空间限制或功率限制,并且只容纳设计的接收部分。
简单但不有效
单独地,rf发射级可以由单个晶体管电路完全处理(图1)。它甚至不使用微控制器。机械开关适用于功率振荡器晶体管Collpits,使用Hartley,或调谐电路。稳定的交流正弦波形辐射通过简单的天线。在接收端,调谐电路可以使用简单的二极管作为检测器,并恢复按下按钮的有效信号。这基本上是一个AM载波/载波只在无线传输链路上。
Figure 1: The simplest TX only AM Carrier On /Carrier Off RF transmitter can be built using a single transistor and some passive components.
While a useful demonstraTIon, this may not be an effecTIve design. Every TX/RCV pair would have to be tuned to a different frequency; otherwise you can only use one in any given area. Temperature and component drift would also make this a poor design from a reliability standpoint.
To be useful, a coded signal that can be easily assigned during manufacturing needs to be transmitted on a stable carrier. This maTIng code needs to be easily set at the receive board as well.