本文的研究目的為探討自由空間中利用光傳輸NTSC影像訊號的特性。係利用發光二極體為發射端，而光電接收二極體做為接收端，經由空氣從發射端傳送至接收端，來傳輸NTSC影像訊號。 本系統採用振幅調變的方式來作訊號的調變，並經由濾波器來有效隔絕一般低頻背景光的環境干擾。然而，發射光源選取可見光二極體的優點，在易於實驗時用肉眼判斷傳輸是否中斷等狀況，於實際運用時可用紅外光取代，並可藉由增加發射功率，以延長通訊距離。 因此選定自由空間中光傳輸作為研究之方向，探討自由空間中光的傳輸行為，及利用電性的方式控制信號輸出行為，我們並利用自動增益放大器，使信號落於後級電路可以接受的電性範圍之內，而擴大了信號接收的範圍，目前本論文可將通訊距離延長至約一公尺。 In this study, we considered the communication characteristics ofan NTSC imaging signal in free space by light transmission. Toaccomplish this purpose we used an LED and a photodiode as thetransmitter and the receiver, respectively. The amplitude of the signal was modulated in our system and thelow frequency background noise isolated by an electrical filter. Thechoice of a visible-light LED as our light source made it easy to checkif signal transmission had stopped, however this could be replaced byan infrared LED, in which case we could extend the communicationdistance by enhancing the power of the LED. In addition, we also used an auto-gain amplifier to adjust thesignal of the post-circuit, to keep it within an acceptable range. Thisalso expanded the range of the received signal. In our experiments thecommunication distance was about 1 meter.
