19 Feb 2010
Before I became a radio ham, a friend and I had our first phone wireless QSO using a small torch bulb modulated with a couple of germanium transistors. The DX was across the road, about 20m at most. At the far end the receiver was based on an OC71 with its black coating scraped off, which made quite an effective photo transistor. These days there are much better ways. For some examples, see some of the fascinating links at http://www.carolinaflashers.org/ . One of these days I must revisit optical communications. The picture on the right is from http://www.laud.no/ww2/lispr/index.htm and shows a WW2 lightbeam communications device used by the German Army.