|Optical RX in small screened box attached to a 110mm drain pipe "stopper"|
Build method is my usual copper clad board with MeSquare pads built dead bug style. The junction of the SFH213 cathode and the gate of the FET must be kept well above the ground though to reduce losses.
To test the set up I modulate a small red LED mounted on the ceiling of my building shack with a 1kHz tone. With all lights out and in near total darkness I compare the level on the audio generator that I can just hear with that of my reference optical receiver. Both the new unit and the test unit are on the bench about 1.5m away from the (just glowing) LED. If the system is working well the S/N is good with the LED barely visible by eye. There are quantitative ways of measuring the sensitivity using Spectran on a PC but this means having the PC out of the room as the display would otherwise desense the RX!
I have yet to test this when mounted in the 110mm drain pipe with 100mm lens. This gives an antenna gain of around 24-30dB. A good test will be the GB3CAM optical beacon which I can just detect with my older head at a distance of around 32km.