[Laser] LEDs as photodiodes

[Stuart]

Steve,


Since I discovered that LEDs would work as photo diodes, I used a few 5mm high brightness types before I discovered that the high power Golden Dragon LEDs make good stable detectors when reverse biassed to 43V. I have since checked that in my receive circuits they have a response measured with my SDR set-up about 1dB down on the SFH2030 photo diode used before. For my LOS sub-carrier FM and SSB this loss is more than compensated for by the convenience of having the thing work on both RX and TX. There are several sets built to the same spec that work equally well in this area. The LED is Osram LR W5SM-HYJY-1. Others will probably work also. This trick works at 850nm and 940nm also, without the need for such high bias (Osram make these in the Golden Dragon series also). Since you are in "UKNanowaves" you can look at my Radcom series of articles in the files area to see how to get rid of the protective anti-parallel diode.


Stuart