[Laser] led transceiver

[stuart.wisher at talktalk.net]

Tim,



You said my 6.5km contact using the led transceiver was a record, I was using a 12dB attenuator in line with the lens at the time (1" dia hole in cardboard in front of 4" lens which attenuates both receive and transmit) which means the system is capable of at least 26km. Actually we set out to test this last week but the rain came down before I could switch over from the Fresnels. All this with zero bias on the led. 


I tested this rig using reverse bias in the lab and the gain comes up another 12dB at 33V bias, after that it makes a good noise generator. All this gives the rig a potential range of 100km.


I have measured some of the frequency response of several heads, The VK7MJ design, K3PGP, and KA7OEI all run up to 100kHz using capacitor coupling and a reverse biassed SFH2030 diode (only 11pF on spec sheet). Clint's may go further but I didn;t check since we usually use about 25kHz FM and LSB.


I am constructing Mk2 LED transceiver at the moment using a power led that works as a photo diode, with bias circuit and separate power supply (batteries)built in. The current drawn is only 0.1 micro amp so the batteries will last for their shelf life.


Stuart G8CYW