This was posted on the UKnanowaves Yahoo Group:
Greetings you light headed fellows :).Darker times are coming and the sun is going down earlier and earlier here in Finland.I've been designing an IR based repeater/beacon. When not in repeater use, it transmits FSK441 and CW. It has 6 of 850nm RX heads 0, 60, 120, 240, and 300 degree directions. This enables some selectivity by choosing best RX head by SNR from the received signals. It scans through all of the RX:s and if it detects an signal, it will switch to the best SNR (this is done by MCU).The TX is basically 10 IR leds transmitting simultaneously in all directions (they are spread over circular 360 degree form with 36 degree increments).I have 6 credit card size fresnel lenses that I was thought using in front of the six BPW34. I thought that a little off-focuse would make the system less prone about the direction of the signals. What worries me is the sun. This system will be installed relatively high and it is certain that the sun will be focused to the photodiodes time to time.Using a small IR filter in front of the BPW34 probably isn't the the best idea, because all of the energy from the sun is already focused to a relatively small area. Probably the best idea is to use the same sized IR filter than the primary antenna - the fresnel is. I've heard that exposed colour film would do a good job in this? Any experience?
Why I put two subjects under one message is that I just wanted to let you know what I'm doing, hi. And all the ideas will be taken in!
73 de Janne OH1SDR
PS. This repeater will have THz input and 70cm output and vice versa.