At 17.51 13/03/2004 -0500, you wrote: >Read all your questions. > >We currently have stations working each other over a 22 mile line of sight >path with LED transmitters. Very interesting. What bandwidth do you achieve? >Forget building a photodiode/op amp receiver. You can buy top of the line >Burr-Brown opt-301 ($16, comes in a shielded can package) or BurrBrown >opt-101's ( $6. same electronics, but unshielded DIP package). If you are >interested in the opt101 unit, it's being sold for $2.50 each at this >moment. These Burr Brown units are very very hot receivers and include the >op amp and photodiode in the same package. They draw 120 microamps from a 5 >volt supply, so there's alot of sensitivity available for low $$! I'll look into the datasheet, thanks. >For less than optimum sensitivity requirements, TAOS has a whole line of >optical receivers (photodiode/amp assy) in the same package-their prices >are $3 to $2.50 each. Taos sends free 'samples'. Nice. >Are you a member of the of the laser communications email list??? These >guys do many different modes and have good general knowledge of lightwave >transmitters and receivers. They are mostly ham radio operators, but there >is no licensing requirement on the lightwave bands, so the list is open to >all who have an interest in lightwave communication. > >For serious distance, use an 8 by 10 fresnel lens (commonly called a page >magnifier), available for 6 bucks at you local office supply or stationary >store. > >My interest is in extremely weak non line of sight troposcatter >communications (also known as over the horizon communications by the >military). For this, photomultiplier tubes, big light collectors and >optical passband filters are required and the rates are 1 to 3 bits per >hour using .001 Hz bandwidth receivers (DSP soundcard/PC with good >software). Others in the group do high speed digital modes, still others do >carrier modulated studio quality audio transmissions. I guess that such datarates aren't achieved by troposcatter systems, right? >If I can help further, send me a message off list. Thanks for the info.. your post was very helpful. Greets, Andrea >Art > >At 09:37 AM 3/13/04, you wrote: >>Hi all, >>I'd like to build myself a Long-Range, Low-Power IR Transceiver. >>I know that the "long range" and "low power" may seem contraddictory, >>but I thought, if I produce a very intense but very brief IR "flash", >>the flash may be visible at a long distance, yet the average power >>will be low. Rather than emitting 30mW for 5mS, I could emit 3000mW >>for 50uS, with the same average power, but the intensity would be 100 >>times higher (and the range, IIRC, 10 times longer). >>I intend to encode data by time-modulating these pulses, e.g. at a 1mS >>rate transmit both clock and data (one clock and one data bit/pulse, in >>sequence, continuosly.. clock pulse always present, data pulse present >>if "1" and absent if "0"). >>The receiver would filter out DC, through a high-pass filter to detect >>almost only those very brief pulses, and nothing else. >> >>Does my design makes sense? >> >>I'm now on the component identification phase. I examined the datasheets >>of all the IR LEDs and photodioes/phototransistors that my favourite >>online shop sells (small shop but excellent service and prices), and I >>selected these devices: >> >>tx: >>TSHA6203 (875nM) >>TSIP5201 (950nM) >> >>rx: >>BPW83 (875nM and 950nM) >> >>The other devices I examined in detail were: >>BPW21, BPW34, BPW40, BPW41, BPW42, BPW77N, TSTS7103 >> >>But I'd have some questions for you: >> >>1) All the rest being equal, what wavelength is preferable, 875nM or >> 950nM? I know that 875 would be better if there're glasses inbetween, >> but my application will be mostly free air. >>2) What is in general preferable on the receiver side: photodiode or >> phototransistor? Why? >>3) Do you have any better LED and photodiode/phototransistor to advice >> than the ones I selected? I'd have no problems to buy those from >> another shop.. if it's worth the extra shipping charge, etc.. of >> course (i.e. I'd have to make two orders instead of one). >>4) How does the world look like, at those wavelengths? Is it generally >> "dark", or at 875-950nM reflections and absorbtions from objects is >> more or less like visible light? >>5) At such high pulse currents, should I fear damage to my eyes if I >> accidentally look into the (invisible) beam? >>6) To increase further the range, I'm thinking about making a 2m long >> tube, internally reflective (aluminium foil), diameter slightly more >> than the IR LED. This should decrease the angle of emission, but also >> make it more powerful and concentrated, right? (i.e. a bit like a >> poors' wannabe laser). >> For the receiver I'm thinking about using a small telescope, pointing >> it to the transmitter (hopefully 1+ Km away.. ehm). Will the lens be >> transparent for the incoming 875nM or 950nM light? >> >>Thanks! >>Andrea >> >>-- >>http://www.piclist.com hint: The list server can filter out subtopics >>(like ads or off topics) for you. See http://www.piclist.com/#topics > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics