Figure 1 The Laser receive system Note 1: The 10 pF capacitor removes the low frequency component (AC) from the optoaetector A: o'-? 2 The 12pF capacitor on the first stage of the TL-064 prevents osaftaions and improves stab ly 'Jote 3: Adjust the teedbac* neh\'Ork on the fast stage of the TL-064 to maximize ar your frequency iapprox 1 kHz) Response is broadband in nature
Stanford CA &4309 A complete lOmV* laser head and 12 voii power supply from Karl cost only $ 100. and 2 to 3 mW lasers are quite a bit less. He also stocks laser related components, including laser pointers in the 2 lo 3 mW range (small) and higher power pointers. I purchased a system from him and was very pleased. He also has 2 to 4 mW pointers, all operating from 12 volts DC.
In our first experiment, we used a laser transmitting over a Two mile plus path with the beam so bright al the receive site that it appeared lo be four city blocks on fire. There was not a city light, even at a nearby shopping center complex with all the sodium parking tights on, that could give a comparable brightness on the horizon. Only the street light nearby was comparable, but it wasn t as bright as the iaser At this iwo-mife distance, the 1 milliradian spot size (at the transmitter) had increased to a 5-fool wide spot
Let's gel into ihe details of the sys-lem that Kerry W61ZW and I pui together for the lesi just described, The taser power supply was operaied from ihe 110 VAC mains, so it remained at Kerry s home Modulation of the laser was done with a 12 volt DC muffin fan The receiver was a photo PIN detector salvaged: from scrap mecical equipment The detector was tied to a currens amplifier for a firsi stage to give low noise amplification of the signal coming from the selector Tne rema ningcircuitry ¡s an audio amplifier that amplifies the 1000 Hz modulation from the transmitter.
Many different types ot lenses employed on a hand held optical bench to evaluate the performance of the test tens anc the detector It *as found that a Radio Shack "cigarette" parabolic reflector about three inches
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