laser modulator laser beam concentrator (photos) laser beam concentrator (schematic) laser shotgun music on a light beam
These photos show some DX testing with the cheap laser modulator, receiver/demodulator, and associated (cheap) optical equipment (click the links above). Tests were made at 80' (24m), 500' (150m), 1200' (365m), 1 mile (1600m), 6.5 miles (10.5km) and 22 miles (35km). The tests were generally successful to the 6.5 mile test distance, though at 6.5 miles the sound was less than broadcast quality (future hardware enhancements may improve that). The photos are grouped by distance. Reference Test at 1 Foot (30cm)The cheap laser pointer is on the tripod, the photo-detector is in the foreground.The transmitted audio is a 1 kHz tone from a function generator. Test at 80 Feet (24m):Here's the transmit end of the beam.The laser pointer is installed in the mount at the left end of this rig. Receive end.For this test the receiver was co-located with the transmitter. 500 Feet (150m):Here's the transmit end of the beam.As you can see, it was dark outside (about 11 PM) though there was a nearly full moon. The receive end.The concentrator (see laser beam concentrator) is pointed, Another view of the concentrator. The laser beam as it shines in through the open door. A view of the laser beam through the concentrator. 1200 Feet (365m):The transmit end.In broad daylight this time. One Mile (1600m):The Transmit end.The transmitter is set up in a cemetery. An Entrepid Experimenter guards the transmitter during the test. Here's the receive end.This was the receiving location for both the 1200' and 1-mile tests. 6.5 Miles (10.5km):The transmitting end.The laser shotgun is in a barn. The receiving end.The received audio quality is mainly a function of the continuity of the laser beam. The biggest variable in this test seemed to be the ability of the operator/listener to keep the concentrator fixed on the beam. The sound was also probably affected by variations in air temperature ('heat waves' could be seen) and maybe the laser transmitter wobbling in the breeze (though the transmitter was protected in a barn). Higher quality optics and more stable mounts might greatly improve results. 22 Miles (35km):Transmit end.Receive end.A Big Gun is shown here, gunning for a laser beam. Here's a view through the concentrator.The laser pointer, 22 miles away, is the little red spot just to the left of the concentrator on the horizon. The camera imperfectly captures the effect. A 25-watt flashing strobe light co-located with the transmitting laser was totally invisible to the intreped observers. Only an occasional faint whisper of music could be heard through blasts of noise. The concentrator and sunset.A place called Pine Ridge, 22 miles distant from the transmitting laser. The receiving system seems to work as well (or poorly) in daylight as in darkness. |
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