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Laser Communications

Laser Communications. Laser Classes. Class I – Sealed systems Class II – Output <1mW Class IIIa – Output 1mW - 5mW Class IIIb – Output 5mW – 500mW Harmful to eyes, diffuse viewing OK Class IV – Output >500mW Harmful to skin and eyes, diffuse viewing hazardous. Diode Lasers.

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Laser Communications

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  1. Laser Communications

  2. Laser Classes • Class I – Sealed systems • Class II – Output <1mW • Class IIIa – Output 1mW - 5mW • Class IIIb – Output 5mW – 500mW • Harmful to eyes, diffuse viewing OK • Class IV – Output >500mW • Harmful to skin and eyes, diffuse viewing hazardous

  3. Diode Lasers • Laser diodes emit an elliptical beam with astigmatism • Better units will include corrective lenses for astigmatism and to make the dot appear round • Neither of these problems are inherently bad for DX purposes but correcting them also improves divergence, a big win (more gain).

  4. Human Spectral Response

  5. Perceived Intensities

  6. Laser Diode Laser Diodes include Photodiodes for feedback to insure consistent output

  7. Pointer Design

  8. Pointer Innards

  9. Modulation • AM • Easy with gas lasers, hard with diodes • PWM (Pulse Width Modulation) • Used by Ramsey in their kit • PFM (Pulsed FM) • Potentially the highest bandwidth (>100kHz)

  10. Gain Systems • Transmitter • Maximum output power • Minimum divergence • Receiver • Maximum lens area • Clarity • Tight focus on detector

  11. Filters • Sun shade over detector • Shade in front of lens • Detector spectral response • Colored filters • Absorb ~50% of available light • Difficult to find exact frequency

  12. Mounting Systems • Mounts and stands need only be as accurate as beam divergence • Good laser diodes will be 1-2mR (milliRadian) • A 32 pitch screw at the end of a 2' mount will yield 1mR per revolution. Since quarter turns (even eighth turns) are possible, this is more than accurate enough • Higher thread pitches allow shorter mounts which may be more stable (against wind, vibration, wires) • 1mR is 1.5' of divergence every 1000', 3' at 2000 ', etc.

  13. Pointing • GPS and Compass • Scopes and Binoculars • Strobe lights, large handheld floods, headlights • HTs to yell when laser light is seen at remote location

  14. Weak Signal Modes

  15. Laser DX • 1991 - June 08 - WA7LYI and KY7B - 153.97 miles ! • Equipment used: 18 inch fresnel lens into Photomultiplier tube • Transmitter: 15 mw helium cadmium laser (442 nm)

  16. Applications • Transmit voice for miles line-of-sight • Use weak signal modes for “cloud scatter” • Transmit video with cheap pens • Transmit high speed data without WEP • Blind flies for easy extermination

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