Laser Communications

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

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

Human Spectral Response

Perceived Intensities WavelengthMultiplierColor 532 nm 28Green 635 nm 7Red-Orange 640 nm 5Red-Orange 650 nm 3Red 660 nm 2Red 670 nm 1Red

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

Pointer Design

Pointer Innards

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

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

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

Mounting Systems Mounts and stands need only be as accurate as beam divergence Mounts and stands need only be as accurate as beam divergence Good laser diodes will be 1-2mR (milliRadian) 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 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) 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. 1mR is 1.5' of divergence every 1000', 3' at 2000 ', etc.

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

Weak Signal Modes

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

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