LASER Communication

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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
 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).
Human Spectral Response
 Perceived Intensities
 Laser Diode
 Pointer Design
 Pointer Innards
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)
Gain Systems
 Transmitter
 Maximum output power
 Minimum divergence
 Receiver
 Maximum lens area
 Clarity
 Tight focus on
detector
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
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.
Pointing
 GPS and Compass
 Scopes and Binoculars
 Strobe lights, large handheld floods, headlights
 HTs to yell when laser light is seen at remote location
Weak Signal Modes
Laser DX
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