Laser Communications
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Laser Classes
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Class I – Sealed systems
Class II – Output <1mW
Class IIIa – Output 1mW - 5mW
Class IIIb – Output 5mW – 500mW
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Harmful to eyes, diffuse viewing OK
Class IV – Output >500mW
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Harmful to skin and eyes, diffuse viewing hazardous
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Diode Lasers
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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).
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Human Spectral Response
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Perceived Intensities
Wavelength
Multiplier
Color
532 nm
28
Green
635 nm
7
Red-Orange
640 nm
5
Red-Orange
650 nm
3
Red
660 nm
2
Red
670 nm
1
Red
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Laser Diode
Laser Diodes include
Photodiodes for
feedback to insure
consistent output
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Pointer Design
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Pointer Innards
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Modulation
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AM
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PWM (Pulse Width Modulation)
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Easy with gas lasers, hard with diodes
Used by Ramsey in their kit
PFM (Pulsed FM)
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Potentially the highest bandwidth (>100kHz)
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Gain Systems
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Transmitter
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Maximum output power
Minimum divergence
Receiver
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Maximum lens area
Clarity
Tight focus on
detector
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Filters
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Sun shade over detector
Shade in front of lens
Detector spectral response
Colored filters
Absorb ~50% of available light
 Difficult to find exact frequency
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Mounting Systems
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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.
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Pointing
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GPS and Compass
Scopes and Binoculars
Strobe lights, large handheld floods, headlights
HTs to yell when laser light is seen at remote
location
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Weak Signal Modes
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Laser DX
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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)
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Applications
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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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