Laser Communications. Laser Classes Class I – Sealed systems Class II – Output
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Transcript of Laser Communications. Laser Classes Class I – Sealed systems Class II – Output
Laser Classes• Class I – Sealed systems• Class II – Output <1mW• Class IIIa – Output 1mW - 5mW• Class IIIb – Output 5mW – 500mW
o Harmful to eyes, diffuse viewing OK• Class IV – Output >500mW
o 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).
Perceived Intensities
Red1670 nm
Red2660 nm
Red3650 nm
Red-Orange5640 nm
Red-Orange7635 nm
Green28532 nm
ColorMultiplierWavelength
Modulation• AM
o Easy with gas lasers, hard with diodes• PWM (Pulse Width Modulation)
o Used by Ramsey in their kit• PFM (Pulsed FM)
o Potentially the highest bandwidth (>100kHz)
Gain Systems• Transmitter
o Maximum output powero Minimum divergence
• Receivero Maximum lens areao Clarityo Tight focus on
detector
Filters• Sun shade over detector• Shade in front of lens• Detector spectral response• Colored filters
o Absorb ~50% of available lighto 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
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)