Laser Communications

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).

Human Spectral Response

Perceived Intensities Red1670 nm Red2660 nm Red3650 nm Red-Orange5640 nm Red-Orange7635 nm Green28532 nm ColorMultiplierWavelength

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

Pointer Design

Pointer Innards

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 power o Minimum divergence Receiver o Maximum lens area o Clarity o Tight focus on detector

Filters Sun shade over detector Shade in front of lens Detector spectral response Colored filters o Absorb ~50% of available light o 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 June 08 - WA7LYI and KY7B miles ! Equipment used: 18 inch fresnel lens into Photomultiplier tube Transmitter: 15 mw helium cadmium laser (442 nm)

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