1. Laser Communications

2. 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

3. 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).

4. Human Spectral Response

5. Perceived Intensities
Wavelength
Multiplier
Color
532 nm 28
Green
635 nm 7
Red-Orange
640 nm 5
650 nm 3
Red
660 nm 2
670 nm 1

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

7. Pointer Design

8. Pointer Innards

9. Modulation AM PWM (Pulse Width Modulation) PFM (Pulsed FM)
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)

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

11. 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

12. 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.

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

14. Weak Signal Modes

15. 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)

16. 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