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(Excerpts From) Having Fun With Through-the-Air Optical Communications Presented to: Palomar Amateur Radio Club 02-06-08 The San Diego Microwave group Kerry Banke N6IZW [email protected] Palomar Amateur Radio Club Microwave Net Meets Mondays at 9:00 on Palomar 146.73- repeater

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(Excerpts From)

Having Fun With

Through-the-Air Optical Communications

Presented to:

Palomar Amateur Radio Club

02-06-08

The San Diego Microwave group

Kerry Banke N6IZW

[email protected]


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Palomar Amateur Radio Club Microwave Net

Meets Mondays at 9:00 on

Palomar 146.73- repeater

San Diego Microwave Group meets

the third Monday of each month at

my home in La Mesa at 7:00

Covering from 1000 MHz through light

(also an occasional Beta or Gamma ray)


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Overview

The light spectrum

Optical receivers & sounds

Modulated light sources

Line-of-sight communications

Non-LOS communications

SDMG Optical Repeater/Beacon


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Photo Detectors

Photo Transistors - Low MHz bandwidth

Sensitive but slow & Noisy

PIN Diodes - Fast But Lower Output

Low Noise - GHz bandwidth possible

LEDs - High efficiency LEDS look similar

to Pin Diode in Sensitivity

Relative Speed & Noise Unknown


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Lenses

Act like antenna - Larger aperture means

higher gain with more directivity

Typical gain increase is about the ratio of

lens diameter to the photodetector area

Small photodiodes about 1mm square

Fresnel lens ok but glass is better (heavier)

4” glass magnifier X7850 gain ??dB

Available for less than $2

Narrow band optical filters allow

daytime operation




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Basic K3PGP type optical receiver used for NLOS

Experiments. So sensitive you can hear the light from

stars scintillating which sounds like wind rushing

over a microphone


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Modulated Light Sources

HeNe Lasers -

Chopped Using FAN for MCW

Can be 10% AM Modulated

Bragg Cell AM Modulator

Laser Diodes - GHz bandwidth possible

Typically 1-2 milliRadian (.057-.114 deg)

Spot Size > 100 Feet at 13 Miles

Pulse On/Off

Linear AM







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LEDs

Major improvements in the last few years

Standard high intensity 20 ma LED good

for several miles(audio bandwidth).

3W LED set new record of 173 miles

3W LED cost is $8

LED (with optics) - 1.4 degrees

Spot Size >1000 feet at 13 Miles

20 MHz bandwidth possible


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Lamps

Incandescent - Low depth of modulation

Fluorescent,Mercury & Sodium Vapor

Good depth of modulation

Work well with frequency modulation

using Jason Software


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HPS lamp modulation scheme

128-132 Hz

Laptop

with Jason

SW

Squaring

circuit

Divide

by 2

64-66Hz

Phase

detector

64-66 Hz

128-132 Hz

modulated

light

120VAC

128-132 Hz

Elgar variable

frequency AC

power source

VCO

Error

Voltage

150W

HPS Lamp


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Making an optical contact

Pointing requires good Az/El control

LEDs much easier due to wide beam

Aligned rifle scope or viewing through

receiver optics

Target must be visible unless precise Az/El

calibration and data is available

Liason radio link for coordination

and audio pointing feedback

Scintillation is a real issue




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Tone with scintillation bouncing off

retroreflector about 4 miles distance


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Cloud Bounce

Bounce off objects

Dust/pollution/moisture

scatter

NLOS Communication Paths



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3 mile NLOS signal

Displayed using

Spectrum Lab

Free softeware



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196

LEDS

196

LEDS

45w

45w

Power

Amp

Bar

Lens

AGC

Amp

Preamp

Miguel linear optical repeater


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LED/Reflector Test Fixture

Round reflector with LED in center

which is modulated at 35 KHZ.

Used to align Tx & Rx optics


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Free software we use for our

optical communications experiments

Spectrum Lab

Spectran

Jason

JT441

PSK31


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Where to Find More Information

http://www.ham-radio/sbms/sd

http://www.qsl.net/wb9ajz/laser/laser.htm

http://repairfaq.ece.drexel.edu/sam/lasercon.htm

http://www.k3pgp.org/

http://pageperso.aol.fr/YvesF1AVY/UKINDEX.html

SDMG Contacts

Kerry Banke N6IZW [email protected]

Greg Bailey K6QPV [email protected]

Ed Munn W6OYJ [email protected]


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