having fun with through-the-air optical communications kerry banke n6izw kbanke@qualcomm.com updated...

Having Fun With Through-the-Air Optical Communications

Kerry Banke N6IZWkbanke@qualcomm.com

Updated 06/08/05

Basics of Common Amateur Equipment

Audio communicators

Wideband Laser Pointer link

Non- line-of-sight communication

Field Day Laser QSO

Modulated Light Sources

HeNe Lasers - Chopped Using FAN for MCWCan be 10% AM ModulatedBragg Cell AM Modulator

Laser Diodes & LEDs -Pulse On/Off Linear AMRed and I/R Wavelengths

Class 2A Visible Lasers (400 to 700 nm)

Lasers emitting visible light not intended for viewing, and under normal operating conditions would not produce a

injury to the eye if viewed directly for less than 1000 seconds.(i.e. bar code scanners)

Class 3a

Lasers that normally would not cause injury to the eye if viewed momentarily but would present a hazard if

viewed using collecting optics (fibre optics loupe or telescope).

Transmit Beamwidth

Laser - Typically 1-2 milliRadian (.057-.114 deg)Spot Size > 100 Feet at 13 Miles

LED (with optics) - 1.4 degreesSpot Size >1000 feet at 13 Miles

Photo Detectors

Photo Transistors -Sensitive but slow & Noisey

PIN Diodes - Fast But Lower Output Low Noise

LEDs - High efficiency LEDS look similar to Pin Diode in SensitivityRelative Speed & Noise Unknown

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800 HzOscillator

LEDor Laser

555Timer

Photo Detector

AudioAmp

Speaker

TelegraphKey

Photo Detector

AudioAmp

Speaker

LEDor Laser

AudioAmp

Microphone

Bias

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Basic 800 Hz MCW Link

Basic AM Voice Link

35 KHzVCO

PowerFET LED

Fresnel LensMicrophone

Audio Amplifier

Laser Pointer

PIN DiodePhoto Detector

35 KHz Amplifier

Mixer

145 MHzOscillator

Transmitted Red Light

Received Red Light

2M FMReceiver

145.035

Optical Communicator Block Diagram

W9FQN

35 KHz audio optical communicator schematic

TVCamera

CH3 RF Modulator

Video RF

LaserPointerAmp

0 dB

Mirror

Pin Photodiode

-45VDCBias

RF Amp

Television on Ch 3

MIC.

Basic TV Video/Audio modulated RF Laser pointer link - N6IZW - 05-16-05

Reasonably flat frequency response to 500 MHz and Useable to 1300 MHz

NLOS Communication Paths

Cloud Bounce

Dust/pollution/moisturescatter

TxLaptopwith PSK31

LaserDriverInterface

260 HzAudio 910 nm

LaserDiode & Lens

IR Tx Beam

IR RX BeamRx LensPin diodePreamp

RxLaptopwith PSK31

260 HzAudio

NLOS communicator setup using PSK31

4” opticsBoth Tx & Rx

Maximum distanced tested so far is 15 miles

3 mile NLOS signalDisplayed using Spectrum LabFree softeware

NLOS Reception equipment

Basic K3PGP type optical receiver used for NLOSExperiments. So sensitive you can hear the light from stars scintillating which sounds like wind rushing over a microphone

Simple Photo darlington photo detector for use with the soundcard in in a PC.

Laser

LED Tx

Rx

Rifle scope

Positioner

Front View

LED Tx unit

Laser

Rx unit

Scope

35 KHz audio communicator

LED Transmitter Early LED Tx unit capableOf 4 miles with 35 KHz communicator

Pin photodiode with preamp

35 KHz audio communicator

Fresnel Lens cut from plastic reading Sheet lens

Micrometer Az/El adjustmentMoves scope & Laser only

Where to Find More Information

A Construction Article for the 35 KHz optical communicator Publishedin June-Aug Issues of 73 Magazine byChuck WB6IGP Who is a Member of The San Diego Microwave Group and Writesthe “Above & Beyond” Column for 73 Mag.

Good Laser Web Site and Laser Email Reflector:http://www.qsl.net/wb9ajz/laser/laser.htm

LED/Reflector Test Fixture

Round reflector with LED in centerwhich is modulated at 35 KHZ.Used to align Tx & Rx optics

One end of 15 mile Field Day laser contact

Laser pointer seen from 15 miles away

Sun Relflected off mirror from Palomar Mt.