Through-the-Air Optical Communications Having Fun With Through-the-Air Optical Communications Kerry Banke N6IZW kbanke@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 MCW Can be 10% AM Modulated Bragg Cell AM Modulator Laser Diodes & LEDs - Pulse On/Off Linear AM Red 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 degrees Spot 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 Sensitivity Relative Speed & Noise Unknown

W9FQN

35 KHz audio optical communicator schematic

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

Cloud Bounce Dust/pollution/moisture scatter NLOS Communication Paths

4” optics Both Tx & Rx Maximum distanced tested so far is 15 miles

3 mile NLOS signal Displayed using Spectrum Lab Free softeware

NLOS Reception equipment

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

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

Laser

Rifle scope Positioner LED Tx Rx

35 KHz audio communicator Front View Scope Laser Rx unit LED Tx unit

LED Transmitter Early LED Tx unit capable Of 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 adjustment Moves scope & Laser only

Where to Find More Information A Construction Article for the 35 KHz optical communicator Published in June-Aug Issues of 73 Magazine by Chuck WB6IGP Who is a Member of The San Diego Microwave Group and Writes the “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 center which 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.