(Excerpts From) Having Fun With Through-the-Air Optical Communications Presented to: Palomar Amateur Radio Club The San Diego Microwave group Kerry Banke N6IZW

Palomar Amateur Radio Club Microwave Net Meets Mondays at 9:00 on Palomar 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)

Overview The light spectrum Optical receivers & sounds Modulated light sources Line-of-sight communications Non-LOS communications SDMG Optical Repeater/Beacon

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

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

Fresnel Lens cut from plastic reading Sheet lens

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

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

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 ( deg) Spot Size > 100 Feet at 13 Miles Pulse On/Off Linear AM

35 KHz audio optical communicator schematic

Ramsey LBC6K Laser Beam Audio Communicator Kit Cost is about $37

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

One end of 15 mile Field Day laser contact

Laser pointer seen from 15 miles away

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) degrees Spot Size >1000 feet at 13 Miles 20 MHz bandwidth possible

Lamps Incandescent - Low depth of modulation Fluorescent,Mercury & Sodium Vapor Good depth of modulation Work well with frequency modulation using Jason Software

HPS lamp modulation scheme Laptop with Jason SW Squaring circuit Divide by 2 Phase detector Elgar variable frequency AC power source VCO Hz Hz 150W HPS Lamp 120VAC Hz modulated light Error Voltage

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

Lee, KD0IFs IR laser transmitter with optical receiver

KD0IF equipment on Miguel facing Mt Soledad daylight operation

Tone with scintillation bouncing off retroreflector about 4 miles distance

NLOS Communication Paths Cloud Bounce Dust/pollution/moisture scatter Bounce off objects

Radio Mobile plot of terrain for 21km NLOS path tested from N6IZW to W6OYJ

3 mile NLOS signal Displayed using Spectrum Lab Free softeware

Miguel optical beacon/repeater and microwave beacons

196 LEDS 196 LEDS 45w Bar Lens Preamp AGC Amp Power Amp Miguel linear optical repeater

LED/Reflector Test Fixture Round reflector with LED in center which is modulated at 35 KHZ. Used to align Tx & Rx optics

Free software we use for our optical communications experiments Spectrum Lab Spectran Jason JT441 PSK31

Where to Find More Information SDMG Contacts Kerry Banke N6IZW Greg Bailey K6QPV Ed Munn W6OYJ