Excerpts From Having Fun With ThroughtheAir Optical Communications

(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 N 6 IZW kbanke@sbcglobal. net

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)

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 1 mm square Fresnel lens ok but glass is better (heavier) 4” glass magnifier X 7850 gain ? ? d. B 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 K 3 PGP 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 He. Ne Lasers Chopped Using FAN for MCW Can be 10% AM Modulated Bragg Cell AM Modulator Laser Diodes - GHz bandwidth possible Typically 1 -2 milli. Radian (. 057 -. 114 deg) Spot Size > 100 Feet at 13 Miles Pulse On/Off Linear AM

35 KHz audio optical communicator schematic

Ramsey LBC 6 K 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). 3 W LED set new record of 173 miles 3 W LED cost is $8 LED (with optics) - 1. 4 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 128 -132 Hz Squaring circuit Divide by 2 64 -66 Hz Phase detector 64 -66 Hz 128 -132 Hz modulated light 120 VAC 128 -132 Hz Elgar variable frequency AC power source 150 W HPS Lamp VCO 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, KD 0 IFs IR laser transmitter with optical receiver

KD 0 IF equipment on Miguel facing Mt Soledad daylight operation

Tone with scintillation bouncing off retroreflector about 4 miles distance

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

Radio Mobile plot of terrain for 21 km NLOS path tested from N 6 IZW to W 6 OYJ

3 mile NLOS signal Displayed using Spectrum Lab Free softeware

Miguel optical beacon/repeater and microwave beacons

Bar Lens Preamp AGC Amp 196 LEDS 45 w 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 JT 441 PSK 31

Where to Find More Information http: //www. ham-radio/sbms/sd http: //www. qsl. net/wb 9 ajz/laser. htm http: //repairfaq. ece. drexel. edu/sam/lasercon. htm http: //www. k 3 pgp. org/ http: //pageperso. aol. fr/Yves. F 1 AVY/UKINDEX. html SDMG Contacts Kerry Banke N 6 IZW kbanke@sbcglobal. net Greg Bailey K 6 QPV gbailey@mail. sdsu. edu Ed Munn W 6 OYJ remunn@earthlink. net