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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 kbanke_at_sbcgloba
l.net
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Palomar Amateur Radio Club Microwave Net Meets
Mondays at 900 on Palomar 146.73- repeater San
Diego Microwave Group meets the third Monday of
each month at my home in La Mesa at
700 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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Fresnel Lens cut from plastic reading Sheet lens
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Simple Photo darlington photo detector for use
with the soundcard in in a PC.
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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 gt 100 Feet at 13 Miles Pulse
On/Off Linear AM
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35 KHz audio optical communicator schematic
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Ramsey LBC6K Laser Beam Audio Communicator Kit
Cost is about 37
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Reasonably flat frequency response to 500 MHz and
Useable to 1300 MHz
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One end of 15 mile Field Day laser contact
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Laser pointer seen from 15 miles away
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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 gt1000 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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Lee, KD0IFs IR laser transmitter with optical
receiver
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KD0IF equipment on Miguel facing Mt
Soledad daylight operation
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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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Radio Mobile plot of terrain for 21km NLOS path
tested from N6IZW to W6OYJ
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3 mile NLOS signal Displayed using Spectrum
Lab Free softeware
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Miguel optical beacon/repeater and microwave
beacons
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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-rad
io/sbms/sd http//www.qsl.net/wb9ajz/laser/laser.h
tm http//repairfaq.ece.drexel.edu/sam/lasercon.ht
m http//www.k3pgp.org/ http//pageperso.aol.fr/Yv
esF1AVY/UKINDEX.html SDMG Contacts Kerry Banke
N6IZW kbanke_at_sbcglobal.net Greg Bailey K6QPV
gbailey_at_mail.sdsu.edu Ed Munn W6OYJ
remunn_at_earthlink.net
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