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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
[email protected]
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 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 (.057-.114 deg)
Spot Size > 100 Feet at 13 Miles
Pulse On/Off
Linear AM
Microphone
Audio
Amplifier
Fresnel Lens
35 KHz
VCO
Power
FET
LED
Transmitted Red Light
Laser
Pointer
145 MHz
Oscillator
35 KHz
Amplifier
PIN Diode
Photo Detector
2M FM
Receiver
145.035
Mixer
Optical Communicator Block Diagram
Received Red Light
35 KHz audio optical communicator schematic
Ramsey LBC6K Laser Beam Audio Communicator Kit
Cost is about $37
TV
Camera
CH3
RF Modulator
Laser
Pointer
Amp
0 dB
Video
RF
Mirror
MIC.
RF
Amp
Pin Photodiode
Television
on Ch 3
-45VDC
Bias
Reasonably flat frequency response to 500 MHz and
Useable to 1300 MHz
Basic TV Video/Audio modulated RF
Laser pointer link
- N6IZW - 05-16-05
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) - 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
64-66Hz
Phase
detector
64-66 Hz
128-132 Hz
modulated
light
120VAC
128-132 Hz Elgar variable
frequency AC
power source
150W
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, 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
Cloud Bounce
Bounce off objects
Dust/pollution/moisture
scatter
NLOS Communication Paths
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
Bar
Lens
Preamp
AGC
Amp
196
LEDS
196
LEDS
45w
45w
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
http://www.ham-radio/sbms/sd
http://www.qsl.net/wb9ajz/laser/laser.htm
http://repairfaq.ece.drexel.edu/sam/lasercon.htm
http://www.k3pgp.org/
http://pageperso.aol.fr/YvesF1AVY/UKINDEX.html
SDMG Contacts
Kerry Banke N6IZW [email protected]
Greg Bailey K6QPV [email protected]
Ed Munn W6OYJ [email protected]