1. Through-the-Air Optical Communications
Having Fun With
Through-the-Air Optical Communications
Kerry Banke N6IZW
Updated 06/08/05

2. Basics of Common Amateur Equipment
Audio communicators
Wideband Laser Pointer link
Non- line-of-sight communication
Field Day Laser QSO

4. 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

5. 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).

6. Transmit Beamwidth
Laser - Typically 1-2 milliRadian ( deg)
Spot Size > 100 Feet at 13 Miles
LED (with optics) degrees
Spot Size >1000 feet at 13 Miles

7. 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

10. W9FQN

11. 35 KHz audio optical communicator schematic

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

14. Cloud Bounce
Dust/pollution/moisture
scatter
NLOS Communication Paths

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

16. 3 mile NLOS signal
Displayed using
Spectrum Lab
Free softeware

17. NLOS Reception equipment

18. 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

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

20. Laser

21. Rifle scope
Positioner
LED Tx Rx

22. 35 KHz audio communicator
Front View
Scope
Laser
Rx unit
LED Tx unit

23. LED Transmitter Early LED Tx unit capable Of 4 miles with 35 KHz
communicator

24. Pin photodiode with preamp
35 KHz audio
communicator

25. Fresnel Lens cut from plastic reading
Sheet lens

26. Micrometer Az/El adjustment
Moves scope & Laser only

27. 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 Reflector:

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

29. One end of 15 mile Field Day laser contact

30. Laser pointer seen from 15 miles away

31. Sun Relflected off mirror from Palomar Mt.