These pages form part of the European Microwave
News web pages, please feel free to browse around the rest of the site
after you have finished here! The EMN is a free service dedicated to microwave
radio above 1 GHz and to any mode, be it SSB, CW, ATV or Data.
Although at the highest end of the microwave spectrum,
these pages cover many aspects of lasers and the communications experiments
being made with them
What are 'Laser Communications'?
Simply, the use of lasers as the communications
medium, rather than using traditional radio links. Specialised transmitter
and receiver circuitry is required to modulate the laser beam and to recover
the modulation at the receiver. For many years, a number of US amateurs
have been using lasers for communications purposes and commerical laser
links are readily available. However, most of these experiments and commerical
links operate over a few hundred metres. In recent years these path lengths
have been extended and K3PGP has recently managed to hold a QSO over a
26 KM path using clodu scatter! With current technology and more importantly,
cost of laser diode modules, these path lengths could be extended. Indeed,
K3PGP is trying to complete the worlds first amateur moonbounce laser QSO!
Welcome to the amazing world of laser communciations!
What is a Laser?
Laser is an acronym for:
A laser usually consists of an active medium that
amplifies light, combined with mirrors and lenses that bounce the light
back and forward until it finally escapes from the laser as a beam.
Laser beams have a set of specific characteristics
Highly directional, parallel beam of light
Single, or narrow, portion of the spectrum
There are many different types of laser medium,
some of the more popular types are:
Solid State (Ruby or YAG)
Gas (Argon, Helium-Neon, CO2)
Semiconductor (Laser Diode)
How Do I Build A Laser Transceiver?
A complete transceiver in its basic form can be
seen below, The transmitter consists of a simple laser diode module, this
can be either a dedicated module or a unit from a laser pointer. This is
'modulated' by a small tone generator unit, which generates an 800 Hz square
wave. The laser beam is then cycled on and off by the 800 Hz square wave,
you can see this by sweeping it quickly across a wall and seeing the broken
The receiver is based around a phototransistor
amplified by a small opamp. The recovered audio is fed to a speaker and
audio amplifier. The receiver module receives the modulated beam and recovers
the 800 Hz modulation and amplifys this into an audio tone.
Jim GM4RJX's Laser
Some practical applications using
basic laser equipment!
A real life laser QSO!
The brightness of a laser, even over distance,
has got to be seen to be believed! This image taken by Jim using his digital
camera shows the laser of Mark GM4ISM being seen at night over a 50 KM
path. The skyline is that of Glasgow and Mark was located at the Blackhill
transmitter site (halfway between Glasgow/Edinburgh). The laser is a bright
dot on the horizon and having seen it over a similar path, the only way
I can describe it, is like a car brake light! It's that bright! And it
does really stand out from the general brightness of other objects at night.
Jim 'illuminated' first!, using the navwarn lights of the tower as aiming
point. Two metres was used a talkback. Once jim had aligned his laser,
Mark used his laser light as an aiming point, as Jim was on a darkened
hillside to the North of Glasgow. A two way QSO followed. The plan next
is to find a longer path that is line of sight and dark, preferably with
two visual aiming points! Certainly it would have been possible to extend
the path to twice the 50KM - the only problem is finding suitable, and
The transmitter side of the laser unit uses a
small, and very low power laser pointer module. These are removed from
standard laser pointers! They have an output of only 2-5 mW! A typical
unit is shown here. The laser is the small brass coloured block at the
right of the unit. It has a small collimating lens in front of it (for
focusing). The laser is normally supplied by by a simple battery supply,
but in our applications the switch and battery are bypassed and the voltage
feeding the laser is modulated at 800 Hz by a small switching supply. This
gives an 800 Hz tone in the receiver speaker.
In a darkened room, the persistence of human vision
allows you to see the on-off ratio of the 800 Hz pulses! The on-off switching
can be seen in the image above.
laser mounting is all important if you want to be able to point it in the
right direction and keep it there. Minute movements at one end of the link
will set the laser beam off by metres at the other end, over even short
links. Longer paths are impossible if the laser is not mounted well. Jim's
laser is built like the proverbial brick outhouse! It is mounted on large
steel conduit and uses two slow motion motors to aim the laser in both
vertical and horizontal azimuths. He also uses a motor controller circuit
to slow the motors down even more! Consequently his aiming is very easy
even over long paths. This picture also shows the additional gadgets fixed
to his tripod mounted equipment, this includes imaging equipment to see
over long paths (the visual version of a preamp!) and an infra-red, low
light camera to see IR wavelength lasers. Jim is planning some QRO experiments
with a 35 mW IR laser. Basic tests (in the shack) so far show that it is
capable of burning paper at close range!
More Updates Later!
If you would like more information on laser communications
or would like to arrange a sked please email Jim