STEPS INTO THE LIGHT!
article that follows describe some basic attempts at light wave communication
by G3PHO and G8AGN. We had both experimented with HeNE gas lasers
some years ago but had not tried much in the way of point-to-point
communications. This time, using laser diode techniques and low voltages
(rather than the 2kV used on the gas lasers of yesteryear!), we had
immediate success over a short 0.6km path. Read on...
Here's a photo of me, G3PHO,
trying to burn a hole in my hand! Seriously, it demonstrates the
laser transmitter used in a recent test with Barry, G8AGN.
On the 2nd of July 2004,
Barry and I carried out a simple TX/RX test across the Redmires
Reservoir in Sheffield. Barry had made both items of equipment and
was anxious to see if they would work over a short path. I operated
the transmitter unit which was mounted on a very small tripod and
placed on an aluminium step ladder, which in turn stood on a stone
wall! We didn't need a more sturdy mount in view of the short distance
the right you can see the laser as seen by the receiver at the other
end of the path. It's a very intense red light, even in the comparatively
bright evening conditions. The receiver was mounted on camera tripod,
adequate for this test but certainly not steady enough for the long
distance paths we have planned for future tests.
These lightwave tests remind
me of my early days on microwaves, back in the 1970s, when equipment
was light weight and low power(a few milliwatts). The sheer simplicity
of early 10GHz wideband equipment encouraged me to climb mountains
with it to increase distances worked. I can see myself doing this
again but with the lightwave gear this time!
As with microwave contacts,
a liason (talkback) frequency is used on another band. For the lightwave
tests we used low power, licence free, 70cm (446MHz) handhelds.
These are very cheap to buy in the UK (less than £20 for two
units!) and have a useful range of a few kilometres. Naturally we
will revert to the more usual 144MHz ssb for longer paths we hope
to try in future.
photo on the right shows the lightwave receiver constructed by G8AGN.
It has an OPT210 photo diode and AF amplifier, set up behind a 100mm
glass lens (a hand magnifier from Maplin Electronics). Barry found
that B&Q (and other DIY stores presumably) sell a nice piece of
black plastic tubing, made by Marley and used for ventilation ducting
through brick walls. The tube is about 250mm long and the lens is
a reasonably snug fit inside. At present, the tube is stuck on Barry's
camera tripod with duct tape!
the Transmitter,shown to the left, Barry uses a laser pointer driven
by a square wave via an
emitter follower. This produces an unmistakeable tone in the receiver.
In fact I could clearly hear it coming from Barry's receiver across
the lake, a distance of 0.6km! Note the telescopic sighting tube mounted
on top of the laser housing. This has a cross hair sight to enable
accurate pointing of the equipment.
Further tests are planned
and we hope to exchange reports via speech modulation instead of
We have a long way to go
to reach the high standards already established by our more experienced
lightwave friends G8LSD, G0MRF, G0FDZ and G3GRO but it's going to
be a lot of fun along the way!
You can read about other
UK lightwave work elsewhere on this website and at others: