G8AGN's FREE-SPACE LED COMMUNICATIONS PAGE



Here are some pictures of my gear and details of tests

updated 25 August 2013

 

G8AGN My first optical contact using a LED Tx was with Gordon, G0EWN/P, on 7 Oct 2010.
The path length was 10 km, with G0EWN/P at Skew Hill and G8AGN/P at Roper Hill, both sites being on the west side of Sheffield.
The Tx was based on a LuxeonIII high power LED, modulated with either a 1 KHz tone or speech using a VK7MJ linear modulator. The Tx is the square box on the right of the picture. The sighting scope has x 4 magnification.
The cylinder on the left of the picture is the old G0MRF Rx which was last used in my laser tests in 2004.

 
VK7MJ This is the VK7MJ modulator. Note the power transistor bolted to the side of the die-cast box and the high wattage resistor which limits the maximum current flowing through the LuxeonIII LED.

 
LuxeonIII This shows the LuxeonIII mounting arrangements and the focussing slide.
The LuxeonIII needs an adequate heat sink since it dissipates at least 3 watts. To ensure proper illumination of the A4 size Fresnel lens, a special FRAEN narrow beam secondary lens is placed immediately in front of the Luxeon LED.
The focussing slide is moved relative to the Fresnel lens using a threaded rod arrangement.

 
LuxeonIII This shows a top view of the the LuxeonIII mounting arrangements and the focussing slide.

 
G8AGN/P's This shows G8AGN/P's LuxeonIII Tx at Roper Hill as seen by G0EWN/P at Skew Hill.
The Luxeon is the faint red dot in the middle of the picture. It is not very bright, probably because of misalignment. Note the light pollution caused by floodlights on a nearby sports field!

 
G8AGN/P's This shows G8AGN/P's LuxeonIII Tx at Roper Hill as seen by G3PHO/P at Skew Hill during a one-way test on 20 Oct 2010.

 
G8AGN/P This shows G8AGN/P's equipment set up on 6 Nov 2010 at Edgemount, on the NW side of Sheffield, for a test with G0EWN/P at Emley Moor, a path distance of 20 km.
As well as the LuxeonIII Tx and the old G0MRF Rx, a new combined Tx-Rx was by then under construction. This is shown in the background. The new Rx is based on the KA7OEI v3 design and this test was used to set up the optimum focus point for the photo-diode. The new Rx proved to be very much more sensitive than the G0MRF design.

 
G0EWN/P This shows G0EWN/P's LuxeonIII Tx at Emley Moor as seen by G8AGN/P at Edgemount.
Look for the red dot which is just to the left of the vertical row of red lights on the TV tower.

 
G8AGN/P This shows G8AGN/P's LuxeonIII Tx at Edgemount as seen by G0EWN/P at Emley Moor.
Look for the red dot in the centre of the picture.

 
G8AGN This shows a front view of G8AGN's latest combined Tx and Rx. The Fresnel lenses are A4 page magnifiers.
The receiver front-end is based on KA7OEI's v3 circuit and the LuxeonIII is modulated with either tone or speech using a linear "precision current-sink" circuit developed also by KA7OEI.

 
G8AGN This shows a back view of the combined Tx and Rx. The die-cast box on the left contains the receiver back-end. There is space inside the box for future additional features such as an audible S meter and DSP filtering.
The die-cast box on the right contains the linear modulator.

 
KA7OEI This shows the KA7OEI linear modulator for the LuxeonIII LED.
The LED current is varied using a power FET. The white rectangle on the left side of the picture is a 1 ohm current sensing resistor.

 
Inside This shows a view of the LuxeonIII and the KA7OEI receiver front-end, each of which is mounted on an individual focussing slide with facilities for lateral adjustment. The latter ensure that the Tx and Rx beams can be collimated with the spotting scope

 
G8AGN This shows G8AGN's combined Tx and Rx assembled on its tripod and ready for a QSO with G0EWN/P over a 66km path. This two-way contact was made on 24 Nov 2010.
G0EWN/P was at Roper Hill, on the west side of Sheffield. G8AGN/P was near Harpswell, east of Gainsborough.
The small black box on top of the rig is a PIC callsign generator which is used to key the 1 kHz tone during initial alignment.

Listen to G8AGN/P's signal as received by G0EWN/P (1MB)

Listen to G0EWN/P's signal as received by G8AGN/P (1MB)

Listen to G0EWN/P's signal after QRM due to street lights has been removed using SpectrumLab (1MB)

 
G8AGN/P This shows G8AGN/P's equipment set up on 8 Sept 2012 at Totley Moor, on the SW side of Sheffield, for a test with G0EWN/P on the North Yorkshire Moors, a path distance of 129.1 km and a new UK record.
The equipment, mounted on a modified golf trolley was a combined Tx/Rx with interchangeable Tx and Rx heads and a single A4 size Fresnel lens. The Rx is based on the KA7OEI v3 design and the Tx is based on a Luminus CBT40 Phlatlight high power LED.

 
G8AGN/P This shows G8AGN/P's equipment set up on 16 Aug 2013 at High Bradfield, on the NW side of Sheffield, for a test with G0RPH/P on the Lincolnshire Wolds, a path distance of 83.4 km and a new UK DAYLIGHT record.
The equipment, uses separate Tx and Rx each with its own A4 size Fresnel lens. The Rx is based on the KA7OEI v3 design and the Tx is based on a Luminus CBT40 Phlatlight high power LED.

 

 


Links Suppliers, other laser info and projects, safety


Contact Barry, G8AGN mailto:B.Chambers@shef.ac.uk