Here are some pictures of my gear and details of tests

updated 9 January 2011

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.

 

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.

 

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.

 

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

 

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!

 

This shows G8AGN/P's LuxeonIII Tx at Roper Hill in QSO with G0EWN/P at Skew Hill on 14 Oct 2010.

 

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.

 

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.

 

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

 

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.

 

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.

 

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.

 

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.

 

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

 

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)

 

This shows a KA7OEI audible S meter. During initial link alignment, the transmitter broadcasts an AM modulated 1 KHz tone. The resulting 1KHz signal from the receiver generates another tone whose pitch varies wth the amplitude of the received signal. Then to align a receiver one simply adjusts the azimuth and elevation for maximum S meter pitch. To align the transmitter, the S meter tone is relayed back via a talk-back link and the transmitter direction adjusted for maximum S meter pitch.

 

When receiving signals over a path which crosses urban areas, QRM due to street lights may be a problem. This board contains a KA7OEI PIC comb filter which filters out harmonics of either 50 or 60Hz. The code offers a choice of four filtering algorithms.

 

A tight squeeze! This is the latest G8AGN optical receiver back-end. The left-hand board contains the audible S meter. The right-hand board contains the PIC comb filter for hum removal. The audio amplifier is on the small board in the bottom left-hand corner of the box. On the box lid are a function switch and two pots. One of these controls the S meter/filter gain and the other is for the audio gain.

 

This shows G8AGN's optical Tx-Rx set up near Pocklington on the Yorkshire Wolds on 8 January 2011. The aim was to work G0EWN/P, at Roper Hill near Sheffield. This is a path length of 87 km.

 

G8AGN/P's Luxeon as seen by G0EWN/P at Roper Hill. Look for the faint red dot in the centre of the picture.

 

G0EWN/P operating at Roper Hill during the record breaking contact. The back covers on Gordon's rig have been removed temporarily to allow fine adjustments to be made to the optics. Reports for the two-way voice contact were only 5-2 but the sky was not fully dark at that time. Eventually the contact was terminated because of impending hyperthermia but as the sky darkened, signal levels were still noticeably rising. Listen to G0EWN/P's signal as received by G8AGN/P (1MB)

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