G0EHV – Light Communications

Under Construction

Light

I’ve only just got going on “Lightwaves” (Nov 2010) but already I’m hooked on this interesting medium.

There are a group of radio amateur operators in N.E. England who are keen and active. They are G8CYW (Stuart), G8KPD (Brian), G8PNN (Gordon), G4MSF (Keith), M0DTS (Rob) and myself who have working systems and have had QSO’s.

Other interested amateurs are G8POG, G4WAX, G4KUX, G1LPS, G4FVP and one or two others who are either building kit or have assisted at /P expeditions to the hill tops of N.E. England!

My Activity

My first QSO was with Rob M0DTS/P on 15/11/2010 at a distance of 37 Km. A recording can be seen/heard here.

Despite several trips out to test, there has been poor weather over the winter of 2010/11 with no real visibility to improve on my first QSO.

However I managed to get out and have a QSO with G4MSF/P on 16 Feb 2011 at a distance of 11.6 Km.

My third QSO was with M0DTS/P on 25 Feb 2011 at a distance of 53.8 Km.

Improving again my 4^th QSO was at a distance of 65.3 Km with M0DTS/P on 8 April 2011.

This picture is a little blurred but shows my “sighting aid” of Durham Cathedral and to the left the red light of Rob’s signal at Danby Beacon on the N.York Moors. I was located at Charlaw Fell near Sacriston in Co Durham.

A portable expedition to the Kings Arms pub at Seaton Sluice on 23 Nov 2011 has yielded another two and a half contacts.

An easy 2 way with Stuart G8CYW/P who was co-located, via scatter from a handy sand dune. Path length of only 0.3Km but useful confidence check of the kit.

A one way receive only at my end of Bernie G4HJW/P baseband signal. Bernie was located near Shilbottle in Northumberland, a path length of 33.3 Km.

The final contact with Gordon G8PNN/P who was also co-located with Bernie at Shilbottle resulted in a more difficult 2 way. The issue was with my transmit not being correctly aligned but Gordon’s signal was easy copy on my receive system.

This has prompted me to get going on full transceive using a single optical device to eliminate the squint issue.

Another excursion to the Durham countryside on Monday 5 March 2012 has yielded another two contacts on optical. I was located near Kirk Merrington with Nick G4KUX. Rob M0DTS and Clive G4FVP were located at Swainby in North Yorkshire. Path length a modest 37 Km, in fact a repeat of my first ever optical two way QSO with Rob.

Objectives were to prove my newly constructed tranceive head and also to confirm operation of Clive’s kit. First QSO with Rob was OK but receive levels using my new head were poor. Rob also had poor receive on his combined head and reverted to his receive only head. The second QSO with Clive was a little more difficult and I had to also revert to my receive only head to complete. By ear I estimate that the receive head is 6 dB or more down on the tranceive head despite optimising the bias for best recovered signal.

I will now change the Golden Dragon led in my head to one of a different batch to see if there is any improvement.

Equipment

All current activity is based on LED transmit heads and either photo diode or reverse biased LED’s on receive.

Signal is produced using a transverter design by Stuart in which the signal is produced at 3605 KHz using a conventional amateur band transceiver, mixed with a local oscillator on 3580 KHz to produce an electrical signal of 25 KHz – this then is used to modulate the red light produced by the high power LED.

A suitable optics system is then used to launch the signal, there are two methods used at the moment – standard 100mm lenses or A4 size Fresnel lenses.

The picture shows my “Two Pipe” system mounted on a tripod. The RX is on the left and the TX is the illuminated lens on the right. The red light is produced from the LED in receive mode.

The small gun sight is used to line up in daylight, it is pretty useless in the dark due to its small aperture lens.

I have since fitted a single 8 x 21 binocular to assist with line up and it’s much more effective in the dark.

Adjusting for azimuth is tricky, very small adjustments at a time with the platform clamped firmly on the tripod. I use a small spirit level to ensure the platform is level.

2012 Update – I have now built a combined transmit/receive head using a “Golden Dragon” LED.

As can be seen above it is mounted on a standard waste pipe end cap and fits directly on to a single pipe containing a single 100mm diameter lens. The Golden Dragon LED was sourced from China via eBay and came ready mounted on the circular board. A quick cut with a scalpel and the protection diode was disabled to allow reverse bias on receive.

The head circuitry is the LED Tranceiver Head Mk2 by G8CYW and is used with the optical transverter. Reverse bias for the diode is provided with a bank of 12V batteries and an adjustable resistive potential divider to provide the 43V (or so) bias. To prevent battery discharge an on/off switch is fitted. There is also a high/low power switch for transmit which switches in the required dropper resistor. The two connectors are for the connections to the transverter (TX and RX/PTT lines).

This head was used for the first time on 5 March 2012 for two QSO’s but unfortunately the receive performance is not as good as the previous photodiode system. Transmit performance is good as expected.

I intend to remove this Golden Dragon and replace with another sample from a different batch gifted to me by Stuart G8CYW. Watch this space!

Future Plans

Members of the group are keen to achieve greater QSO distances, having already broken the 100 Km limit and are always looking for suitable sites to try.

Also being investigated are transceiver designs and sighting aids - beacons.

One member (M0DTS) has already had test transmissions of amateur television going on light!

More info to come.

If you are interested in this mode have a look at http://groups.yahoo.com/group/UKNanowaves/ for further useful information.

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