Is ducting possible using Luxeon LEDs ?

[VK4QB]

Hi All.
Food for thought !!! . If the luxeon LEDs can get 100 k without ducting, may be they can be treated like 1296 Mhz etc and get across the Great Aussie Bight ? Anyone got any guesses?
Brian 4QB

[VK2KRR]

Hi Brian
Maybe check out my webpage on Atmospheric Optics http://www.users.bigpond.com/vk2krr/atm ... optics.htm
Post more of my thoughts after work.

[VK2KRR]

HI Brian

In my view I feel its possible to duct light waves 2000 Km, BUT the only problem is the natural atmospheric properties required to support it would probably never occur. But in theory yes. Over long distance though you gotta keep in mind and number of attenuators of light, dust, pollution, water particles etc. Also I think being at the correct height to get light into a duct would be critical and also the receiver would need to be at the correct height and looking in the right direction.

For example at my QTH, the rare times I get superior mirages on the horizon, I only have to travel down hill a bit and eventually the mirage image is no longer visible. I have not really tried it in the other direction, ie increase height.

There is a person called Andrew Young who was been studying mirages and light propagation, he requested a link from his page to mine for people to view the mirage images Ive taken. On Andrews page http://mintaka.sdsu.edu/GF/mirages/mirintro.html he has some info and diagrams that you may find very interesting regarding light propagation.

[vk6zry]

One would have to work out at what wavelength to transmit. One might imagine green would be better than red and perhaps blue which is shorter. If Luxeons have been used at line of sight, you have to know they are made of the 3 primary colours. That is red, blue and green to produce white visible light, maybe with a bluish tinge.
Ask yourself why is the sky blue? hahaha
Find out what wavelengths are absorbed the most, starting with red and ending with blue.
I suggest a cheap green laser at 7.5 mw available from Jaycar, and feed it with 4.5Volts, 3 AA batteries work quite well, then glue a mirror onto a speaker diaphragm. Using a 1.0 KHZ tone driving the speaker reflect the laser beam off it.
A reciever could be a photo transistor with associated amplifier/speaker, the photo diode could be the focal point of a large
plastic Fresnel lense.
Using the green laser as a source pointed at let say a distant cloud or hill, then try the reciever, listening for the one kilohertz tone.
If you point the reciever at a passing jet you might be suprised at what you hear.
Line of sight - great, ducting - doubtful. Ask yourself have you ever seen a distant city or town's lights via duct?
In the west the guys transmitted on 10.5GHZ 400kms across the sea, provided they were on the beach lesss than 2m
above the water. I wish they had one of those green lasers then.
Goodluck, the State governments/police (helicopters) abhor them nasty green lasers.
What you need is a remote beacon/source of modulated light and with your remote reciever get a logical result.
cheers from Sunny Perth.

[VK4DDG]

Hi, I was told by a Ex QANTAS 747 Captain who is also a Ham that on aproach to Auckland airport one night they were seeing a very bright flashing light on the horizon and had no explination for it, they timed it and found it to be the same timing as Cape Byron Lighthouse? (Australia's most easterly point) That made perfect sence to me, as i spent many years at Byron up on the first ridge inland and had many many qso to ZL as VK2DDG on Tropo ducting.. My guess is that the MUF was way up there that night. And Yes i recon it is possable and has happened before but only very ocassionally..Tom

[VK4QB]

Hi Tom,
Thanks for that interesting snippet. Usually ducting in the lower atmospheric level can be seen, It usually occurs due a change in temperature such as caused by a cold front, or a temperature inversion. This will cause the VHF, UHF microwaves and light to be ducted along a path parallel to the earths surface, for some distance much more than normal. I have seen 30 cm radar get an island target about 50 miles range from water level before we could see the object by eyeby ducting. This indicates that it can varying its reflecting it properties or altering its frequency reflective properties. . The quantas captain probably was at a height that he ran through the ducting area. Evidently the duct can be a any height and not necessarily from ground level upwards. The duct could conceivably been skewed upwards too. like the duct at Byron Bay could have been from ground up to say 200 feet and the duct at Auckland could have been much higher. Its a bit hard to chase ducting conditions to find out just what is happening, but we know they are there.!
73
Brian 4QB .

[vk2xso]

The phenomenom where light is ducted is called a "superior atmospheric mirrage or image".
There are two types that I'm aware of. A ducted image seems to keep it's orientaion usually with some distortion that looks very much like a mirrage, while reflected images appear inverted, like a mirror in the sky. Again the image tends to shimmer and distort.
These superior images might also explain some UFO sightings. I've seen one that was a container ship that looked like it was floating through clouds.
I've only heard of the other kind. An example would be a very sharp high inversion layer in the Tasman sea and people on the east coast of Australia looking out to sea and seeing parts of New Zealand hanging upside down in the sky.

edit - doh ! just noticed Leigh's page.

After seeing Andrew's mirage page, I'm just going to pack up my telescope and PMT and go back to radio.
I'm having a brain meltdown just trying to soak up all the information and fantasic pictures.