2013 optical tests over the horizon

Before my 2013 stroke I enjoyed 481THz optical tests over the horizon. What surprised me at first was that, even when absolutely nothing was visible in the sky, clear signals could be decoded on a PC as long as the aim was correct. My tripod and aiming left a lot to be desired!  If I was fit enough to repeat these tests I think a much better tripod would be called for allowing better repeatability.

Flatlights

Before my 2013 stroke got in the way, I was hoping to get much further over the horizon with 481THz red light. 

To that end I purchased some very bright LEDs called Flatlights. These take (I am told) 8A from the power supply! The photo show the Flatlight that, sadly, did not get used.

In my earlier tests at just under 9km over the horizon there was no sign at all of a red light in the sky, yet the signal from my beacon was very clear on the PC.  

Even with that, far further would have been possible. As the sky was cloudless, I assume this was clear air scattering off dust particles. I did not try cloud-bounce where signals are reflected off the base of clouds. 

Cloudbounce and scatter optical and IR tests

This morning I read a most interesting article about French cloudbounce and scatter optical tests using lasers. The article is some years old but makes a fascinating read. My own experience with clear air forward scatter at optical frequencies using relatively low powered red LEDs makes me believe that a LOT more is possible in this area. It is a bit like people saying, "UHF is only line-of-sight". Rubbish! With decent, easily built kit it is possible to copy QRP amateur signals over the horizon even at IR and visible optical frequencies.

See http://sd-1.archive-host.com/membres/up/22679775843705539/CBVUK.pdf

Tripods for optical comms

The one I missed on eBay

This evening I was annoyed with myself for not bidding for a tripod on eBay in time that went for just £6.50 in the end.  It had a nice solid structure and a 360 degree marked calibration on the horizontal pan adjustment and would have been ideal for my non line-of-sight optical comms over the horizon, where the ability to return accurately to a know bearing is important when hunting for weak signals.

So, can readers make any recommendations for something similar?
My requirements are:

1. Solid construction so it won't wobble around in wind with the optics and detector mounted on top.
2. Some way of calibrating the direction to within a degree or so horizontally so that known directions can be confidently returned to. Ideally a large 360 degree marked scale.
3. A way for leveling the head assembly so it can be aimed just above the horizon.
4. Low cost as I am looking for an inexpensive solution (don't want the tripod and mount to cost much more than the rest of the kit, which is about £5-10 total!)

Not being a great photographer, I know little about tripods and heads. Looking on eBay I didn't find anything close to the one I missed. It was SO annoying as I only missed it by 5 minutes having been out treating a fence in the (rare) sunshine today.

481THz optical tests over the horizon tonight

This evening I am doing my first "over-the-horizon" optical test this year. The main aim is to check performance with the new receiver and to see how I get on using the iPod Touch 4g running SpectrumView software as the way of seeing the QRSS3 signal. I shall also be taking the laptop running Argo or Spectran.

Latest receiver that seems more sensitive than my older RX

The receiver circuit is the one in Practical Wireless this month by Stuart Wisher G8CYW. This is simple but works well in darkness. I've added an interface to the iPod Touch 4g (a capacitor and a resistor needed to enable the external mic input) and changed the coupling caps and op-amp gain. Using just MPF102 and 2N3904 devices the results look good. The low noise op-amp may be overkill unless one uses super low noise FET and transistor stages too.

After the tests I'll post results in the blog.