Phlatlights

In 2012, I bought several of these from the USA. My intention was to use these very powerful LEDs in my experiments with 481THz light communications over the horizon having had great success with QRSS over the horizon with far less powerful LEDs. 

Then I had my stroke and I was just too wobbly for field work. They are still in the shack drawer! It would be great to use these as I am sure much further non line-of-sight would be possible.

Phlatlights

When I have repeated my over-the-horizon NLOS optical (red LED) tests at 481THz using LEDs bought from Hong Kong, I must remember to try my Phlatlights which are about 10dB stronger.  I bought these nearly 2 years ago and have not yet fired these up! The ones I have already have heatsinks so it should be quite easy to use these for QRSS3 tests. In theory it should mean aiming a little less critical or greater range when "on-beam".

At 8.7km over the horizon with a clear sky, QRSS3 signals were about 10dB S/N with the 10mm HK LEDs, so with Phlatights and the same optics (100mm lenses) signals should be much stronger. More tests for when I am fitter.

Over-the-horizon on 480THz

My order for 3 off 12W red LEDs known as PT54 Phlatlights has arrived. These are VERY VERY bright LEDs mounted onto substantial heatsinks which emit a strong signal on 480THz. They were originally intended for portable projection systems. One of mine is going into my QRO optical beacon running continuous carrier, CW, DFCW, QRSS3 or QRSS30 to use in further over the horizon (non line-of-sight) beaconing tests using the scatter from particles in clear air and the reflection off the base of clouds. Last winter my own simple beacon running at around 300mW was detected several km over the horizon using QRSS3. G4HJW's optical beacon using a Phlatlight LED was detectable in my village some 8-9km over the horizon. In neither case could the red glow from the TX be detected by eye.  This week I also received some SFH213 10 degree half angle PIN photodiodes which should be considerably more sensitive than my BPW34 detectors currently in use. Estimates suggest at least 6dB more sensitivity.

Together, the QRO optical beacon running from home, focussed with a 100mm lens (gain about 24-30dB), and a portable high sensitivity 100mm lens based detector should allow plenty of scope for innovative NLOS tests on dark winter evenings.

Just realised: 5W out (for example) into a 30dB gain lens "antenna" is equivalent to 5kW of light power in the beam. That is SOME bright light. Clearly great care is needed in siting and aiming such a system to ensure safety.

QRO optical beacon for over-the-horizon tests

12W red LEDs for optical beaconing

This afternoon I ordered 3 off 12W red LEDs, called a Phlatlight PT54, from the USA. These were originally designed for use in projectors and are VERY bright indeed (425 lumens at 8.1A!).  My plan is to use one of these in my new 481THz optical CW/QRSS beacon for over the horizon non line-of-sight (NLOS) tests this winter.  If you are interested, look up item 170884888890 on eBay. The datasheet for the Phlatlight LED is available at http://www.mouser.com/catalog/specsheets/pt54phlatlight.pdf .

My original beacon circuit is shown below and was a good signal over the horizon 3.6km from home when using Spectran to show the received signal, which was not even visible to the naked eye or audible in a headset. I am hoping that a very similar circuit will work for the Phlatlight LED beacon.

The QRO beacon should be much stronger, so I am expecting to be able to achieve much greater NLOS ranges, especially as my receiver is capable of considerably greater sensitivity with more work and using better PIN photodiodes with a more optimal 3dB sensitivity angle. The main issue is a thermal one: although the device is mounted on quite a good heatsink, I need to find out how hot this gets when sending CW or QRSS and derate it accordingly. I am hoping that around 4-5A should be possible which should allow some 20dB more output.