29 Sep 2012

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.

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