Optical Communications

One of my favourite things before my 2013 stroke was experimenting with optical communications. I had some success with "over the horizon" weak signals.  No sign of the red light was visible, yet it could be detected miles away non line of sight (NLOS) with a laptop. These days I am just too wobbly to do this.

As I have said before, test gear is easier than microwaves and all the kit can be made in a shed for very little money. This is an area rich for experiments and right at the frontiers.

See https://sites.google.com/site/g3xbmqrp3/optical .

Commercial optical communications

Many years ago, before my stroke, I did some work at 481THz, red light. I used LEDs as the TX element, but I see that there are some commercial optical links using LASERS. Light has the advantage of being very secure. I expect these commercial units are expensive. My own optical kit was very inexpensive and great fun.

At some point I hope to get back to this work. Amateur optical work is both fun and inexpensive. It is certainly at the frontier of experimentation.

See http://www.lightpointe.com/laser-radios.html .
See https://sites.google.com/site/g3xbmqrp3/optical .

Optical comms at 481THz

It is some years since I last tried optical communications. This has been because of my poor health. 481THz is easy: all gear was home made and test gear is simple. In most ways nanowaves are easier than microwaves. My "speciality" was non line of sight (NLOS) using digital techniques. I also had one 2-way optical QSO over about 11km. Then I had a stroke and everything stopped!

My experiments used low cost red LEDs. At some point I'd like to try infrared. My tripod was low cost. A better one is really needed as aiming is important.

See https://sites.google.com/site/g3xbmqrp3/optical .

Optical Communications

It is some years (before my stroke in 2013) that I last tried seriously with optical communications using red LEDs that I bought at low cost via eBay. These days, I expect a google will bring up lots of links. This is a fun branch of our hobby, with very low costs and lots of homebrewing. This is a branch of the hobby I'd like to try again. There is much to learn.

See https://sites.google.com/site/g3xbmqrp3/optical .

481THz NLOS (over the horizon)

Before my stroke in 2013 I enjoyed building and operating optical communications gear. My stroke has rather scuppered this, for now! Although I had one over 10km line-of sight speech contact with G4HJW/P, my main interest was weak signal, over the horizon, communication. I did tests at over 8km non line-of-sight using QRSS3. Although there was no evidence of the optical signal in the sky, the QRSS3 signal was clearly decoded on the PC at the receive end. Overall, I was left with the impression that much further would have been possible.

At some point I really want to continue this work. All my optical gear was home-made using material that was low cost and easily obtained. Test gear for optical work was simple and low cost too. In my view, optical work is more rewarding than microwaves and the test gear simpler.

See https://sites.google.com/site/g3xbmqrp3/optical

481THz over the horizon

Facebook reminded me that 4 years ago I was doing QRSS3 tests with light at 4.8km over the horizon.

"Much better results this evening with 481THz light beam signals over the horizon at 4.8km. Last night I was 2.5 degrees out and signals were much weaker. Tonight QRSS3 could be comfortably copied at 20dB S/N in 0.34Hz bandwidth. At the receiving end the signal is not audible and nothing visible in the sky from the transmitter. Aiming is VERY critical just above the horizon."

Early lightbeam tests

Waverley Rd, Kingsbridge, Devon, UK

My interest in light-beam communication goes right back to the 1960s when an old school friend and I used a torch bulb as the TX and an OC71 transistor with the black paint scraped off as the RX detector.

One of our first tests was across the street shown in this photo. I lived in the first house on the RHS and we received the test in the house with bay windows on the left. DX was about 25m! We AM modulated the torch bulb biasing it at half rail if memory serves me correctly. It had a very low frequency response as the torch bulb had a poor HF response, as I recall.

We moved to this house in 1959 but the photo is years and years earlier.

Lightwave Comms

Because of my poor health I have not been able to pursue 481THz (lightwave) experiments especially "over the horizon" NLOS tests. Thankfully, others are "carrying the torch" .

See http://qsl.net/ve7sl/westcoast%20lightwave%20project.pdf

481THz experiment - abject failure

Well, I am sorry to report that my 481THz lightbeam experiment was a total failure.

Although I could detect my QRSS3 signal strongly across the house bouncing off the windmill I was unable to detect any sign of the signal at my remote site. I had problems with aiming which did not help, but I was not expecting the total exhaustion this test brought on. In days gone by this would have been easy, but even soldering a headphone jack tired me. Doing the actual test left me totally "done in".  I really should repeat the test with better aiming, but I am not ready in my body.

If one thing this has taught me it is that I am still too feeble for field work. It was a great disappointment, but there will be other opportunities.

In past years I loved doing this sort of experiment. Sadly, my body is telling me, "not yet".

481THz test

The wind is soon to be light and from the north and east. This means our windmill sails will be out of the way if I manage to do some optical tests in the next few evenings. I want to see if I can detect my 481THz red light reflected off the windmill using QRSS3 at a moderate distance.

To do this test I shall need to aim my QRSS3 optical beacon at the windmill and use a PC with Spectran software and sensitive detector and optics at the remote site. I have tripods but they are not the world's best.

As it is some time since I used the gear, I need to do some local tests first to check all is well.

Optical work is fun as all the gear is homemade and test gear is simple. In my view this is more fun than microwaves. It is accessible to all. All you need are a weak light source, a scope, free software and a multimeter.

In my healthier days I had a lot of fun detecting my QRSS3 optícal signal over the horizon  There was no sign of the signal visible by eye, but on the PC screen it was very clearly visible.

See https://sites.google.com/site/g3xbmqrp3/optical/481thz-nlos .

481THz lightbeam experiment?

Our local windmill. Me seated. XYL on RHS.

It is getting close to the time when I fancy some field work! My first experiment will be to detect QRSS 481THz (red light) at some distance by reflection off our local windmill. It will need my XYL to accompany me as it will involve night driving but it will either work or not. This will be my first field test in a long long time.

This picture was taken in 2014 and the laurel hedge has grown quite a bit since. Look at a later post to see how it looks now.
Small steps...

Optical communications over the horizon

I have been too unwell to do this recently, but not long before my brain bleed (Sept 2013) I was amazed at optical communications over the horizon, non line of sight (NLOS) using clear air scattering.

The inspiration for all my optical experiments came from Stuart Wisher G8CYW who did a great series in RadCom a few years ago.

Testing optics

My home made transmitter only consumed about 0.7W from a red LED bought on the internet. My homemade RX and TX used homemade optics based around cheap drain pipes and cheap magnifying glasses. The whole RX and TX were simple and low cost. Only simple test gear was needed too. It is a bit like microwaves, but easier to build and test.

There was no sign at all of the TX beam in the sky.  All alignment used dead reckoning with some panning at the RX end to find the TX.

Using free PC software and QRSS3 helped as bandwidths as low as 0.37Hz were possible.

When fitter I want to try infra-red LEDs instead.

See https://sites.google.com/site/g3xbmqrp3/optical/481thz-nlos.

Optical testing - too easy?

Before dark, I tried TXing from one side of the house to the other reflecting my 481THz optical beacon off the windmill. Even by ear in 600 ohm phones the signal was very clear and very easy to find. This was only about 100m path length, but I wanted to check the gear still worked as it is a long time since I used it. Not sure what to try next as I still feel very wobbly on my feet and tire easily. At least I know my homebrew optical gear all works still.

Next field test - optical?

After my very disappointing results on VLF earth-mode yesterday - I must get to the bottom of why results were quite so bad - I think my next test will be at the other end of the spectrum. We have a windmill very close so I may try bouncing optical signals off this to test my optical gear is working still.   It is a long time since I have done any optical experiments.This will not be too far initially, more a test of the gear before venturing any distance.

Optical article in June RadCom

June's RSGB RadCom carries my article, "Over the Horizon at 481THz" describing my non line-of-sight optical experiments last year. My poor health (stroke) has prevented me doing more with this in 2014. The article was written last year (2013) before my stroke.  Hopefully, a return to good health (by the autumn?) will allow me to continue this fascinating part of our hobby. At the moment I am just too clumsy.

Testing the optical RX

8.5km "over the horizon" NLOS by clear air scattering (in a cloudless night sky) was very straightforward with simple, low-cost optical gear that could be made for next to nothing.  Unlike microwaves, optical kit is very inexpensive and requires only very basic (audio frequency) test gear to set up. Optical alignment is critical and more stable tripods would have helped. 

What amazed me was that nothing was visible or audible at the RX yet the signal decoded and displayed perfectly with Spectran software on the PC.

If you get this magazine, I hope you enjoy the article.  Please let me have any feedback.

481THz RX issue - now fixed

As mentioned in an earlier post, my sensitive non line-of-sight NLOS optical (red LED at about 481THz) RX packed up when I clumsily dropped it yesterday when out in the field at the test site. An investigation this morning revealed a wire had dropped off the battery feed and this was easily fixed. The  RX now works as before.
 
I shall have to try the NLOS test again when my wife can drive me out there. I shall have to do it soon as tree leaves will soon obscure the path at the home QTH end. Just wish I was not so clumsy still following the stroke last year. In the field I feel so much less able than last year. I feel really disabled and hate being so useless and clumsy.

UPDATE 2050z: for now, all my tests will be shack-based because of my poor health, so no immediate plans to repeat NLOS tests until I feel a lot less wobbly.

Non line-of-sight (NLOS) 481THz paths from home QTH

Before venturing out, I have been trying to plot possible NLOS paths with the optical TX at home (inside) and the RX at a convenient roadside spot at a moderate (local) distance. One possible path is VERY remote down very uneven fenland roads which would have to be navigated in the dark with my wife driving the car. I am thinking about her driving the car. I am not allowed to drive as a result of my stroke.  Many of the NLOS paths are blocked by nearby houses and trees. It is a surprisingly hard task.

 Back to Google Earth to see where might be worth trying. From previous tests it is necessary to aim very carefully.

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.

Successful 481THz garden tests

Today I repeated my optical tests across the garden receiving signals on my RX with both 600 ohm phones and Spectran software with QRSS3. This time the tests were very successful with signals at least 40dB over noise when scattered off distant bushes (0.34Hz BW).   I think we are nearly ready for the NLOS tests again!

481THz QRSS3 beaconing across the garden

Last night I fired up my 481THz optical kit with poor results: I think the RX unit may have a flat PP3 battery? On the Spectran display the QRSS3 signal bounced off trees and bushes should be very easy to spot, but for an unknown reason, I was struggling.  I shall recheck all the kit today. The kit has to be well focused and working well to work DX non line of sight (NLOS), which is my plan soon.

My stroke symptoms (poor balance and clumsiness) are really not helping: tasks that were very easy last year are very hard this, well at present they are.  Before my wife and I venture out into the dark fens, I want there to be a good chance of success, which means good and thorough preparation.