Optical Communications

It is many years since I tried any optical communications, because of my poor health:  I have been too giddy for field work.  

Hopefully, the next few weeks will allow me to do some local tests from home.

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

Light wave communication

Yesterday I mentioned that some years ago I bought some Flatlights (very high power LEDs) to allow me to get further over the horizon with light beam communication. Even with quite low powered LEDs I was able to achieve quite decent ranges non-line-of-sight. 

Optical communications is accessible to all and is ideal for homebrewing. All my gear was homemade and all software was free. Also, only very simple test gear is needed. As I recall a multimeter and a bearly lit LED in a dark room is about all you need. This is much simpler than microwaves. 

There is so much to be learned about optical communications. My "thing" was detecting weak signals over the horizon using PC software. What amazed me was there was no sign of the light in the sky, yet the signals were perfectly detectable on the PC as long as the RX was aimed in the right direction. I am sure much further would have been possible.

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

481THz experiments

Many years ago before my 2013 stroke I bought some Flatlights (very bright LEDs) from the USA to enable me to get further with my optical experiments over the horizon. Even with quite low power LEDs I had got way over the horizon. 

Both my RX and optics could have been improved, so I was expecting much greater ranges. Then I had my stroke and I was unable to continue. To this day the Flatlights remain in the drawer unused.

Optical communications

Optical RX

Until my stroke in 2013, one of my joys was building and testing optical communications gear. Although I had a successful line-of site speech contact, my "thing" was weak signal communication over the horizon.

Even without any visible signals in the sky I was able to detect my beacon from home on 481THz (red optical) way over the horizon, even though it was firing through double glazing. Had I been able to carry on, there were so many things I wanted to try including higher powerLEDs, further distances and a better tripod.

Sadly, these days I am too wobbly to do this portable work. As all the gear can be built and tested in the "back of a garage" with simple test gear, this could appeal to those interested in serious, but low cost, experimentation. Over the horizon optical work could do with attention.

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

481THz speech communications

Long before my 2013 stroke, one of my favourite things was optical communications.

Although my keenest interest was weak signal "over the horizon" signals, so called non line of sight (NLOS), I had one QSO with speech over a path of about 11km with G4HJW using the kit shown in the photo. Sadly my stroke put an end to my optical experiments.

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

481THz RX

Whilst looking through some old Google photos, I came across this one of my 481THz (optical) receiver. It was used in my "over the horizon" tests. It was also used in a line-of sight optical speech QSO over 11km with G4HJW.

I still have it and should try using it again.

Good optical comms site

On my own main website is some information (now very dated!) about my own experiments with optical communications at 481THz (red light). I was mainly interested in over the horizon, weak signal modes.

I was quite amazed to clearly detect my optical beacon over the horizon when nothing was visible in the sky. There were no clouds so I assume this was clear air scattering off dust particles.  This was using QRSS3 and a PC to "see" the signal. My own experiments stopped shortly after my 2013 stroke. I did try one experiment out portable since, but I was too clumsy. I have not tried anything portable since 2014.

All the gear needed is quite simple to make and all the test gear needed easy to fabricate. I made a very weak signal source using a very very dim LED to test the receivers. This was mounted near the ceiling of a darkened room. With a good RX this should be received OK. If you cannot detect modulation on a very dim LED your RX is not good enough.

I still have all my optical kit. If anyone local wants to borrow it to carry on the experiments, I'd be very happy. They must be local as I will want the gear back.

Another good resource is http://www.modulatedlight.org/optical_comms/optical_index.html

Optical DXing

Since my 2013 stroke I have not felt fit enough to do field work. I really miss my 481THz over the horizon NLOS (non line of sight) optical work.

Testing the optical kit

The results back in 2013 suggested much further would have been possible NLOS. All the gear was home made and the experiments were fun. Sadly I am just too wobbly these days.

It would be good to try infra-red frequencies. What amazed me was the total lack of a visible signal, yet perfect decode using QRSS3 on the PC on a very non line of sight path over the horizon.

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

Optical kit

One of my Facebook memories today is of testing my 481THz optical kit in the garden of the old QTH. In those days I was fit and well. These days, field work has proved impossible although I still hope to restart one day. The photo is here as a reminder (to me!).  And, no, I was not looking at that attractive girl up the street!

All the optical kit was homemade and easy to assemble and test in the back of the garage with very basic test gear. Even the software used was free. Over the horizon testing with optical kit was challenging and great fun. Results amazed me.

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

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...