Optical broadcasting

Forum for discussion of electronic television. Generally, stuff to do with CRTs and not using mechanical displays.

Re: Optical broadcasting

Postby AncientBrit » Wed Apr 20, 2016 1:42 am

Okay Steve,

Understood,

Cheers,

Graham
AncientBrit
Green padded cells are quite homely.
 
Posts: 858
Joined: Mon Mar 26, 2007 10:15 pm
Location: Billericay, UK

Re: Optical broadcasting

Postby Brigham » Wed Apr 20, 2016 4:02 am

Panrock wrote:Hi Graham,

Thank you for your comments, supportive as always. Much appreciated though not really earned. And thanks for the tips.

Well, there's now the page at http://www.radiocraft.co.uk/opto.htm of course, though it's a bit chaotic. Also Andrew Emmerson was on the phone last night. He's going to mention it in his regular column in 'Practical Electronics'.

Other than that I'm basically a shy soul and not into 'publicity' as such. I prefer the actual inventing process
.

Cheers,

Steve O


That could be said of JLB as well. His publicity was dire until Sydney Moseley burst onto the scene.
Brigham
"Fester, enough of the light-bulbs!"
 
Posts: 9
Joined: Wed Apr 20, 2011 12:23 am
Location: Co. Durham

Re: Optical broadcasting

Postby Panrock » Mon May 30, 2016 11:26 pm

I have been making some more progress. I am now in the later stages of building an infra-red transmitter (modulated with VHF) with an optical power of around 1 watt. The beam intensity will be equivalent to about 50 watts omnidirectional.

For reasons of optical safety, it will never be possible to demonstrate this at a Convention. Indeed, I have been thinking a lot about safety recently. I have been putting together a 'safety protocol' for workshop practice, which you can read at the bottom of the OPTO page. I invite comments. Be as rough and tough as you like. Better a red face now than a serious accident later.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 831
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Optical broadcasting

Postby Panrock » Tue May 31, 2016 3:37 am

And here's a view of the business end of the 'finished' unit. The 12 highly directional infra-red LEDs are mounted on a PTFE board some way behind an aluminium panel, which hopefully will combine low capacitance with good RF screening.

This won't be switched on until I have my infra-red goggles and even then I'll keep out of the beam's way. I will test the goggles before use with an infra-red-sensitive tv camera.

Steve O
Attachments
8322.jpg
8322.jpg (68.52 KiB) Viewed 8606 times
Panrock
Green padded cells are quite homely.
 
Posts: 831
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Optical broadcasting

Postby Panrock » Sat Jun 11, 2016 4:30 am

The goggles arrived - 4 days from China after promising 2 to 4 weeks - I was impressed - and were duly tested for efficacy on one of the 70mW 850nM infrared LEDs, viewing this through them with an infrared-sensitive TV security camera. Nothing detectable passed through. In fact they also cut out visible red light from 600nM and up, resulting in reds looking black.

The same IR-sensitive camera can be seen viewing the scene in the bottom picture below. Correctly, it shows an intense glare (otherwise invisible though I haven't looked!) coming from the output unit. This is despite it being well off-axis from the beam, and being scattered and absorbed by the internal blacking in the attenuator funnel.

The power of the new unit is 1000x that of the old so demands some respect. Or perhaps 'fear' would be a better word! For initial setting up, I added the previously mentioned blackened front funnel with a small hole in the end, to reduce what gets out. This also makes it very difficult for me to accidentally get in the beam, while wearing the goggles of course. This 'attenuator' started life as a 'Coke' cup.

Does it work? Yes. How well though will become clearer as I tweak and optimise it in the next few days. This rig is less directional than the first. Its aim is to provide data about what power will be required in practice from an eventual infrared 'broadcasting' array having a fan-shaped horizontal polar diagram.

Steve O
Attachments
8350.jpg
8350.jpg (60.53 KiB) Viewed 8582 times
8354.jpg
8354.jpg (92.23 KiB) Viewed 8582 times
Panrock
Green padded cells are quite homely.
 
Posts: 831
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Optical broadcasting

Postby Panrock » Sun Jun 26, 2016 10:33 pm

The latest news and thoughts can be read here:

http://www.radiocraft.co.uk/opto.htm#latest

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 831
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Optical broadcasting

Postby Steve Anderson » Sun Jun 26, 2016 11:18 pm

Thanks for the update notification Steve. Shame about the amp module(s). Oh well, these things happen.

Steve A.
User avatar
Steve Anderson
"Fester! Don't do that to 'Thing'"
 
Posts: 3793
Joined: Fri Mar 30, 2007 10:54 pm
Location: Bangkok, Thailand

Re: Optical broadcasting

Postby Panrock » Mon Jun 27, 2016 7:57 pm

They do indeed... especially when I'm involved!

Thanks for your interest. Like all such projects, it's just a case of plugging on with it. I learn as I go, and change course to siddle round the next obstacle as necessary.

Steve O

P.S The link at http://www.radiocraft.co.uk/opto.htm#latest will be shifted down the 'Opto' page at regular intervals so it points to the very latest content. That's the best place to go if you want to keep up with this project.
Panrock
Green padded cells are quite homely.
 
Posts: 831
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Optical broadcasting

Postby Panrock » Thu Jul 07, 2016 1:59 am

Well, I've just 'siddled' round another obstacle. I've decided the rig above is pointless and a blind alley.

On reflection, it seemed to me the best way to build up the big system would be to do so progressively, in stages. Make a small system 'cell' first and then multiply them, linking more and more together until I'm where I want to be.

To this end, I have just put together a simple wide band LED driver circuit with a high input impedance using a single fast MOSFET transistor. However, because of the device's 30pF input capacitance, it has to be fed from a low'ish impedance to work at VHF frequencies.

Anyway, this works, and gives excellent results. I am hopeful each of these little circuits can be made to drive a small cluster of LEDs. These 'cells' will then be stacked in parallel, and when the combined input impedance gets too low - another high input/low output impedance circuit will be added at the front end of a new bunch - and so on. In this way a 'nest' of circuits would gradually grow, eventually incorporating hundreds - or thousands - of LEDs.

Because what I am playing with is varying amounts of 45.0 and 41.5 MHz 'subcarrier' on my 'heat beam', which is AC (rather than baseband video, which is varying DC), the picture polarity should not be affected by phase inversions back-and-forth produced by the amplifying stages. It should always look right. So as long as the signal-to-noise stays favourable, I shouldn't have to worry about the number of levels in my 'nest'.

A final system of this type would be broad band, and suitable to provide other services alongside analogue television, from the start.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 831
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Optical broadcasting

Postby Harry Dalek » Thu Jul 07, 2016 11:10 am

Yes Steve the dreaded reboot has struck me many a time as well .
Your new way does sound good you could make the transmitting light levels as large as you wanted with the smaller stages .
I suppose you could switch stages on and off and if one failed you still have the others working .
What distance is you goal line of sight ? reminds me of some others on light transmitting but they never tried wide bandwidth video like this .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
User avatar
Harry Dalek
"Fester! Don't do that to 'Thing'"
 
Posts: 4012
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

Re: Optical broadcasting

Postby Panrock » Thu Jul 07, 2016 2:07 pm

Harry Dalek wrote:Yes Steve the dreaded reboot has struck me many a time as well .
Your new way does sound good you could make the transmitting light levels as large as you wanted with the smaller stages .

The risk is going to be the growth of stray capacitance everywhere.

Harry Dalek wrote:I suppose you could switch stages on and off and if one failed you still have the others working .

Or more likely a stage will 'switch itself off' by failing!

Harry Dalek wrote:What distance is you goal line of sight ? reminds me of some others on light transmitting but they never tried wide bandwidth video like this .

'The horizon' (a few miles) I guess. To achieve this will require some more development at the receiving end too.

I'll never be in the running for directional distance records like Chris Long. Wide band is far too insensitive for usable signal-to-noise. I will not be pointing at anything but spreading the energy all around too. And this is very wide band (VHF radio, not video) so the idea is there'll be room for all sorts of things at once.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 831
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Optical broadcasting

Postby Panrock » Fri Jul 15, 2016 3:24 am

Sod this for a lark! More in the usual place... and it's not particularly good.

I am now looking forward to switching efforts to the Mirror Screw for a while, since a visit from Karen Orton with her new Timing Corrector might now be imminent.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 831
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Optical broadcasting

Postby Harry Dalek » Fri Jul 15, 2016 7:23 am

Panrock wrote:Sod this for a lark! More in the usual place... and it's not particularly good.

I am now looking forward to switching efforts to the Mirror Screw for a while, since a visit from Karen Orton with her new Timing Corrector might now be imminent.

Steve O


Some times it is good to put it away for a while and have a think about if its worth it ,pretty much did what you wanted the distance problem sounds like more money than what you could make Steve.

Whats Karen's Timing corrector ? you should start a topic on it .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
User avatar
Harry Dalek
"Fester! Don't do that to 'Thing'"
 
Posts: 4012
Joined: Fri Sep 26, 2008 4:58 pm
Location: Australia

Re: Optical broadcasting

Postby Panrock » Fri Jul 15, 2016 9:05 am

Harry Dalek wrote:Some times it is good to put it away for a while and have a think about if its worth it ,pretty much did what you wanted the distance problem sounds like more money than what you could make Steve..

Yep, could do with a break for now. Still, I'm learning as I go and just because something's difficult doesn't mean it's not worth it. :wink: I haven't given up. No way.

Harry Dalek wrote:Whats Karen's Timing corrector ? you should start a topic on it .

This is dealt with over on the 'Getting started with mirror screws' thread. Karen's converter will hopefully enable electronic error correction of the slats' positions, essential if we're to use it at 120-lines.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 831
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Re: Optical broadcasting

Postby Panrock » Sun Jul 17, 2016 2:35 am

Right. I've now re-booted the project (can't leave it alone!) and set out a new possible way forward.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 831
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Previous

Return to Electronic NBTV

Who is online

Users browsing this forum: No registered users and 2 guests