Modulated Light - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Graham G3ZVT · 4th Oct 2023, 12:20 am

Quote:

Originally Posted by Oldmadham

Quote:

Originally Posted by dave walsh

I thought this would turn up as a companion piece to the ground sourced transmissions. Sort of a next step up from Telegraphy earth returns perhaps

There was a modulated light design in Practical wireless I believe, using a photo cell and a car headlight. I think some people were sending messages across London by light beam but not very far.

There was a bit of a panic on with the govenment re "Pirate" [Independent] radio at the time. Tony Benn was head of the Post Office and it's regulatory function. The background was the mid sixties and the "summer of love!" Mr Benn had been quite popular with young people and was seen as a modern relatively progressive person, so it was a bit of a disappointment when he sought to introduce a new Bill through Parliament for an Act restricting anything percieved as a threat

.

It seemed a bit of an over-reaction. A bit like most forms of prohibition when things [eg alcohol] just go "underground" [no technical pun is intended!] To my recollection, they were so spooked by these innocent experiments that the law was changed to cover ALL types of broadcasting, not just conventional radio transmissions

t.'

Dave W

I recall seeing an article in a local (Oz) publication about a proposed version to be used for (the proposers hoped) license free broadcasting in the UK .

An "artist's conception" showed a quasi-omni-directional setup which a "consortium" proposed to put (in the first instance) on top of a tall London building.
It was a rather "flying saucer" like contraption, using an array of the (then) latest fad------lasers!

The article was most concerned with the regulatory aspects of this, which a few moment's consideration revealed to be a somewhat "hare-brained" scheme.
It looks like the UK govt of the day took it seriously.

That story was also carried by at least one magazine over here, and if you recall, the station was to be called "Radio Love" so fits very nicely with Dave Walsh's comments. I also seem to remember that the station when demodulated was to consist of several AM subcarriers in the MW band.

Like you I always thought it was no more than a concept.

<Edit>
Follow the links in one of my own posts from 2019.
https://www.vintage-radio.net/forum/...9&postcount=23

Nickthedentist · 4th Oct 2023, 11:20 am

I'm sure I've seen (recentish) "wireless" stereo headphones designed for TV use which were IR.

colourking · 4th Oct 2023, 12:28 pm

Quote:

Originally Posted by Nickthedentist

I'm sure I've seen (recentish) "wireless" stereo headphones designed for TV use which were IR.

Yes came across one of those some years ago, a Clatronic KHI271 cordless IR emitter headphones unit (that someone else discarded) - I found that it modulates the IR for the stereo Left channel at 2.3MHz (approx) and the right channel at 2.8MHz approx WFM.

A scanner in WFM mode (for FM broadcast) could pickup some RF radiation on those frequencies in the vicinity of the IR sender and clearly demodulate the audio. I also found a mixture of both L and R channels appeared on 5.135 MHz (2.308 MHz + 2.826 MHz ).

So any SWLs/ DXers who pick up what appear to be mysterious WFM signals on HF (a wide unintelligible distorted mess on AM receivers) ? - have a look around for any nearby IR headphone senders!

Graham G3ZVT · 4th Oct 2023, 1:38 pm

I had an IBM Thinkpad laptop and a Sony Ericsson mobile phone that linked up via IR, at GPRS
speed, or EDGE if the wind was blowing favorably.

Herald1360 · 4th Oct 2023, 9:11 pm

Quote:

Originally Posted by dave walsh

......

There was a modulated light design in Practical wireless I believe, using a photo cell and a car headlight. I think some people were sending messages across London by light beam but not very far.

.......

Dave W

ISTR the modulation method for the headlight beam used a couple of cardboard gratings (cornflakes packet comes to mind in my version) and a loudspeaker. One grating was fixed and the other attached to the centre of the cone (voicecoil). They were mounted with the slits half overlapping so movement of the grating attached to the cone modulated the light intensity.

The frequency response and range were somewhat better than the directly driven torchbulb approach!

stuarth · 5th Oct 2023, 10:12 am

Far too many years ago, while I was in 6th form, (late 1960’s, before all this new-fanged men on the moon and supersonic passenger jets), I put together a fibreless optical link for display in the physics lab for a parents open day.

The transmitter was a cycle lamp with a Mullard 5-10 connected across the top where the switch should be. The 5-10 output transformer provided the DC path to light the bulb (DC bias, essential). Drive levels so the bulb was just flickering on music peaks were about right.

The receiving device was solid state, based on an OC71 with the paint scraped off, I had some old stock from before Mullard started using opaque jelly to foil the use of a paint scraper to impact sales of OCP71. Can’t remember what the lens on the receiver came from, but it was about the size of the cycle lamp reflector. Sound quality wasn’t too bad, no sparkling treble, but nothing anybody commented on.

It was inspired by something in a magazine, probably Radio Constructor.

Oh well, at least modulated light is still with us.

Stuart

bigfathairyvika · 5th Oct 2023, 11:07 am

Not sure if it's still operational, but there used to be a modulated red light morse beacon on top of RAF Wyton water tower in cambridgeshire.

Andrew2 · 5th Oct 2023, 11:39 am

A couple of us tried light comms a few years ago. The transceivers were simple AM baseband things using 1-watt Luxeon LEDs. No FM subcarriers or SSB, just AM. After an initial 'try-out' over a 3 km path, we next tried over a 10 km path with success. On this second occasion there was a lot of mist in the valley between our hilltop sites and this seemed to cause rumbling effects, but comms were 100%. The lenses were pinched from poundshop magnifiers, and turned out to be pretty decent, genuine glass.
Photos attached. Those are my Binoculars of Doom.

m0cemdave · 19th Nov 2023, 11:36 pm

Some further information on light beam communications can be found via this page and its associated links.

It can be seen that the original WW2 Lichtsprecher concept was further developed by the Eastern version of the Zeiss company during the Cold War and used for secret agent contacts.

Also the Americans had their own verson, for the same purpose.

https://www.cryptomuseum.com/covert/opto/index.htm

4th Oct 2023, 11:20 am	#22
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,571	Re: Modulated Light I'm sure I've seen (recentish) "wireless" stereo headphones designed for TV use which were IR.

4th Oct 2023, 1:38 pm	#24
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,586	Re: Modulated Light I had an IBM Thinkpad laptop and a Sony Ericsson mobile phone that linked up via IR, at GPRS speed, or EDGE if the wind was blowing favorably. __________________ -- Graham. G3ZVT

5th Oct 2023, 10:12 am	#26
stuarth Heptode Join Date: Feb 2010 Location: Heysham, Lancashire, UK. Posts: 628	Re: Modulated Light Far too many years ago, while I was in 6th form, (late 1960’s, before all this new-fanged men on the moon and supersonic passenger jets), I put together a fibreless optical link for display in the physics lab for a parents open day. The transmitter was a cycle lamp with a Mullard 5-10 connected across the top where the switch should be. The 5-10 output transformer provided the DC path to light the bulb (DC bias, essential). Drive levels so the bulb was just flickering on music peaks were about right. The receiving device was solid state, based on an OC71 with the paint scraped off, I had some old stock from before Mullard started using opaque jelly to foil the use of a paint scraper to impact sales of OCP71. Can’t remember what the lens on the receiver came from, but it was about the size of the cycle lamp reflector. Sound quality wasn’t too bad, no sparkling treble, but nothing anybody commented on. It was inspired by something in a magazine, probably Radio Constructor. Oh well, at least modulated light is still with us. Stuart

5th Oct 2023, 11:07 am	#27
bigfathairyvika Hexode Join Date: Nov 2009 Location: Cambridge, Cambridgeshire, UK. Posts: 373	Re: Modulated Light Not sure if it's still operational, but there used to be a modulated red light morse beacon on top of RAF Wyton water tower in cambridgeshire.

5th Oct 2023, 11:39 am	#28
Andrew2 Nonode Join Date: Mar 2010 Location: Dukinfield, Cheshire, UK. Posts: 2,019	Re: Modulated Light A couple of us tried light comms a few years ago. The transceivers were simple AM baseband things using 1-watt Luxeon LEDs. No FM subcarriers or SSB, just AM. After an initial 'try-out' over a 3 km path, we next tried over a 10 km path with success. On this second occasion there was a lot of mist in the valley between our hilltop sites and this seemed to cause rumbling effects, but comms were 100%. The lenses were pinched from poundshop magnifiers, and turned out to be pretty decent, genuine glass. Photos attached. Those are my Binoculars of Doom. Attached Thumbnails __________________ Andy G1HBE.

19th Nov 2023, 11:36 pm	#29
m0cemdave Octode Join Date: Feb 2009 Location: Bletchley, Buckinghamshire, UK. Posts: 1,158	Re: Modulated Light Some further information on light beam communications can be found via this page and its associated links. It can be seen that the original WW2 Lichtsprecher concept was further developed by the Eastern version of the Zeiss company during the Cold War and used for secret agent contacts. Also the Americans had their own verson, for the same purpose. https://www.cryptomuseum.com/covert/opto/index.htm