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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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4th Apr 2019, 9:05 am | #21 |
Nonode
Join Date: Jun 2016
Location: Bognor Regis, West Sussex, UK.
Posts: 2,288
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Re: Television over a light beam
I also tried sending audio via light beam in my youth, I used an OCP71.
Actually I could not afford to buy an OCP71 so scraped the paint off a normal OC71. This was an accepted trick until Mullard got wise and filled OC71s with opaque goo to prevent this and maintain the price of OCP71s. Peter |
4th Apr 2019, 9:51 pm | #22 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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Re: Television over a light beam
Yes, we also used an OC71 without it's black cloak. We used to look at the Mullard data books and wish for an ORP12 but funds back then were limited for a 13 year old.
We used to get our transistors out of Decca Radar's dustbins just off the Kingston-by Pass near the school. They were always OK but I suspect were 'blanket changed' when Radar units were being overhauled. Such fun! John. |
5th Apr 2019, 12:20 am | #23 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,676
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Re: Television over a light beam
About the 7th image on this page: Radio Love, using a laser modulated with RF sub-carriers.
http://www.modulatedlight.org/Modula...Amateur79.html I clearly remember that diagram and the accompanying story in the radio press at the time (probably PE or PW). I doubt if it amounted to more than a proof of concept. The parent page is http://www.modulatedlight.org/Modula..._LIGHT_DX.html and I am sure somewhere in that lot are some recordings of Australian amateurs in cross-band RF<>light QSOs and one amateur that applied for, and received a letter of variation that left no doubt that his modulated light operation was legal.
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5th Apr 2019, 3:22 am | #24 |
Nonode
Join Date: Feb 2005
Location: Worcestershire, UK.
Posts: 2,525
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Re: Television over a light beam
Here's a little thought experiment. Take a RF modulated light system. Amplitude-modulate this with a signal containing very low audio frequencies. Can the light be seen to flicker?
Steve |
5th Apr 2019, 4:28 am | #25 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
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Re: Television over a light beam
Nothing should be visible except as a strobing if another ac light source is present. The
problems that occur in a basic AM system mean that whether the modulating signal is analog or digital, PWM is better, and it's the ability of the modulator to respond to signals up to the upper video range that limit its usefulness. Although IR is preferable to white light, I suggest that transmit/receive on RF say, 5.8GHz is easier, remodulating back to VHF at the local set. |
5th Apr 2019, 10:22 am | #26 | |
Rest in Peace
Join Date: Jul 2011
Location: Bridgnorth, Shropshire, UK.
Posts: 787
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Re: Television over a light beam
Quote:
See you tomorrow, Steve. It'll be good to see friends again. |
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5th Apr 2019, 1:19 pm | #27 |
Nonode
Join Date: Feb 2005
Location: Worcestershire, UK.
Posts: 2,525
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Re: Television over a light beam
Another way to look at it...
Take a System A 405-line television signal generator supplying baseband video. Connect the output to a suitably biased LED. On your generator, select a White Bar signal for a few seconds and then follow up with Black Level-and Syncs. The DC content would vary dramatically between these two signals. The LED's average brightness would change noticeably between the two states. But what if you were to repeat this, modulating your ready-illuminated LED with a 45 MHz carrier modulated in turn with the same two signals? (All AM and DC coupled). Looking at the LED, what would you see? (Naturally I have tried this!) Steve Last edited by Panrock; 5th Apr 2019 at 1:30 pm. Reason: Clarity |
5th Apr 2019, 4:15 pm | #28 |
Heptode
Join Date: Jan 2008
Location: Shrewsbury, Shropshire, UK.
Posts: 824
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Re: Television over a light beam
I seem to recall that there was a commercial system using I.R.
It used FM modulation. I worked in both A/V & broadcast technologies, & I think we used to hire out such links for short-range use. This was for 625-line analogue, together with an audio channel. All your latest experiments sound most interesting, Good luck! David. |
5th Apr 2019, 5:04 pm | #29 |
Nonode
Join Date: Feb 2005
Location: Worcestershire, UK.
Posts: 2,525
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Re: Television over a light beam
Time for the answer. Yes folks, I tried it.
In fact you can fill your light beam up with all manner of RF frequencies, bearing as many sudden DC modulation shifts as you like, and the appearance of the hosting beam will remain tranquil and unchanged. After all, there's either 'more RF' or 'less RF' within it according to the amplitude modulation. In a way, the light beam plays a part just like 'space' does for the orthodox radio spectrum. Steve Last edited by Panrock; 5th Apr 2019 at 5:18 pm. |