cw using light? - AR15.COM

Posted: 2/25/2017 7:28:19 PM EDT

a guy at work got a super bright laser pointer. like uber bright. anywho, he says he's going to try to attach it to a transmitter and see if he can transmit cw, then voice. His concern is finding a photocell sensitive enough to work at distance.

discuss.

ETA: he said something about trying IR also

Posted: 2/25/2017 7:41:27 PM EDT

[#1]

Quoted:
a guy at work got a super bright laser pointer. like uber bright. anywho, he says he's going to try to attach it to a transmitter and see if he can transmit cw, then voice. His concern is finding a photocell sensitive enough to work at distance.

discuss.

View Quote

Define "at distance".

Sensitivity should not be a problem, as there is very little attenuation of laser light over distance.

I seem to recall that people were doing this 60+ years ago with flashlights, just as a point of interest.

Posted: 2/25/2017 7:47:33 PM EDT

[#2]

CW shouldn't be a problem as it's just on or off. Voice is another matter as you would have to modulate the light source (laser) somehow unless you convert the audio to a digital signal then transmit the digital signal with the laser. Then you will need a way to turn the digital signal back into an analog signal to hear it on the receiving end.

Posted: 2/25/2017 7:58:34 PM EDT

[#3]

Live video over plain old beams of light and at a pretty good bandwidth was transmitted at least 40 years.

meh

Posted: 2/25/2017 8:06:47 PM EDT

[#4]

I agree with the above, fun tinkering but he isn't doing anything new.

Posted: 2/25/2017 8:16:48 PM EDT

[#5]

A signal man aboard LST-782 sends a message off the coast of Iwo Jima, Japan dur...HD Stock Footage

https://www.youtube.com/watch?v=BFwH_zR01-E

Posted: 2/25/2017 8:41:03 PM EDT

[#6]

Two of us transmitted music back in the early '60s using a pilot lamp (no lasers back then) and a vacuum tube photocell. IRC our distance was about 50 feet. We used lenses to concentrate the beam at both the transmitter and receiver. The ambient light de-sensed the photocell, so we used a long focal length lens and blackened tube at the receiver. The frequency response sucked because of the thermal mass of the lamp, but you wouldn't have this problem with a laser.

For CW, you'd probably have better luck if you modulated the beam with a tone, in effect creating an MCW carrier.

IIRC, there have been a couple of articles in QST by hams doing this.

Posted: 2/25/2017 8:42:14 PM EDT

[#7]

.....Wuthering Heights via Semaphore Flags, anyone?

https://youtu.be/kqiUGjghlzU?t=1m3s (guess standard members can't tag youtube vids)

Posted: 2/25/2017 9:09:26 PM EDT

[#8]

My first thought was this old video I have always wanted to try.

Weekend Project: Make a Simple Laser Communicator

https://www.youtube.com/watch?v=HKRPfa66_po

I was talking to some guys in the commercial microwave market that are using laser based radios in NYC for stock trading communications. Their example was "wireless fiberoptic" of course atmospherics play a big part and it is true line of sight, it got some really impressive speeds and latency numbers.

Posted: 2/25/2017 9:17:16 PM EDT

[#9]

What if there is a mountain between the transmitting and the receiving stations?

Posted: 2/25/2017 9:23:34 PM EDT

[#10]

Quote History

Quoted:
What if there is a mountain between the transmitting and the receiving stations?

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I'm a telephone guy, with very limited uhf stuff.

but i'd guess it wont work, like all LOS

Posted: 2/25/2017 9:39:46 PM EDT

[#11]

This sounds like a job for the Navy.

Posted: 2/25/2017 9:57:32 PM EDT

[#12]

Quote History

Quoted:
What if there is a mountain between the transmitting and the receiving stations?

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Same way all other LOS comms would

OP

True or not just wrap your head around this subject. True nerd radio

Quantum Satellite

Posted: 2/25/2017 11:19:01 PM EDT

[#13]

This has been done for a while. The hams doing it prefer LEDs and not lasers.

Check out KA7OEI's optical page.

95 mile QSO's on a 50W red LED is pretty interesting.

Posted: 2/26/2017 1:47:48 PM EDT

[#14]

If he buys lab type lasers I should think most have a modulation input/output. The ones we played with in college did and that was 30 years ago.

It was fun listening to other classes lectures with the reflections off their windows.

The LED thing is very interesting, I may have to pick up some cheap IR LEDs to play with this with.

Posted: 2/26/2017 2:04:58 PM EDT

[#15]

If the laser happens to be at a wavelength that is popular for fiber comms, then there'll be a crapload of optimally sensitive receivers available. If not, well then some interpolation and experimentation may be required.

Naturally, gain at the receiver "antenna" end is good - that means lenses / telescope.

Posted: 2/26/2017 8:18:17 PM EDT

[#16]

Quote History

Quoted:
CW shouldn't be a problem as it's just on or off. Voice is another matter as you would have to modulate the light source (laser) somehow unless you convert the audio to a digital signal then transmit the digital signal with the laser. Then you will need a way to turn the digital signal back into an analog signal to hear it on the receiving end.

View Quote

I've modulated the power supply to a cheap laser pointer by putting an audio isolation transformer in series with the battery, then connecting to an audio source. Crude, but it works.

ETA, I see that youtube has me beat.

Posted: 2/26/2017 9:34:20 PM EDT

[#17]

http://www.amateurradio.com/lightwave-madness/

Posted: 2/26/2017 11:17:03 PM EDT

[#18]

Quoted:
If the laser happens to be at a wavelength that is popular for fiber comms, then there'll be a crapload of optimally sensitive receivers available. If not, well then some interpolation and experimentation may be required.

View Quote

Saying Ubiquiti may have coined the term AirFiber too soon?

Posted: 2/27/2017 2:44:04 AM EDT

[#19]

Quote History

Quoted:

I'm a telephone guy, with very limited uhf stuff.

but i'd guess it wont work, like all LOS

View Quote View All Quotes

View All Quotes

Quote History

Quoted:

Quoted:
What if there is a mountain between the transmitting and the receiving stations?

I'm a telephone guy, with very limited uhf stuff.

but i'd guess it wont work, like all LOS

Cloud reflection, dude!

Posted: 2/27/2017 8:34:01 AM EDT

[#20]

Quote History

Quoted:
What if there is a mountain between the transmitting and the receiving stations?

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You give a guy one of these and put him on top the mountain.

Posted: 2/27/2017 1:01:37 PM EDT

[#21]

Quote History

Quoted:

You give a guy one of these and put him on top the mountain.

https://media.midwayusa.com/productimages/880x660/Primary/198/198617.jpg

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I just put one of those in my boat yesterday.

Posted: 2/27/2017 1:35:35 PM EDT

[#22]

Quote History

Quoted:
I agree with the above, fun tinkering but he isn't doing anything new.

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The photophone is a telecommunications device that allowed for the transmission of speech on a beam of light. It was invented jointly by Alexander Graham Bell and his assistant Charles Sumner Tainter on February 19, 1880, at Bell's laboratory at 1325 L Street in Washington, D.C.

Posted: 2/27/2017 1:40:50 PM EDT

[#23]

Build the long range Laser Spy system

Posted: 2/27/2017 10:48:21 PM EDT

[#24]

Yeah, nothing new but a fun experiment. During the cold war spies used IR laser "radios" to talk to each other LOS.

Can't remember the company now, but there are a few who are making two-way IR laser radios still.

Years ago using free space lasers was an "easy" way to create a data link between two sites.

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