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Join Date: Jan 2012
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Laser Communication

04/03/2012 2:39 AM

sir, if i am using light as a carrier for modulating a TTL electrical signal which modulatiion does it occipy?

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#1

Re: laser communication

04/03/2012 3:56 AM

Pulse?

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#2

Re: laser communication

04/03/2012 4:02 AM

Amplitude?

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#3

Re: Laser Communication

04/03/2012 4:04 PM

Width?

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#4

Re: Laser Communication

04/04/2012 12:22 PM

Frequency modulation?

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#5
In reply to #4

Re: Laser Communication

04/04/2012 12:52 PM

Dunno if you can do that with a laser

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#6
In reply to #5

Re: Laser Communication

04/04/2012 1:03 PM

Good point. I'm pretty sure it could be done within limits but I was actually thinking of frequency modulation of a carrier (clock) signal.

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#7

Re: Laser Communication

04/05/2012 9:44 AM

Hi there. It is not amplitude modulation. Since the TTL signals are fixed width (?) then I figure it should be frequency modulation.

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#8
In reply to #7

Re: Laser Communication

04/05/2012 10:35 AM

As can be seen from all of the guesses about the type of encoding, perhaps a little basic research into the respective responses would help answer the question.

With digital signals the information can be impressed upon several methods of transmission. Generally the least expensive is usually the one taken unless there are security issues. That being said, it also helps to understand whether a clock signal is superimposed with the information. Without the clock signal, the receiver would have to be setup to operate at very near the same frequency in order to keep synchronization (as in asynchronous serial communication).

For all anybody knows, it could be simple form of RS232 without the wires. But it sounds like it only goes one direction as in simplex communication.

I doubt frequency modulation is the method. True FM by definition requires changes in the laser light color. Not a likely method. It is probably just on and off as 1 and 0. But a dual tone type of transmission has also been used for serial data. The higher frequency tone represents a "1" and a lower tone represents a "0".

In a case like this, you need to know what is possible to recognise it.

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#9

Re: Laser Communication

04/06/2012 6:08 PM

In 1970 I did amplitude modulation of a 6328 A laser beam. In the same period, there were methods to FM and PM of the laser. See a NASA article:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670008029_1967008029.pdf

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#10

Re: Laser Communication

04/07/2012 10:40 PM

Amplitude , PWM, or OOK.

Right, FM is not possible or practical, neither is phase, unless you have a LOT of money.

PM exists, but $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ (or hold down the key combination for your currency in your Nation)

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