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Thread: How far is green beam visible?

  1. #1
    Join Date
    Dec 2007
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    Texas
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    Default How far is green beam visible?

    I ordered a 532nm that puts out around 200-300mW for 10 mins at a time.

    I have been setting up my community for internet service using wireless radios (CPE). There are a couple of customers who are about 1/4 mile or so from the antenna. However, there are a few trees in the way, or rather, the tops of the trees. From their roof, I cannot see my own antenna, and they are getting slightly below average signal strength which lets me know the tops of the trees are in the way. If the whole tree was in the way, they'd have almost no signal. With the terrain, I can't make it out properly by sight alone.

    What I will be doing is around dusk or night, I will point the laser from their roof near the antenna to my access point. I will have an observer on the ground give me an estimate as to how high above the access point the laser beam is just before it is blocked by the trees.

    Even up to 1 mile away, will the beam still be visible overhead? I think the beam divergence is about 0.9 - 1.0 mRad.

    I will be using this for getting line of sight, but I'm wondering if I need this power to get up to a mile of good visibility, or if I went overkill and added unnecessary danger. I don't mind the extra power since it makes the laser more versatile.

  2. #2
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    Aug 2006
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    North West England
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    Default

    If it is just line of sight that you are looking at, why not just look?
    It will be far easier than using a beam.

    Jim

  3. #3
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    Default

    jimbo
    isnt it much more impressive to do this the impractical way with a cool 'laser' beam.
    A pair of binos of a telescope would do best if just looking is a problem

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
    -----------------------------------------------------------------------------------------------
    Laserists do it by the nanometre.

    Stanwax Laser is a Corporate Member of Ilda

    Stanwax Laser main distributor of First Contact in UK - like us on Facebook http://www.facebook.com/FirstContactPolymerCleaner
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  4. #4
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    Texas
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    Default

    The problem is I do NOT have line of sight. Trees are in the way, and I cannot see my antenna. I need to determine how much of the trees are blocking the path, to determine how high I need to mount their antenna. Sometimes I may need to put the customer's antenna 10-20 feet above the roof, which is too high for me to get any line of sight. But I don't want to just put them 20' because of the need to guy the pole, and other wind problems. I want them just above tree level.

    Thus, I aim the laser in toward my antenna until the beam is no longer visible over the destination, and calculate how high I need to raise the customer's antenna to make up for that.

    Plus the laser has that coolness factor as Rob mentioned, that would have customers think that it's pretty neat, even though it might not be as accurate as getting signal strength. If I can create a mounting plate to put over the face of the antenna, then I could get pinpoint accuracy.

    Plus, other people in the community would see the beam and maybe I'd get more customers.

    My questions were:

    1) At 1/4 mile or even 1 mile would the beam still be visible overhead to people on the ground? It's a portable unit with focusing optics.
    2) Is the 200-300mW overkill for this application?


    Quote Originally Posted by JimBo View Post
    If it is just line of sight that you are looking at, why not just look?
    It will be far easier than using a beam.

    Jim

  5. #5
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    Ok to answer your question if there was little or no haze mist pollution etc in the air then probably not very visible if you were directly below the laser beam. You will see a laser beam most clearly when you are looking towards or away from the source at a low angle. Being below the beam you will be at 90 degrees to the beam that you are looking up at. This will not allow you to see much unless it is a powerful laser and/or there is a lot of crap in the air to scatter the beam - which is how we see all light by it being reflected off stuff - in this case particles in the air.

    hope this helps

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
    -----------------------------------------------------------------------------------------------
    Laserists do it by the nanometre.

    Stanwax Laser is a Corporate Member of Ilda

    Stanwax Laser main distributor of First Contact in UK - like us on Facebook http://www.facebook.com/FirstContactPolymerCleaner
    www.photoniccleaning.co.uk

  6. #6
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    Texas
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    Default

    I know that every night I can see the beam of my 5mW pointer clearly, but it's not going 60' overhead. The best thing to do will be to try it when I receive it. I definately need to make a simple mounting plate that can clamp to the antenna when I'm aiming it for exactness.

    Fortunately, it's fairly humid all the time here in San Antonio, so that shouldn't be a problem. If anything, I can mount the laser to a pole and get that line of sight to the antenna, and make it's pitch adjustable. The beam spot would definately be noticable. The beam would be more than 9" wide at this point so this should minimize possible reflection danger.

  7. #7
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    yep you should have no trouble seeing the spot even at this size - obviously the spots brightness and henc evisiblity will be down to how much crap is in the air. If its clear you will get a better brighter spot

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
    -----------------------------------------------------------------------------------------------
    Laserists do it by the nanometre.

    Stanwax Laser is a Corporate Member of Ilda

    Stanwax Laser main distributor of First Contact in UK - like us on Facebook http://www.facebook.com/FirstContactPolymerCleaner
    www.photoniccleaning.co.uk

  8. #8
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    Texas
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    Ok, one other question is will the beam of a 300mW of 532 be visible in an office with standard lighting or outdoors on an overcast day?

    I was looking for a chart that can help me determine mW needed for different effects. I know that depends on beam divergence, air conditions, and such, but just wondering.

  9. #9
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    I doubt you could produce a chart as to quantify something and record on a chart would need you to have knowledge of the air conditions. This is always gonna be a variable and even if there were several charts made based on clear air medium and heavy variants I think its unlikely you could get this to match real conditions.
    In a regular office there is likely to be dust and the like in the air so I would say there is a good chance it would be visible under normal lighting. But as you said yourself its down to divergence power and air quality so its so hard to tell without just trying it

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
    -----------------------------------------------------------------------------------------------
    Laserists do it by the nanometre.

    Stanwax Laser is a Corporate Member of Ilda

    Stanwax Laser main distributor of First Contact in UK - like us on Facebook http://www.facebook.com/FirstContactPolymerCleaner
    www.photoniccleaning.co.uk

  10. #10
    Join Date
    Oct 2006
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    Cleveland, Ohio
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    Default

    One thing to consider is that the trees will keep growing, so 'just above the treetops' one year might be 'FAIL' in a few more.

    Also, it will be difficult to judge how high the beam is from you when you are looking up at it, because there is no reference point, even if you knew exactly what diameter it is. Take the moon for instance.. how it looks larger at the horizon than way up in the sky, because at the horizon you have a reference.

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