Laser beam of 30km?

[andreicramp]

Hello,
I just created my account here. I work at a TV&Radio company and I install antennas. I want a gree/red/blue laser, doesn't really matter that can "connect" two antennas. The range of the beam should be seen for about 30km(19miles). Does something like this exist?

Thank you.
also, before you reply, I searched the entire forums and did not find anything that answers my question, so please stick to the topic.thanks

 

[andreicramp]

here's a image describing what am i looking for.

 

[anselm]

Hello and welcome to the forum!:wave:

First of all:
laser beams diverge, meaning they "grow" over distance.
How much depends on the optics used to shape the beam.
There's an inverse relationship between beam diameter and divergence.
You need a very low divergence, so you'd need a relatively large beam diameter to begin with.

Here are some tools to help you calculate that:
gausian beam rev 2.0.xls
pseudonomen137's JScript mRad Calculator
Laser Pointer Divergence Calculator

Typically, laser pointers have a divergence of 0.5~2mrad.

As you can see, getting a "spot" that is not the size of a football field after 30 000 meters
is not a trivial task.


Second:
I imagine it to be very hard to accurately hit a target 30 000 meters away, and the wind
swaying the antenna would throw the laser off target all the time.... :thinking:

 

[goninanbl00d]

A beam expander can help reduce this divergence; Laserglow markets their Hercules series of green portables for this purpose.

It's in their April newsletter, on this page:

Laserglow Technologies - Handheld Lasers, Alignment Lasers and Lab / OEM Lasers

Even then, over 30km, the beam will have diverged massive amounts, even with a beam expander. You may want to talk to the engineers at Laserglow, they may be able to come up with something for you.

Here's the links to their products:

Laserglow Technologies - Handheld Lasers, Alignment Lasers and Lab / OEM Lasers

Laserglow Technologies - Handheld Lasers, Alignment Lasers and Lab / OEM Lasers

 

[madog]

It looks to me like you are trying to send and recieve information. Like the fellow above said, even if you overcome the problems of wind and divergence, you will need a laser that can be modulated. That would require a labstyle laser.

 

[Cyparagon]

Forgive me if this is a dumb question, mister cramp, but:

Why?

 

[andreicramp]

Thank you all for taking the time to reply.

@Cyparagon ;I need to show my clients that there are no obstacles(trees buildings etc ) between the 2 antennas.

 

[anselm]

just get some binoculars instead then.

 

[Cyparagon]

Take a picture of one antenna from the top of the other. If there is a clear line of sight, then there are no obstacles. No complicated laser equipment needed.

 

[sampson]

I need to show my clients that there are no obstacles(trees buildings etc ) between the 2 antennas.

This is not practical.

 

[rvrh3]

...and at 30 meters high, the horizon is only 19.55 miles away from the tower.

 

[2100]

...and at 30 meters high, the horizon is only 19.55 miles away from the tower.

Hi,

VHF/UHF Line of Sight Calculator

Total radio horizon is 28 miles, or 46km.


To the original poster. It'd be mighty difficult to aim. I'd suggest just get on top of of 30m for both places, get one of those 5W UHF transceivers. If its really line of sight you should be able to get reception to each other. And a mobile phone as comms of course. To further confirm I think a high powered greenie or a 1.5W 445nm custom job with focusable lens at Buy Sell & trade here should work.

You can just rely on pure sight, but since you mentioned clients you may wisht to record it down on a videocam, nowadays an affordable 2nd hand D90 with a 50 or 85mm f1.8 lens would be able to see slightly better than a human eye. The green/blue flash from the laser should be enough proof.

You'd need the divergence. I have targets which ranges from 21km all the way to the visual horizon (51km away) here. It is not easy to aim with wind and tripod movement factored in. Handheld would mean there is a chance of the other side seeing flashes of the laser, better for "confirmation".

9km
YouTube - 1 watt Blue Laser at 9 Kilometres Range

The video looks very dark. A normal dSLR with cheap 50 f1.8 or 85mm f1.8 lens would make it look much brighter than the eyes can see.

YouTube - Canon 550D + Sigma 30 mm f1.4 @ Night


Hope my idea helps.

 

[Flaminpyro]

I would have to agree with Cyparagon what you need is a video camera
and take pictures of one antenna while your on top of the other one
that should prove to your client there are no trees growing 90' high in the way.
And then come back here and show us the video

Welcome to the forum :wave:

 

[Haloid95]

A 50mw-80mw laser (green) should do the trick, and welcome to the forum.

 

[rvrh3]

Hi,

VHF/UHF Line of Sight Calculator

Total radio horizon is 28 miles, or 46km.

I stand corrected. Thank you.

 

[2100]

I would have to agree with Cyparagon what you need is a video camera
and take pictures of one antenna while your on top of the other one
that should prove to your client there are no trees growing 90' high in the way.

I can see a couple of antennas of my neighbouring country (Indonesia). Even at 21-25km it is very difficult to see a big 200m tall type of steel mast (self supporting pyramid type - no guy wire). I can see the red warning lights reasonably clear at night against a black sky background.