# Transmission of laser between towers?

1. Feb 2, 2013

### Gliese123

Hello there!
I was brainstorming a lot when I took a walk today. Not that I posses any type of degree in communication, although I find it interesting of IT communication and they techniques we use for cellar communication. NOW to what I thought about. Lets have an example:
If I were to transmit a huge amount of data from my current place Sweden to lets say... The UK? And nothing as sophisticated as high speed internet were available. What would be the most efficient structure of infrastructure to do so?

Then I thought about laser or concentrated electromagnetic radiation. What if there were regular mobile towers which didn't use the regular mobile communication (I mean the widespread wave length) but which were capable of fixing a some sort of laser together to form a mutual beam of some sort to the location? Would this "technique" me much cheaper since we save money on materialistic costs such as fiber optics?
Please don't call me stupid. I just want to hear what you guys have to say :tongue:

2. Feb 2, 2013

3. Feb 2, 2013

### Staff: Mentor

For distances of more than 50km, the direct line of sight can get problematic. And you can get all sorts of nasty effects from the atmosphere.
That is fast for satellites, but glass fibres are in the Tbps-range. Per fibre. You would need thousands of independent laser systems to replace a single strand of glass fibres.

4. Feb 2, 2013

### Gliese123

Yeah. There are a lot of atmospheric disturbance... But more than 50 km? Is the horizon making it problematic?

5. Feb 2, 2013

### Staff: Mentor

Right. With the visible distance d in km and the height h in meters,
$d\approx 3.57 \sqrt{h}$
For 25km (for both towers each), you need a height of 49m. That is possible. If you want to double the distance, however, tower height has to increase by a factor of four. A tower of 200m is still possible, but it is not something you can build in your backyard. Another factor of 2 (for a transmission over 200km) would need towers nearly as high as the Burj Khalifa, the tallest building in the world.

I neglected atmospheric effects here - they tend to help, so you get more distance with the same height. But at the same time, those atmospheric effects degrade the signal quality...

6. Feb 2, 2013

### Gliese123

That is really cool, interesting and helpful! Thanks alot!
Maybe several smaller towers could make it. :) But it would be rather strange. I guess the satellite version from the link is better

7. Feb 2, 2013

### Mordred

Look into mixowave links. Their are models capable of 50 km. Provided you have the height for clear line of sight. Different communication protocols are supported.