Line of sight communication

who knows the steps in constructing Line of Sight Communictaion between two locations... please help. thanks!

It depends of the range.

For close range you can use IR LEDs to do it and an 40Khz IR reciver IC.But that dosent give much bandwidth.There are some IR transiver ICs that can do up to 100 Kbit/s but those dont have much range.

For long rage you beter use an laser but it must be exsactly lined up.

FM radio is line of sight. Semaphore is line of sight.

Mike

FM radio can go trugh an wall and light cant.So radio is not line of sight.

You might want to be more clear on what you might communicate. Along with what's already been stated, a flashlight or lantern, waving of arms, etc. No intent to be funny here. Just making you think a little.

Microwaves are popular and I'd guess that bandwidth is considerable. I know of several hobbyists who are experimenting with lasers bounced off of clouds or tall buildings. They send data at a relatively slow rate and depend on signal processing to separate the intelligence from the random noise that goes along with this method.

Amateur radio publications might be one source of info.

First of all, lets clarify. "Line of sight" simply means you have a direct "free space" path between transmitter and receiver antenna. However, if your receivers are moving that may not always be the case.

Now its true there are different kinds of modulation schemes that work better depending your line of sight (and more importantly your SNR). So if you know for a fact that you'll have line of sight at all times, look for a transmitter/receiver pair that does some type of digital modulation. Frankly, analog modulation (AM, FM, PM) schemes suck, they have terrible bandwidth requirements and transmitter draw backs. But they are easy to do, which is the appeal. Especially AM, it is super easy to demodulate since it is a coherent modulation scheme (no synchronization required), but thats not the case for FM and PM. Now if you actually look at FM, you'll notice one interesting characteristic about it, it requires infinite bandwidth, (which is the reason for the 200Khz guard bands on your FM radio). But there is a rule (called Carson's Rule) given a few variables you can calculate your 99% bandwidth requirement.

The main draw back of digital modulation schemes is the obvious need for a ADC and DAC, but their SNR requirements, BER, and Bandwidth efficiencies more than make up for a few extra parts.

I recommened either a M-ary PSK modulation, a QAM modulation, or an FSK modulation, either will suit an line of sight application well. You will also be able to get much higher data rates with a digital scheme. For the most part the only type of modulation that is really still done in analog land is the radio. Surely you have an RF front end, but thats only for the up conversion, that doesn't do the modulation.

Good luck!

Someome Electro wrote:

FM radio can go trugh an wall and light cant.So radio is not line of sight

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I hate to correct you, but this isn't true. An LOS transmission is one that is directional, as opposed to omnidirectional, and requires the transmitter to be pointed at the reciever. An LOS transmissions only limitation is the curvature of the earth, and major terrain features like large hills, thick forestry or mountains. In the Army, I operated a Line of Sight radio transmission systems node with three antennae on 15 meter masts. We lined our antenna up with azimuth and back-azimuth coordinates, and linked FM radio communication via LOS. We operated in UHF and SHF bands and sometimes had obstructions like trees and buildings in the way, but they were not enough of a hinderence to prevent the signal from transmitting through. Admittedly, the signal might not be as strong, but it was still adequate, and it WAS FM radio.

I know radio cant go trugh hills and water.

That is a headace wen driving in a landscape sourunded by hills.The radio cant pick up anything.There is also not good reception in a realy deep celler but some stuff still comes trugh.

But radio can penetrate an wall whith no problem at all.Wen light can be stoped by a les than 0,1mm thicck of an non transparent material.

This is all true, but, I just wanted to dispell any confusion as to what line of sight really means. A LOS transmission can be radio, laser, IR, visible light, etc. Radio CAN be used for LOS communication too, all that is required is 2 DIRECTIONAL antenna (dish style) with 2-way radios, antennae pointed directly at each other, seperated by no more distance than the strength of the radio amplifer and curvature of the earth limit.

Someone Electro said:

Radio cannot go through hills and water.

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A popular misconception that still manages to corrupt young minds.

For most practical purposes LOS transmission just doesn't work. Most cases need omnidirectional antennas because they're moving, or the location of the receiver is unknown to the transmitter.

I suppose you could do some sort of "searching" for the receiver, or have the receiver send a signal back and try to estimate the channel (range and location). But as you'll see there are some information theoretic results that show feedback (receiver -> transmitter) will not help you.

heathtech said:

This is all true, but, I just wanted to dispell any confusion as to what line of sight really means. A LOS transmission can be radio, laser, IR, visible light, etc. Radio CAN be used for LOS communication too, all that is required is 2 DIRECTIONAL antenna (dish style) with 2-way radios, antennae pointed directly at each other, seperated by no more distance than the strength of the radio amplifer and curvature of the earth limit.

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I would disagree with your suggestion!, but only on ONE point.

LOS doesn't have to be directional, two VHF (or higher) radio transceivers using quarterwave whips (which are omnidirectional) are 'line of sight' - there's no need for directional aerials.

If you both stand on top of hills, and can see each other, then the radio link works - if one goes down the far side of the hill then LOS is lost, and the link no longer works. In 'flat' country the limiting factor is obviously the curvature of the earth.

As already suggested, LOS isn't just an optical path, it's anything which works - and radio will work through some obstructions (houses etc.), although it generally weakens the signal.

Interestingly enough, some lower frequencies (the lower VHF ones) will actually 'bend' and work slightly further than theory would predict, by the time you reach UHF this effect is pretty well lost, and microwaves are almost optical in their LOS characteristics.

LOS is simply a way of describing the path (or channel) between transmitter and receiver antennas.


If you have LOS, there is nothing blocking your path. If you don't, you've perhaps got a building, trees, dog, etc.. in your path.

Nigel wrote:

LOS doesn't have to be directional, two VHF (or higher) radio transceivers using quarterwave whips (which are omnidirectional) are 'line of sight' - there's no need for directional aerials.

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Yes, this is true, but this really defeats the purpose of LOS. We are getting into semantics here, but the advantage of a directional antenna is signal strength. Using the same transmitter power, an LOS directional broadcast is superior to omnidirectional if transmitting to a stationary reciever. I know most of you already know these things, but I think it is just good to post for the advantage of people who aren't aware of it. (Lest we forget the original poster who might be a student) Another aspect of LOS transmission (directional) is it is more difficult to intercept without knowledge of the antenna coordinates. Maybe the advantages in communication are mostly military, but they ARE there.

_3iMaJ wrote:

For most practical purposes LOS transmission just doesn't work

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Again, I refer to the reasons above that there are practical advantages to LOS, just not , as you say, for moving recievers.

_3iMaJ wrote:

For most practical purposes LOS transmission just doesn't work

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Again, I refer to the reasons above that there are practical advantages to LOS, just not , as you say, for moving recievers.[/quote]


I didn't say that LOS wasn't practical. If you can get LOS you should absolutely take advantage of it for reasons of the wonderful SNR, HOWEVER, I did state that in most practical situations LOS just isn't possible.

IE cell phones, radio communcations, sonar, radar, the list goes on and on. There are far more non-LOS communications than LOS (speaking strictly in terms of wireless communications).