How strict is line of sight?

Question

The college where I work is wanting to expand our network connection out to the field house building, located about 1/2 to 3/4 mile away from the rest of campus. I'm looking at one of these as a possible solution:

http://www.streakwave.com/Itemdesc.asp?ic=Q-Bridge&eq=&Tp=

I've used them before and been very happy with the results - I just have to keep in mind the throughput limitations (I couldn't run a whole dorm off one of these, for example). But my question here is on the line of sight requirement. In previous uses, line of sight has been perfect. In this case, it's a little less so. There are no buildings in the way, but due to a few trees I can't get a direct view of one building from the other. However, given that I'm only going <1/4 of the rated distance of the connection, is the signal likely to have enough power to establish a good connection?

I think this is a question for www.streakwave.com – lg. Jul 13 '10 at 14:15 — lg., Jul 13 '10 at 14:15

score 3 · Answer 1 · answered Jul 13 '10 at 14:32

There are equations for figuring out this kind of thing. The tricky thing to find is exactly how opaque whatever kind of leaves those trees have are to 2.4000-2.497GHz radio waves, and how thick they are. The spec-sheet includes the antenna data as well as the transmission power, which are the other things you'll need. Once you have all that, you can figure out expected signal loss over that path.

I am not an RF Engineer, so I don't know those equations. The people who run those FreeNets you find in some cities have spent a lot of time on this kind of question are the kinds of people who'd know this stuff. And, you know, RF Engineers.

My crystal ball says it'll probably work, so long as you get your pointing exactly right. Trying is probably your best bet. If that fails, time to go for the grounded masts to get around/over the trees.

score 2 · Answer 2 · answered Jul 13 '10 at 14:16

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There are arguments both ways but ultimately there's literally no way of knowing for sure but to try it out. Of course there's going to be a huge difference between summer and winter but worst comes to worst you could always have a small 'accident' with a chainsaw :)(

answered Jul 13 '10 at 14:16

Chopper3

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I'd add towers to make it line of sight. Also remember grounding. Few things make the day more exciting than a lightning strike. – Bart Silverstrim Jul 13 '10 at 14:19
If they're evergreens the signal may be worse in winter with a snow load. If they're deciduous then possibly better due to lack of leaves, but snow will still be a factor. – Dennis Williamson Jul 13 '10 at 14:46
High power laser... – Bart Silverstrim Jul 13 '10 at 14:52
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'Apocalypse Now'-style tree-line napalming, Doors soundtrack optional. – Chopper3 Jul 13 '10 at 16:00
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Also remember trees have a habit of growing, it may work within tolerance now, but next year....or when the wind blows....or when that horde of locusts lands in the tree.. – SqlACID Jul 13 '10 at 16:45
Agent Orange then? – Chopper3 Jul 13 '10 at 16:46

score 2 · Answer 3 · answered Jul 13 '10 at 14:27

I don't think that some trees will cause total lost of connection {I don't know what will happen in the "forest" case :} }

Is there a minimum throughput that you want to achieve ? If not, you could either increase the transmission power {to legal bounds} , decrease the transmission rate by hand in order to have a more "robust" connection.

In any case, i don't think that with your equipment you 'll have problems :>

How strict is line of sight?

3 Answers3