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Eliminateur
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Best way to pass through trees?

Fri Jun 29, 2007 9:03 pm

Hi,
i have to link 2 sites that are ~ 1KM away(city, suburb).
one site has a 30mt tower, that's no problem, the other site is a 2-story house roof on which a tower isn't allowed, so it will have a 3mt mast(2mt from the tallest point), the tallest point in the house must be 10mts~

the problem: a treeline(actually more than 1) between both sites composed of HUGE trees, more than 40mts in height(tower is totally blocked by the trees even from the roof).

worse is that the antennae ont he tower site isn't pointed directly at the house(but it's on the cone of the dish).

we did preliminary test yesterday with a yagi and a small dish(i think 14/16dBi) with a 1.5mts pole and we did manage to get the remote signal, but the RSSI was -93 and signal quality was below 4%, and it would drop almost instanly(well the pole wasn't exactly firm).
The weird part is that we got signal when the dish was pointed to the ground!.

any ideas/sugerences on dish sizes/gains/frequencies?

we used a RB52 tik' on the tower @ 2.4GHz
Last edited by Eliminateur on Sat Jun 30, 2007 1:05 am, edited 1 time in total.
 
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warwick09
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Re: Best way to pass through trees?

Fri Jun 29, 2007 11:46 pm

Well in any event youd like to use a lower frequency if you plan on punching through trees as the leaves/moisture would pretty much tear anything above 2ghz apart. With that being said I would look into using 900Mhz with all aerials being horizontally polarized for maximixed rejection/isolation.

With 900Mhz youd expect to gain a 10+dbm increase in received power over 2.4Ghz and about 20dbm for 5.8ghz... Not exactly approximates but are near enough.

Also you can look at the channel spacing which would give you an increase in range. with 5mhz spacing offering a 3dbm increase in received power.

I have a few 3 mile 900mhz links with absolutely no line of sight and get -61 (15dbi grid) with the base being a 13dbi sector. all vert polarized.

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Eliminateur
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Re: Best way to pass through trees?

Sat Jun 30, 2007 1:01 am

i thought about that, but 900MHz is licensed here and getting a licence(not to mention getting new antennaes) would be more troublesome and expensive than running a fiber-optic cable undrground between the sites.
 
HellMind
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Re: Best way to pass through trees?

Sat Jun 30, 2007 1:16 am

The lower is the frequency the cheaper is the cost of the antennas.
I think it wold be cheaper.
I would like to try 900mhz if everything goes right getting a license won't be much trouble.
 
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stephenpatrick
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Re: Best way to pass through trees?

Sat Jun 30, 2007 1:50 am

Chainsaw . Bzzzzzzzzzz .
Problem solved :-)

Seriously, only low-freq signals <1GHz go through trees
Above that, major problem, no "hi tech" solution

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Eliminateur
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Re: Best way to pass through trees?

Sat Jun 30, 2007 3:35 am

which minipci boards support 900MHz?
 
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jwcn
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Re: Best way to pass through trees?

Sat Jun 30, 2007 4:18 am

Rb133 is your best option. Just make sure whatever you do to leave tx power set to default. Everyone I've changed even running as low as 13dbm have fried the SR9 within a few days.
 
Eliminateur
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Re: Best way to pass through trees?

Sat Jun 30, 2007 4:23 am

i meant on the minipci boards, not the host board :)

so either if i lower or raise tx power, i'll fry it?

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