Wifi between two houses under 1km, line of site from roof...

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greminn

181 posts

Master Geek

#25970 8-Sep-2008 11:14

Hi There,

I have a friend in Te Arhoa who would like to get access to her dads wifi (with his permission). She lives under 1km away and we think that we have LOS from the roof of both places. She hasnt got a phone line on at home and therefore no DSL (until naked DSL comes to Te Arhoa! ha).

We havnt got any huge budgets to speak of... so as cheap as possible.

Would be great to have the link wifi'ed in her house.

At the very begining here, so where do we start?

Simon

Madmax77

152 posts

Master Geek

#163031 8-Sep-2008 11:21

1km is quite a long way out and would require a lot more power than your average 802.11b/g/n transmitter normally puts out, the easiest way to do it would be to set repeaters up every 50-100 metres and link them that way, however not very practical in your case. Perhaps there is some type of directional transmitter which may work but I fear this will cost quite a bit.

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greminn

181 posts

Master Geek

#163035 8-Sep-2008 11:34

Madmax77: 1km is quite a long way out and would require a lot more power than your average 802.11b/g/n transmitter normally puts out, the easiest way to do it would be to set repeaters up every 50-100 metres and link them that way, however not very practical in your case. Perhaps there is some type of directional transmitter which may work but I fear this will cost quite a bit.

Yea - i was looking at something like this:

http://www.gowifi.co.nz/products/combo-wifi-kits/14dbi-point-to-point-kit.html

I think we can get away with $200-300 if need be...

Simon

nutbugs

269 posts

Ultimate Geek

Lifetime subscriber

#163037 8-Sep-2008 11:38

this looks like fun - and cheap :)

http://www.usbwifi.orconhosting.net.nz/

coffeebaron

6211 posts

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#163038 8-Sep-2008 11:42

greminn: She hasnt got a phone line on at home and therefore no DSL (until naked DSL comes to Te Arhoa! ha

Naked DSL is available anywhere that you can get DSL. The only catch here is this maybe considered a rural area, so would be at a higher price.
You can get special outdoor, long range wifi gear for LOS setup, but my guess is start at $1000 and move up from their - so not cheap.

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iainw

75 posts

Master Geek

#163044 8-Sep-2008 12:09

Facts and figures for a 1km bridge link.

Using 2.4GHz (802.11b/g) you need a minimum of a 15dBi antenna at either end, and a 15dBm radio. Bear in mind that to opperate legally in NZ, your total EIRP (energy transmitted from the antenna) at 2.4GHz cannot excede 30dBm. You also require a minimum of 3.4m clearence throughout the entire link. ie if you used a laser pointer to determain LOS, your RF-LOS actually requires you to be able to draw an imaginary tunnel, 3.4m around the laser beam and the entire tunnel is clear.

If you use 5.8GHz (802.11a), you still need a minimum of a 15dBi antenna at either end, and a 20dBm radio (5.8GHz has greater Free Space Path Loss (FSPL) than 2.4GHz. The advantage of 5.8GHz is that your maximum EIRP is now 53dBM in NZ, however your maximum IR (radio + any amps) is 20dBm.

If you want wifi inside your client house as well, you need a dual radio unit (802.11a/b/g).

Setting this up using best of breed equipment would set you back somewhere around $2.5 - 3k. Using mid market equipment would let you drop this price significantly.

Questions to ask yourself
- how important is the connection? Is it acceptable if it requires resetting occasionally, or doesnt always work when it is raining?
- what sort of traffic is going over it? Is it just for internet access or are you planning on running VOIP over it?
- Do you actually have RF LOS?

Barring the RF LOS, a bridge link can successfully be set up for up to 14km using 802.11a equipment, it is entirely a question of how much is it worth to you.

If you are able to provide GPS co-ordinates for the two buildings, I can generate a profile for you which will tell you what sort of clearance/mounting height etc is required given the terrain.

iainw

75 posts

Master Geek

#169488 7-Oct-2008 09:36

The thing you need to bear in mind with wireless bridge links, is that RF line of sight is completely different to visual line of site.

Visual line of sight is like a laser beam, either you can see something directly, or you can't.

RF line of sight relies on a Fresnel Zone. This zone is a 3D tunnel of airspace around your laser line of site. In reality it is parabolic, and the diameter is greatest at the halfway point, but for planning purposes easiest to assume it is a tunnel.

This is dependant on only two things - frequency and distance. Antenna gain and transmit power are irrelevant. At 300m, you will need roughly 1.8m if using 2.4GHz, and 1.2m if using 5.8GHz. This is the diameter of your invisible tunnel around an imaginary laser beam. If anything interupts this space, your bridge link will start to suffer dramatically.

You can purchase equipment designed specifically for near LOS (nLOS), or non line of site (NLOS), however you are talking thousands of dollars for this solution.

Unfortunately for the NZ psyche - wireless does not lend itself well to No. 8 wire and duct tape solutions.

sbiddle

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#169490 7-Oct-2008 09:49

I think you're probably looking at somewhere arund the $1k mark for a good setup to deliver this.

A couple of Miktotek RouterOS boxes with WiFi kits and two good aerials would do this for you and work well. You are not going to find a solution much cheaper than this that will deliver any form of performance.