Wi-fi Antennae Rules For Los

[JJDinsay]

A guy from D Link has told me dat LOS only allows Wi Fi antennaes up to 6db! I thought it was 18db? Any clarification on this? Who makes these rules up here? What is der version of da FCC

[monty]

They supposedly follow European legislation (ETSI) concerning Wifi over here...

In short this means only channels 1 to 11 are available and the Effective Isotropoic Radiated Power(EIRP) can't be more then 20dBm (100mW).

What antenna you can use is easy to calculate. You just add antenna gain and deduct all losses(cable, connectors,...) from the power your accespoint transmits.

Example: Lynksys Wap11 transmits at maximum 17dBm.

I deduct 0.5dBm loss on the connector and 1.3 dBm for 1 meter of LMR 100A cable. At my antenna i get 17-0.5-1.3=15.2dBm

This means the maximum gain of my antenna would be 4.8 dBm to stay within the 20dBm limit...

On a lot of accesspoints you can reduce transmitted power, so you can hook up a high gain directional antenna while staying legal...Remember the antenna gain helps both transmission and reception, so even though you're not transmitting at high power you still have the benefit of better reception!

Now this being Thailand, I already saw 200mW (23dBm) Wifi amplifiers for sale in Bkk! Hook up a 24dBm parabolic and you're major illegal

High gain antenna's for sale from the wonderfull people at www.bangkokwireless.net

[monty]

Just got it confirmed that Thailand deregulated Wifi for indoor use only with a limit on radiated power of 100mW... Free to experiment with whatever you like as long as you stay within limits...

[sillyfools]

Just got it confirmed that Thailand deregulated Wifi for indoor use only with a limit on radiated power of 100mW... Free to experiment with whatever you like as long as you stay within limits...

Does that mean that you can point a high gain yaghi inside your house just behind the window, pointing to another location, after all whatever has a roof on top is inside, right ?

[monty]

Guess so,

only you'll have to reduce your transmitting power on your AP a lot to stay inside the 20dBm limit with a high gain yagi!!!!

[normanB]

anyone ,,,,

my rooftop is 6-7 miles line of sight to Cha-Am where i understand there's now DSL service. could a WiFi connection be set up if i can find a willing party in Cha-Am?

Springfield Condo's also line of sight about 1/2 mile with an access point, not sure yet but i think they're expensive. where's Springfield getting their connection from do you think? satellite?

would someone please lay out what's needed for a wireless connection from a DSL point. thanks.

Edited April 18, 2005 by normanB

[Firefoxx]

6-7 miles is out of range for wifi... even 1 mile is out of range, even with a parabolic antenna. Other common wireless techs also don't reach that far, at most around 1-2km. You'd need the upcoming winmax for that kind of distance. Microwave might make it, but it's prohibitively expensive and dependent on the weather.

[autonomous_unit]

6-7 miles is out of range for wifi... even 1 mile is out of range, even with a parabolic antenna.  Other common wireless techs also don't reach that far, at most around 1-2km.  You'd need the upcoming winmax for that kind of distance.  Microwave might make it, but it's prohibitively expensive and dependent on the weather.

<{POST_SNAPBACK}>

I assume you mean while staying within the proper unlicensed band signal strength?

Many people in the US use 802.11b with directional antennea to go several miles line of sight. It's a regular cottage industry of not quite legal "medium haul" wireless. They basically operate SOHO hardware at signal levels meant for an omni-directional antenna and instead put them out a high-gain yagi. I've read about nearly 20 mile links in open country areas with low background noise. The question is when someone will notice interference on the main link path or one of the lobes...

[monty]

Firefoxx, I have a 5 mile wireless link up and running using regular of the shelf available equipment in Thailand The important thing here is "Line of Sight" since the 2.4 Ghz frequencies can hardly penetrate anything else then air... Thats why you're lucky(very!) to get more then 100 Feet range indoors...

On following page you can see how it is possible to get a 5 km link while staying within the legal limits in the UK (wich are the same as in Thailand) A bit technical though...

http://wireless.gumph.org/articles/longrangelink.html

Unfortunatly, 7 miles will be out of the question doing it legal...

I will explain how it is possible, but please note that doing this in Thailand is illegal

Using high gain antennas increases the radiated power(EIRP) way above what is allowed in Thailand!!!!!

A 6 - 7 miles wireless link would be possible if your rooftop is high enough, the antenna at the other side is high enough and the fresnel zone is not obstructed...

Easy to understand if you take a look at following page:

http://www.verilan.com/wirelessnetworking/...snel-zone.shtml

If you do the small calculation you'll see that you'll need at least 37 feet clear view under the line of sight (wireless bridges work at 2.4Ghz). A 20% obstruction would give just a little loss so thats still

30 feet.

If you have this open view to a place where dsl is available then it is pretty easy to get such a link up and running.

At the dsl side you'll need an adsl router, which will plug directly into a wireless bridge connected to a high gain directional antenna.

At the other side the signal will be picked up by another high gain directional antenna, feeds it into a second wireless bridge, into which you then connect your pc.

A d-link dwl-2000ap will work perfectly as a wireless bridge, and has the neccesary connector to hook up an external antenna. Costs around 4000 Baht in Thailand...

Antenna's together with the correct connectrs/patch cables available from

http://www.bangkokwireless.net

They will mail to your home, or even have their technicians come over to set-up the whole stuff(they certainly don't worry much of the legal side, and they are Thai )

One very important thing to consider that these wirelss bridges and their calculations are a bit of black magic . Links which should work perfectly in theory simply won't work and vice versa...

It would be wise to pay the proffesionals a fee to do the necesary tests before committing. The Bangkok wireless people certainly know their stuf and seem to have some sort of boyish pleasure in doing these "slightly" illegal things...

Edited April 19, 2005 by monty