Antenna Polorization

[Joedetic]

I've got a wifi bridge that is connecting an outbuilding to a main building where the network is housed. What I've got is the WiFi AP in the main building and the bridge in the outbuilding and the signal was dropping out due to low strength so i've bought a YAGI antenna (directional waveguide antenna / cantenna whatever you are most comfortable calling them).

 

The idea is that i fit this onto the bridge and aim it at the AP. Here comes the thing i'm not sure about. Is the idea that you have the antenna's on different polorizations to each other or the same?

 

So if the small rubber duck antenna on the AP is aligned vertically to the earth (aka perpendicular) is it in vertical polarization?

 

Are there any radio hams or wireless experts reading that can help? lol

 

Cheers

[SimpleSi]

Yep - if the rubber duck's vertical - its vertically polarised - so align the yagi elements vertically as well

 

(Assuming your other antenna is an actual yagi)

 

regards

 

Simon

[Joedetic]

So both vertical or both horizontal. OK

 

Cheers!

[Geoff]

so i've bought a YAGI antenna (directional waveguide antenna / cantenna whatever you are most comfortable calling them).

 

These are illegal to use on unlicensed bands (such as WiFi). For two reasons:

 

1) Specifically you are not allowed to use directional antennas.

2) The combination of the stock radio amplifier plus the directional antenna will likely put you over the 4mw maximum signal strength requirement.

[Joedetic]

Hmmmmm. Crud.

 

I dont actually have an amplifier and wouldnt even consider hooking one to it cause that would be just asking for trouble. But no directional antennas. That's a bit naff.

 

Maybe i could get the amplifier and hook it up to point it at the parrot to see if that shuts the bloody thing up.

 

Quick question though. If directional waveguide antenna's are illegal then why do CISCO sell them and why are there two mounted in one of the CCNA labs at my university?

[john]

Are you sure its a Yagi and not another clone that is legal?

[Geoff]

I dont actually have an amplifier and wouldnt even consider hooking one to it cause that would be just asking for trouble.

 

You misunderstand radio engineering (unsurprising). The total output of a transmitter is a function of it's amplifier (the electronics in the box) plus the antenna. If you alter the antenna in any way, you alter the output power of the device.

 

If directional waveguide antenna's are illegal then why do CISCO sell them and why are there two mounted in one of the CCNA labs at my university?

 

The obvious answer is they applied and got a license that exempts them. Unsurprising really if they throwed enough money at the problem.

[Joedetic]

The Cisco instructor said they were Yagis but maybe she was mistaken.

 

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ih=002&sspagename=STRK%3AMEWN%3AIT&viewitem=&item=120136361081&rd=1&rd=1

 

That's what i've bought. I'm thinking possibly not a good idea now

[john]

The Cisco instructor said they were Yagis but maybe she was mistaken.

 

http//cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ih=002&sspagename=STRK%3AMEWN%3AIT&viewitem=&item=120136361081&rd=1&rd=1

 

That's what i've bought. I'm thinking possibly not a good idea now (

Hmmm, I have about 4 of them, or at least items that look identical to them, Buffalo sold them with routers ages ago, we've used them internally in temp setups and a P2P link between a portercabin and the main building

[Geoff]

No, those are not YAGI's. YAGI's look like TV antennas.

 

http://en.wikipedia.org/wiki/Yagi_antenna

 

However, they are still illegal. As they are directional. To be specifc, they are wave guide antennas.

 

http://en.wikipedia.org/wiki/Waveguide_%28electromagnetism%29

[john]

If they are illegal why are they so freely avalable at e-tailers such as Dabs, PC World have even sold ones that look like them off eBay that Joedetic is linking to? Surely if they needed licencing they would be more restricted sale or something? Literally I got 4 free with 4 wifi points I got ages ago and they never said anything on any of the literature that said you need a licence or anything like that :s

[Joedetic]

Right...there seems to be a lot of confusion on the internet as to what is referred to as a YAGI. I personally had thought that a YAGI was an antenna with driven elements, reflection elements and another one i forget. As you put it "like TV antennas."

 

If directional antenna's are illegal then how come you can get them at maplins under the wifi section?

 

I have a feeling that it's only illegal if the output is over a certain wattage...i'm not sure on that one though, as Geoff has said i misunderstand radio engineering. I fail to see why it's unsurprising. I might have been really good at it *rolls eyes and dreams* lol

[localzuk]

We have directional antennae installed in 3 places in our school, neither are 'licensed' I believe - and both run on normal wifi frequencies, and these were installed by out county council and by one of our suppliers - neither of which would be breaking the law akaik.

 

Geoff, could you please provide a source stating that they are illegal without a license?

 

(Note: None of these use the 5Ghz bands, all are making use of 2.4Ghz (b and g)

[webman]

Ofcom says that for the unlicensed 2.4GHz band that the EIRP must not exceed 100mW.

 

Also some more information here.

[Gerry]

I've been doing a little research into connecting 2 buildings via Wi-Fi. It's illegal to use Band C of the 5GHz range without a licence from Ofcom, and using Band A and B for a different purpose than they've been assigned (i.e. Band A is for indoor use only, and Band B is for mobile networks).

 

http://www.solwise.co.uk/wireless-5.htm

http://www.ofcom.org.uk/radiocomms/ifi/licensing/classes/rlans/5.8_fwa_index/

[Joedetic]

OK. So from what I can gather. Directional antenna's ARE legal (because i cant find anything that says they arent) but power on all antennae using the 2.4GHz frequency is limited to 100mW.

 

So what i need to find out is the gain of all the components before i can go on the web and try to find the calculations that tell me whether it's legal to use this thing i've now got sat on my bedroom floor lol. It says it's a 20dBi antenna. But whether that's before or after cable and SMA connector losses i dont know.

[Gerry]

Try this link:

http://www.solwise.co.uk/los.htm

[Joedetic]

Hmm everything is measured in dBm on a lot of sites and i dont have that information about my antenna. I've just been told from a website it's 20dBi.

 

e.g. in the UK legal EIRP @ 2.4GHz is 20dBi,

 

More research first though.

[Gerry]

Have a look at page 6:

http://www.ofcom.org.uk/radiocomms/ifi/tech/interface_req/uk_interface_2007.pdf

 

And try this site:

http://www.wifinerd.com/wifi-calculators.html

[Joedetic]

BTW, i'm only working to 2.4GHz not 5GHz and have no plans to switch at the moment.

 

Again, that is assuming i know what the cable loss is (including the SMA connector) which i dont.

[Gerry]

On the http://www.solwise.co.uk/los.htm site there's an example for a 2.4GHz setup and it assumes a standard device is to be used and states 100mW and 20dBm.

 

Perhaps you can figure out the cable and connector loss from here:

http://www.solwise.co.uk/wireless-cable.htm