increase wifi antenna = increase reception?

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yawnbox

Junior Member
Nov 13, 2006
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I am working on a wireless 802.11b/g project. It entails a mobile penetration kit with the use of a powered (500mw) USB adapter. Regardless, I will be adding a high-gain antenna to the adapter, but out of curiosity, if I were to use a power splitter, such as this 3-way signal splitter from HyperLinkTech, and using 3 antennas, will that increase my ability to receive external signals? If i was to use 3 omni-directional antennas, I would have them at different angles-- one horizontally mounted, one at 90 degrees, and one vertically mounted. (my targets would be below me and above me-- a commercial environment). Give me any info you got, I want to learn as much as I can about this and relating topics. Thank you.
 
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ScottMac

Moderator<br>Networking<br>Elite member
Mar 19, 2001
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It would be worse than using a single decent antenna.

Putting the three loads (antennas) in parallel, but in different signal planes, would reduce the signal in any one of those planes to 1/3 (without considering losses, which would be substantial .... on the order of 1/5th to 1/8th of the total signal).

Splitters are most-often used to cluster a group of sector antennas (antennas that cover a smaller horizontal arc, typical is 90-120 degrees).

You also need to be mindful of altitude with an omni directional antenna because the pattern is not spherical, it's mutilated donut shaped and there is a cone-shaped shadow area for some distance from the azimuth center at the top and bottom that will get larger as you move the antenna higher.

500mw is way too strong. You'll roast yourself, piss off the neighbors, and your estate will likely receive a substantial fine from whoever manages the rf spectrum in your part of the world.

Darwin is watching, be careful.

Good Luck
Scott

 
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spidey07

No Lifer
Aug 4, 2000
65,469
5
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That's way too much power, good luck if you get caught. As mentioned one single antenna will be best.
 
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yawnbox

Junior Member
Nov 13, 2006
10
0
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Originally posted by: ScottMac
It would be worse than using a single decent antenna.

Putting the three loads (antennas) in parallel, but in different signal planes, would reduce the signal in any one of those planes to 1/3 (without considering losses, which would be substantial .... on the order of 1/5th to 1/8th of the total signal).

Splitters are most-often used to cluster a group of sector antennas (antennas that cover a smaller horizontal arc, typical is 90-120 degrees).

You also need to be mindful of altitude with an omni directional antenna because the pattern is not spherical, it's mutilated donut shaped and there is a cone-shaped shadow area for some distance from the azimuth center at the top and bottom that will get larger as you move the antenna higher.

500mw is way too strong. You'll roast yourself, piss off the neighbors, and your estate will likely receive a substantial fine from whoever manages the rf spectrum in your part of the world.

Darwin is watching, be careful.

Good Luck
Scott
Click to expand...

I kinda figured that the signal would be divided up, although it didn't sound like that was the case in a scenario I read about with cantennas:

If two are good then three must be better. I do not think you get 3db for every one you add but it does improve a little. Since db is a log scale, 3 db increase would be double the power level.
Click to expand...
I actually kept increasing this to 5 cans just to see what would happen. Three seemed to be the best and after that it started to drop off. An open stub made things much worse so all inputs need to be connected. The source was a Netgear home style router connected to an antenna about 2 miles away. Here is what that looks like.
Click to expand...

I didn't think 500mw was too strong... the external USB adapter that i was reading about seemed like the best choice for effective data gathering. But if you know something I don't, I'd love to know about it.

I'm guessing that's an attempt at a "nice" name for war driving.
Click to expand...

I am a security consultant and I am also studying for my CISSP.
 
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ScottMac

Moderator<br>Networking<br>Elite member
Mar 19, 2001
5,471
2
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Yeah, right. Whatever.

3db represent a doubling of (in this case) power.

IF you had 10mw out from the AP, into a 3db antenna (ignoring things like cable and connector loss) your effective radiated power (and receive gain) would be 20mw.

So if you took that antenna and added another with a splitter, you'd get another 3db (to 40mw).

Now, to double again, you need TWO antennas (and a four-way divider). ... now you're at 80mw (again, with theoretically impossible no-loss dividers, cable, and connectors) ... and youve got a double-two antenna.

To double the power again, you'd need FOUR MORE antennas (and an eight-way divider).

and so on.

500mw into the antenna is against the law and physically dangerous to the uninformed and unsuspecting such as yourself.

Unless, of course, you were duped with "marketing math" and taken for a ride, so to speak.

Good Luck

Scott


 
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yawnbox

Junior Member
Nov 13, 2006
10
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Originally posted by: ScottMac
500mw into the antenna is against the law and physically dangerous to the uninformed and unsuspecting such as yourself.
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I would like to read more about this. Could you cite it? Thank you.

EDIT: I just read from my CWNA book that FCC permitted devices and/or complete systems are perfectly legal.

EDIT2: this is an illegal product (800mw AP)? It's been documented being used in schooling environments:
http://www.renasis.com/products.html
 
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ScottMac

Moderator<br>Networking<br>Elite member
Mar 19, 2001
5,471
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AP output to the antenna is (on commercial systems, like Cisco APs) 100mw on 2.4GHz (802.11b/g) and 40mw on 5.6GHz (802.11a).

Any additional gain comes from the antenna to a maximum permitted EIRP (which varies by country and application).

Which chart in the CWNA book are you referring to?


 
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yawnbox

Junior Member
Nov 13, 2006
10
0
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I was reading Figure 5.3, 'FCC CFR 15.204' from my CWNA third edition on page 137. I would imagine that the FCC rules are elsewhere on the net, but they're rather difficult to read. I like how the CWNA book sums it up for the reader. SO basically since I'm adding any of my own amplifiers i'm not violating any of the FCC rules, especially since the antenna that i'd be attaching isn't above 9dbi. Or so I think.
 
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xSauronx

Lifer
Jul 14, 2000
19,582
4
81
Originally posted by: yawnbox
I was reading Figure 5.3, 'FCC CFR 15.204' from my CWNA third edition on page 137. I would imagine that the FCC rules are elsewhere on the net, but they're rather difficult to read. I like how the CWNA book sums it up for the reader. SO basically since I'm adding any of my own amplifiers i'm not violating any of the FCC rules, especially since the antenna that i'd be attaching isn't above 9dbi. Or so I think.
Click to expand...

youre arguing with people who actually know what theyre talking about when it comes to wireless. youre being given helpful advice that can keep you out of legal trouble (nevermind the physical risk you seem willing to take in dealing with wireless technology youre not familiar with)

do yourself a favor and listen to what youre being told. nobody here gives bad advice for the hell of it, just to ruin some guys day or make things harder on them.

also FCC CFR 15.204

that doesnt seem *that* difficult to read

CWNA Certified Wireless Network Administrator Official Study Guide

this CLEARLY states the following:

When additional devices from other vendors, such as amplifiers, are added into the system, the manufacturer's certification no longer applies and you must obtain your own certification for your system.
Click to expand...

this information couldnt possibly be made clearer. i have to doubt whether or not your particular book is worth a damn (how many such CWNA guiders are there???) or whether or not you have a problem with reading comprehension (as i find it hard to believe such important information might not be in your book)
 
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yawnbox

Junior Member
Nov 13, 2006
10
0
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i apologize. i didn't think my statement of reasoning was an attempt to be any more knowledgeable. the first thing i did was ask for a citation, because i'm very willing to read more about these topics. and i never stated that i was adding my own amp. the wireless adapter that i posted a link for is approved by the FCC. i don't believe blanket statements without the proper documentation. your opinion is no better than a wikipedia article. i've yet to read anywhere how 500mw of electromagnetic radio waves is damaging. what does a microwave put out to cooks my food?

oh. my previous post should have included the word not...

...I'm [not] adding...
 
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