proper use of what antenna? and range Q?

HoneyPot · 01-04-2003

apologies in advanced if this is repetitive... but what about range?

So am I understanding things correctly???? I've been reading to learn, but then you read about different setups and their opinions.
Don't want to start a debate but:

GENERALLY SPEAKING

a omni 5 db would be ideal for driving / locating ?

and a 15 dBi Directional Enclosed Yagi Antenna would be more ideal for detecting an already known AP ?

If I had an ORiNOCO Wireless PC Gold Card, and used the 15dbi (above antenna) how close physically would I have to be to my AP? For example...In my house without external equipment I'll get at best 30feet with 80 % signal strength. by 50 feet with a couple of walls I'm down to 20% strength (all linksys setup though, I know linksys cards wont work with netstumbler etc.)

Would it be ridiculous to say that some dude would have to bring their Hummer up onto my front lawn to detect a decent signal strenght for my AP or can they sit accross the street? or Down the street? What?

What's realistic here?
thanks for your help

Thorn your pics are very helpfull.

HoneyPot

db8tr · 01-04-2003

Quote:

Originally posted by HoneyPot

a omni 5 db would be ideal for driving / locating ?

Many people find this a good compromise between size and sensitivity. The omni-directional nature means that no matter which direction from the vehicle the AP is located, it can be found.

Quote:

and a 15 dBi Directional Enclosed Yagi Antenna would be more ideal for detecting an already known AP ?

For connecting to a known AP (that you own or have permission to be using) a yagi will give you a stronger signal strength. It is a directional antenna, so it has to be physically pointed at the AP.

Quote:

Would it be ridiculous to say that some dude would have to bring their Hummer up onto my front lawn to detect a decent signal strenght for my AP or can they sit accross the street? or Down the street? What?

Well for an example, I can detect my AP in the basement of my house about 300 feet away from my house. Of course this is with kismet since broadcast replys are disabled and WEP and mac filtering are enabled. I have used my AP parked across the street from my house... so it is safe to assume that someone would not have to drive onto your lawn to mooch a conection. Of course, with a properly secured AP I don't worry about something like that happening.

Thorn · 01-04-2003

"Generally speaking" a 5 dB and a 15dB are good antennae for the two stated purposes.

You can predict how well a signal will be received if you know the 1) transmitted power level, 2) the receiver sensitivity, and 3) the gain of both transmitting and receiving antennae. This assumes that there is open space between both antennae. However, there are so many things that can influence the signal, it is literally impossible to predict the what the range of an anternna will be under all circumstances. Especially since you don't know the transmitted power and the gain of the transmitting antenna.

Remember too, that 2.4GHz RF gets blocked and reduced by any number of things in the environment; brick, sheetrock, steel, and trees (especially pine trees) are a few. Those things will have as much, if not more, effect on your results as the antenna.

It also depends on exactly what you are doing. When I'm in the field, I keep four (4) antennae with me. Depending on the job and even the specific task, I may be using a 3dB omni, a 4.5 dB omni, a 8dB yagi, or a 19dB panel.

Finally, don't get to hung up on the gain numbers as an absolute, because gain expressed as a deciBel is by definition, relative to a known power source.

Thanks, I'm glad you found the diagrams useful.

01-04-2003	#1 (permalink)
HoneyPot Registered Member Join Date: Dec 2002 Location: Ask your spouse Posts: 26	proper use of what antenna? and range Q? apologies in advanced if this is repetitive... but what about range? So am I understanding things correctly???? I've been reading to learn, but then you read about different setups and their opinions. Don't want to start a debate but: GENERALLY SPEAKING a omni 5 db would be ideal for driving / locating ? and a 15 dBi Directional Enclosed Yagi Antenna would be more ideal for detecting an already known AP ? If I had an ORiNOCO Wireless PC Gold Card, and used the 15dbi (above antenna) how close physically would I have to be to my AP? For example...In my house without external equipment I'll get at best 30feet with 80 % signal strength. by 50 feet with a couple of walls I'm down to 20% strength (all linksys setup though, I know linksys cards wont work with netstumbler etc.) Would it be ridiculous to say that some dude would have to bring their Hummer up onto my front lawn to detect a decent signal strenght for my AP or can they sit accross the street? or Down the street? What? What's realistic here? thanks for your help Thorn your pics are very helpfull. HoneyPot __________________ I am a bomb technician, if you see me running...try to catch up!!! Last edited by HoneyPot : 01-04-2003 at 04:19 PM.

01-04-2003	#3 (permalink)
Thorn Did you do the math? Join Date: Apr 2002 Location: Villa Straylight Posts: 10,096	"Generally speaking" a 5 dB and a 15dB are good antennae for the two stated purposes. You can predict how well a signal will be received if you know the 1) transmitted power level, 2) the receiver sensitivity, and 3) the gain of both transmitting and receiving antennae. This assumes that there is open space between both antennae. However, there are so many things that can influence the signal, it is literally impossible to predict the what the range of an anternna will be under all circumstances. Especially since you don't know the transmitted power and the gain of the transmitting antenna. Remember too, that 2.4GHz RF gets blocked and reduced by any number of things in the environment; brick, sheetrock, steel, and trees (especially pine trees) are a few. Those things will have as much, if not more, effect on your results as the antenna. It also depends on exactly what you are doing. When I'm in the field, I keep four (4) antennae with me. Depending on the job and even the specific task, I may be using a 3dB omni, a 4.5 dB omni, a 8dB yagi, or a 19dB panel. Finally, don't get to hung up on the gain numbers as an absolute, because gain expressed as a deciBel is by definition, relative to a known power source. Thanks, I'm glad you found the diagrams useful. __________________ Thorn "I'm The Doctor. I'm a Time Lord. I am from the planet Gallifrey in the constellation Kasterborous. I'm 903 years old and I am the man who is going to save your lives and all 6 billion people on the planet below... You got a problem with that?"

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