antennas

davidclayton

a router/ap i'm looking at has a 2 dBi gain iccle antenna,
and you can replace it with an external 9 dBi outdoor antenna if you want.

what is the relationship of dBi?
is it 4.5 times stronger?
or does it work on a logarithmic scale?
[as with speaker wattage]

dave:rolleyes:

lynchie

Its logarithmic based the same as watts. A 30dbi antenna pumps out 1W while a 20dbi antenna pumps out 100mW.

davidclayton

i;m still confused...

so its way more than 4.5 times
more powerful???

dave

oscarBravo

It's not so much "more powerful" as "more focused" - antenna gain can't increase the power of the transmitter, but concentrates it into specific directions. A high-gain omni works by reducing the signal available above and below it, and increasing the signal roughly in a horizontal plane around it.

Every 3dB of gain doubles your signal strength. A 9dB antenna is 5 times more useful (in its peak direction) than a 2dB [ 2^((9-2)/3) ] unless my understanding is way off.

davidclayton

i need the vertical signal
[to service 3 floors]
so it's not a good idea to get that antenna then??

dave

oscarBravo

Originally posted by davidclayton
i need the vertical signal
[to service 3 floors]
so it's not a good idea to get that antenna then??

Not if it's an omni, no. If it's a planar type of antenna, then it achieves gain by focusing the signal in a particular direction. A 9dB planar (like this one) has a beamwidth of 50x75 degrees. Mounted at the top of a building, pointing straight down, it should give you the coverage you need.

That depends on the building's construction, of course - timber floors tend not to be a problem, but concrete is a disaster.