[webtechgal]

> some do 500mW you can multiply that if you add custom antennas...

I am somewhat confused here. How can an antenna (a passive device) multiply (or amplify) the power? Yes, it can effectively increase the range by allowing the signal to propagate farther, but actually multiply the power? I don't think so, unless it also includes a signal amp/booster.

[datenwolf]

The term "gain" is a bit unlucky, because it does not really describe what's happening. A much better term would be "directivity". Antenna gain is always with respect to a reference pattern; usually a perfectly omidirectional isotropic pattern is assumed and the gain tells you, how much of the antenna radiation pattern is "compressed" into the spatial direction you're looking at, compared to a plain isotropic antenna.

For example if you're looking at a plain old dipole antenna, then in the plane perpendicular and centered around the dipole you'll see a +5dB gain as if the antenna was perfectly omnidirectional. But if you move out of the plane, say right into the axis of the antenna (but some distance away) there will be very few signal, so what would have gone there has been redistributed into a different spatial direction.

Now consider you have a wireless device sending with 20dB(mW) = 100mW and attach an antenna with a directivity gain of 20dB to it. Then to a receiver that happens to be located within the directivity pattern it looks as if there was a transmitter sending with (20 + 20)dB(mW)=100*100mW = 10W through an omnidirectional radiator.

It's one of the few cases where English is lacking a distinctive term. In German the term used for antenna gain is called "Gewinn", whereas amplifier gain is called "Verstärkung".

[dogma1138]

RF is a bit more complicated than that, you have also a specific gain on an antenna. https://en.wikipedia.org/wiki/Antenna_gain

The gain on the antenna doesn't create "energy" but it tells you how efficient an antenna is and what its RF characteristics would be, in general a high gain antenna is a directional one it would send a more focused transmission and would attenuate better to a receiving transmission from a certain direction only, a low gain antenna would have a more uniform RF profile (doughnut/spherical).

High gain antennas are usually used for point to point applications so MW transmitters, P2P Wifi Links, TV/Satellite etc. while low gain antennas are used in devices where the transmission can come from any direction like for example GPS receivers, cell phones and handheld radios.

For Wifi for most applications you would want a low gain antenna on your routers/AP's as they would give you uniform coverage, people often buy high gain antennas without understanding what it means, it's great if you want to line of sight 2 AP's across long distances but unless you also want to line of sight your XBOX it wouldn't have any positive impact on your wifi reception at home.

[nisa]

you are correct. sorry. here is a link that explains it well: http://www.tp-link.us/FAQ-3.html

I was refering to the ERP - in the article:

> Even the law states [wrongly] that the "Effective Radiated Power (ERP) will not exceed..." and this is based on the input into the antenna multiplied by the antenna gain.

So you are correct! Thanks for pointing that out!