How to determine the gain of your DIY antenna?

[cooper]

So you've gone into full MacGyver mode and made your own antenna using some pieces of string, a wad of bubble gum and your trusty swiss army knife and lo and behold, the damned thing actually works...

Now, you can obviously compare your homebrew antenna with any other by simply aiming it (assuming it's directional) at an AP and comparing the link quality using whatever tools and metrics you want. But how do you figure out what the actual gain of that antenna is?

I've read one website that suggest it's a matter of taking your new antanna N, a second antenna G of which you know the gain it has and an accesspoint AP and set them up in a V pattern where the distance for both antennas to the AP is identical, take the S/N for the G antenna in this setup and the S/N for the N antenna and then compute the gain.

My problem with this would be that I don't actually have a good known gain antenna. Just some flimsy low gain El Cheapo 'came with the device' type antennas.

Is there an alternate way?

[madhak]

There's many way to do that, but it require some tools like a RF Power Meter and an RF Attenuator. Don't rely on the wifi signal strength because its a composite of many variable and doesn't tell the full story. A WiSpy device could help as it will provide the raw IQ you need to evaluate the signal strength. the Attenuator will allow you to test on smaller scale so you don't have to walk long distance to reach the end of signal.

The radiation pattern will depend on the type of antenna you build, so google "the type of antenna you build" and radiation pattern, and you will find that it look like. i.e: whip, dipole, turnstile, patch, yagi, dish...

If you really need to measure the radiation pattern then you need a special RF proof room with an array of power meter, you can rent those kind of room but its not cheap! of try to find a place with the least amount of RF interference, but these are rare nowaday, if your cellphone as signal its likely that its not a good place to test!