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I am starting to plan a project that involves either an Arduino or Raspberry Pi (haven't decided yet) connected to a number of sensors. The unit will be located outside, battery powered and will send data to a base station located in the house.

I've found a number of different wifi modules that I can connect to Arduino/RPi such as this one, however I'd like to get a bit of an idea of the what sort of range I can expect from the unit.

I understand that there are a number of different variables: whether the transmission is line of sight, the dB gain of the antenna used, etc. However I'd like to get a bit of a ballpark idea of what kind of range I'd expect from units such as the one linked above.

Does anyone know how I can determine this?

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  • \$\begingroup\$ Range will be about the same as with any wifi enabled smart phone - which you can thus use to check your target locations wifi signal strength. \$\endgroup\$ – Turbo J Jan 29 '16 at 9:46
  • \$\begingroup\$ Thanks @TurboJ. I'm also curious about the boost I'll get using an external antenna. I'll check with my phone first and then go from there. Cheers! \$\endgroup\$ – oldo.nicho Jan 29 '16 at 10:31
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Well, exact achievable radio transmission distances can only be determined by on-site measurements (and are still highly variable due to weather). However, I'll try not to make this any more vague than necessary.

The unit you linked has a max. transmit power of +12dbm (about 18mw). For comparison, the most powerful wifi router I just found on a Google search has ~28dbm (800mw). While 800mw may at first seem hugely higher than your 18mw, radio signals decrease exponentially with range, so the dB ratings can be used as a (comparative) straight-line "measuring tape;" meaning that the ~28dBm router would only have about 2.25x the range of your 12dBm chip.

Now, while transmit power may have a relatively tiny effect on usable distance, antennas come in a WIDE difference of relative "powers." Most "normal," router-mounted wifi antennas achieve between 3-5dBi gain. Meanwhile, some of the better commercial antennas (like this one) can achieve 24dBi or better, which means a good (24dBi) antenna on a weak (12dBm) transmitter can "out-reach" a high-power (28dBm) transmitter with a decent (5dBi) antenna by a factor of 36/33.

So, for a short answer, if your cell phone can get a wifi signal from where you want to use your device; there should be no problem just slapping any wifi antenna on that chip. BUT if the cell phone's out of its range, you can add up to ~8x more range to that chip by attaching a high-gain antenna; then nearly double the range again if you install another high-gain antenna on your router (high gain antennas are directionally sensitive, and only work well if pointed straight towards the other transmitter/receiver).

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    \$\begingroup\$ Of course to use a high-gain antenna on your router, it needs to have the ability to attach an external antenna. Many don't. \$\endgroup\$ – tcrosley Jan 29 '16 at 5:10
  • \$\begingroup\$ Holy lack of formatting, Batman! Somebody might want to clean this answer up a bit... \$\endgroup\$ – Kurt E. Clothier Jan 29 '16 at 6:45
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    \$\begingroup\$ Tidied slightly. That's a neat trick with the link, I'll have to find out how all the markup works on this site some time! \$\endgroup\$ – Neil_UK Jan 29 '16 at 8:46
  • \$\begingroup\$ Thanks for the explanation. I guess my best route, as you suggested, will be to use my mobile phone knowing its internal transmitter dBm as an indicator on what kind of range I'll be able to get from any wifi modules I might be interested in purchasing. \$\endgroup\$ – oldo.nicho Jan 29 '16 at 9:02
  • \$\begingroup\$ Also, if you're interested in what markdown is permitted on Stack Exchange sites, check out this page :-) \$\endgroup\$ – oldo.nicho Jan 29 '16 at 9:03

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