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I'd like to increase personal security by receiving Wifi connections 50-100 km away from physical device location, with high decibel to milliwatts (dbm) reading to overcome path attenuation by foliage and other obstacles. This would allow me to avoid the geographical restrictions imposed by the local ISP's Wifi connections, because I would be able to access the internet wherever I please and at any point in the system (within a max 100 km radius).

I'm thinking of using a Yagi directional antenna or maybe a parabolic grid, but the ones I could find so far are significantly limited in range, at 15-20 km max, never in excess of 50 dbm. Where can I find a Yagi or parabolic grid with a range of 50-100 km? Do I need to purchase industrial-grade radio equipment for this kind of Wifi frequency range or is this a DIY project? If it's DIY, what equipment will be needed and are there any guides to building one?

Not at all familiar with RF theory, but can a Wifi range be increased on say a parabolic grid from 15-20 km to 50-100 km?

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    $\begingroup$ You know that you'll need both ends to use a directional antenna, right? If you want increased privacy though, anonymously-purchased and prepaid satellite internet might help, especially if combined with Tor. $\endgroup$ – forest Jan 4 at 3:22
  • $\begingroup$ No, please elaborate. I'm planning on purchasing one in the near future. Wifi signals have been picked up at even lower frequencies than 2.4 GHz and over hundreds of kilometers by satellite dish, so I'm thinking it should be doable. I'm just not sure what equipment/expertise will be needed. $\endgroup$ – piece0fshite Jan 4 at 3:30
  • $\begingroup$ For basic transmission, it should absolutely be possible to get a connection over 100km, but both sides need a directional antenna (usually it looks a bit like a satellite dish) and both need to be pointed at each other with minimal obstacles in between (limited foliage is OK, rocks or dirt is not. Also humidity and rain cut the maximum distance). This means you can't just connect to some free WiFi from Starbucks from 100km away because they are not going to have a directional antenna pointed right at yours. $\endgroup$ – forest Jan 4 at 3:32
  • $\begingroup$ It won't need to be a DIY project as there are absolutely long-range directional antennas, but unfortunately product recommendations are off-topic here. However searching for "long range directional antenna wifi" brings up some good results. Industrial grade? Probably not. But you definitely need a transmitter more powerful than anything a home router can provide to drive the antenna. $\endgroup$ – forest Jan 4 at 3:35
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    $\begingroup$ Surprised that no one mentioned the regulation issue yet. WiFi uses unlicensed spectrum which is overseen by some sort of organization in most global regions. While the use of the frequencies are unlicensed, there are restrictions on the types of devices and they way they can communicate. Even using the high gain antennas you have already found will likely violate your local restrictions on Tx power without reducing the radio power on the AP. It will certainly begin to cause issues with neighboring devices operating in the same frequency range, which will likely get the situation reported. $\endgroup$ – YLearn Jan 4 at 4:29
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As the comments on the question suggest, there are regulatory concerns that may be relevant. But those are dependent on jurisdiction, so let's not get into that. A separate question, tagged with your location, would be appropriate.

Let's focus just on the technical aspects.

There are two concerns with getting a radio link over these distances: radio horizon and path loss.

Radio Horizon

The radio horizon is how far the antenna can "see" before the curvature of the earth gets in the way. Assuming flat terrain, it can be estimated by:

$$ \text{horizon in km} = 3.57 \sqrt{\text{height in meters}} $$

(For a result in miles and a height in feet, change the constant to 1.23.)

The horizons on each end add. So if one antenna has a horizon of 20 km and the other 10 km, the antennas could be up to 30 km apart.

With this equation, you can see to have a chance at a link over a distance of 50 km, you'll need a tower at least 50 meters tall on each end. Unless you are lucky to have one or both of the stations on a hilltop, this alone probably precludes the possibility of a simple DIY solution.

Path Loss

Path loss (assuming no obstructions) can be estimated with the Friis transmission equation to make a link budget. For Wi-fi to have any chance of working at all, you'll need a received power of at least -85 dBm. To have it work well, -60 dBm.

The free space path loss at 2.4 GHz at a distance of 50 km is 134 dB. A Wi-fi transmitter is typically 100 mW or 20 dBm. 20 dBm - 134 dB = -114 dBm, which is 29 dB below the absolute minimum of -85 dBm. That shortfall will have to come from antenna gain and/or amplifiers.

So one solution would be an antenna with 15 dB gain on each end, that would provide a total of 30 dB gain. This is a bare minimum, at the lower end of your "50-100 km" range, and assuming no obstructions. You mention "foliage and other obstacles", which will take additional power or gain to overcome, though realistically by the time you have the necessary 50 meter towers on each end as described above, foliage and obstacles may be much less of a concern.

All kinds of parabolic reflector antennas would be able to provide the necessary gain. A well-built Yagi could work as well.

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