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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?

  • This news article mentions a Blackhat talk which discusses it, but it's not "easy". –  Jan 04 '19 at 03:54
  • @forest, maybe in some jurisdictions. From the FCC standpoint for 2.4GHz there are different rules relating to fixed point-to-point. Since this isn't a fixed point-to-point installation, this will still be considered a point-to-multipoint installation which the FCC limits the EIRP (equivalent isotropically radiated power) to 36 dBm (or 4 watts). Antenna gain (especially for WiFi) is typically measured in dBi (decibels relative to isotropic). Notice both are measured against the fictitious isotropic radiator. So a gain in dBi requires a reduction in radio Tx power to maintain an EIRP of 36 dBm. –  Jan 04 '19 at 04:56
  • The article says that anyone can access satellite internet with a PCI satellite collector card and certain Linux DVB programming apps, which remain unspecified. Wireshark is mentioned, a Kali OS tool, but that's not sophisticated hacking unless knowledge of high-level programming languages are involved, like C++. Is a DVB device also needed, in addition to the apps? Where could I find further details about this setup? –  Jan 04 '19 at 04:48
  • @YLearn I think there may be exceptions if it's directional, but I'm not sure. However it's moot anyway since in some jurisdictions, attempting to hide your location with a radio transmitter is illegal, period (which is silly, I know). –  Jan 04 '19 at 04:34
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    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. –  Jan 04 '19 at 04:29
  • Also another technique you can use is with GSM/LTE, if you make sure you are within range of only one cell tower, to prevent triangulation. It's cheaper to get anonymous cellular internet than satellite internet. –  Jan 04 '19 at 03:56
  • I must say that I'm intrigued. You may be on to something. I looked at that comment and it mentioned something about guides and needing satellite equipment to anonymously obtain satellite internet. Care to elaborate? –  Jan 04 '19 at 03:52
  • Just to add some other aspect to the discussion: at 2.4 Ghz the RF signal is mostly a straight line and the world is not flat (really). This means one need to have a very high antenna (>600m) if the destination is at the ground) to achieve the 100km. This is very likely noticeable and maybe even illegal to install. See Line of Sight Calculator. –  Jan 04 '19 at 05:28
  • Depending on the level of anonymity required, you can probably buy prepaid satellite internet with cash in many remote areas (satellite internet works pretty much everywhere, so you don't need to stay in said remote areas). And of course if you're feeling adventurous, you can reverse engineer the transmission protocol and get free satellite internet, but that requires some firmware and protocol hacking. –  Jan 04 '19 at 03:47
  • Yeah that's not going to work. Although your transmitter could certainly send a signal that far, there is no way it could possibly receive transmissions from such a weak transmitter so far away. Also, because it would be directional, it would be easy to locate you. I would recommend using satellite internet instead (prepaid and anonymously obtained), since it's a lot harder for a satellite to locate you in the air than it is to locate you on the ground. I don't know what services allow you to do that. You'll have to get creative. –  Jan 04 '19 at 03:45
  • I see. Having another antenna elsewhere would be a bad idea. Would a parabolic grid involve the same kind of setup? I was thinking that anonymously using an ISP or free Wifi connection hundreds of kilometers from the actual device would maximize privacy and anonymity, bringing one as close as possible to 100% untraceable. You would have an IP but it would be in totally different geographical location. Further, you mention prepaid satellite connection, but that would leave a money trail, unless you can pay with crypto. But what service allows you to do that? –  Jan 04 '19 at 03:41
  • 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. –  Jan 04 '19 at 03:35
  • 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. –  Jan 04 '19 at 03:32
  • 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. –  Jan 04 '19 at 03:30
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    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. –  Jan 04 '19 at 03:22
  • See also: https://security.stackexchange.com/a/200155/165253 –  Jan 04 '19 at 03:46

1 Answers1

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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.

Phil Frost - W8II
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