Ten Mile Raspberry Pi WiFi (with A Catch)

How would you like to have a WiFi connection that covers 10 miles? Or how about an even wider network made up of a mesh of multiple nodes? It is possible, but there is a catch: you probably need a ham radio license to do it (at least, you do in the United States).

What makes it possible is the realization that conventional WiFi channels 1-6 are inside an existing US ham band. That means (if you are a ham) you can elect to use FCC part 97 rules instead of part 15 that governs WiFi routers. That means you can use more power and–even more importantly–better antennas to get greater range.

Traditionally, hams have used custom firmware for Netgear routers or Ubiquiti hardware. However, [WZ0W] recently posted his experience using Raspberry Pi boards as mesh nodes. The code (which also works with some other single board computers) is available on GitHub (with details on the project blog). [WZ0W] points out that, unlike using a consumer router, using a Pi provides a reasonably powerful computer for hosting services as well as hosting the network.

There is a video tour of the software in the video below. If you aren’t licensed, you may still be able to use the mesh network firmware, but you’ll have to stick to the stock radios and antennas. If you are not in the US, your laws may be different, so be sure you understand the laws in your jurisdiction.

If you just want a mesh network, there are other options. You can even rip off a conference badge design if you like.

57 thoughts on “Ten Mile Raspberry Pi WiFi (with A Catch)

    1. It sure does. The only case where you’re allowed to encrypt transmissions (or otherwise hide the content) is where you’re sending commands to an aircraft or spacecraft.

      1. It doesn’t seem to say that in the article… it says the intent of the encryption is what is is important… if you are encrypting to obfuscate or change the content of the message it is isn’t allowed, to encrypt in order to maintain the security of the network is allowed.

  1. Doesn’t stop your neighbors getting angsty with you about the 10 watt amplifier you are running your wirfi through, Blowing away everything in a three block radius. so yes, legal, good idea maybe no.

    1. This would be better used in sparsely populated areas anyway. The inverse-square law still applies. Only takes one nearby person with normal WiFi to stomp all over reception of a distant signal, even with 10W TX from the distant node. And since your distant node won’t be able to “hear” that person’s WiFi, there will be no collision avoidance.

        1. I’m pretty sure that’s only the case at lower frequencies. Atmospheric effects keep the signal in parallel with the ground. At higher frequencies I don’t think this happens. Also, the microwave range WiFi operates on I think there’s attenuation from atmospheric moisture, so maybe it’s more like inverse cubed at longer ranges.

    2. Generally you only run that sort of power with directional antennas. If you’re going to achieve that sort of distance, your equipment is going to be on a mountain top or at the top of a tower, not in your living room. Hams are typically aware of how much power to run to traverse a given distance, and how not to interfere with other users on a band.

      1. Look at D-Star and C4-Fusion on ‘gateway’ repeaters… talking to distant locations using a radio and the internet in a “free to operate” manner. Operate the world with a hand-held VHF/UHF radio is pretty neat usage of technology.

    1. Sure you can. Example: If you move into a neighborhood with an HOA you can use your HAM license as a trump card to nearly anything you want to do to your house/yard. You submit your plans for your climbing wall/pool/meat smoking shack to the HOA and when they shoot it down, say “fine, I guess I’ll amuse myself with my other hobby. BRB, constructing a 50′ HAM tower. Oh and before you say no, FCC and federal Civil Defense regs trump anything you have in the covenants and if you try to stop me, one call to the FCC and they’ll make you wish you’d never been born”. This is almost always immediately followed by massive backpedaling and amazingly anything you want to do that isn’t as ugly as a 50′ HAM tower gets approved.

      1. Or, just avoid neighborhoods with HOAs/covenants, and it’s a win-win. I say this as a licensed amateur operator since 1998: It’s not worth the fight, and they’ll eventually find a way to force you out of your home and perhaps even seize your equipment.

        Pro tip: If your neighbors can dictate what color curtains you’re allowed to put up and can take your home away from you if you don’t toe the line, you don’t really own your home. HOAs are for two types of people: Little Hitlers and boot lickers.

      2. This is one thing I don’t understand. People want to live in a fascist run local neighborhood, then complain about the fascism only when it affects them. HOAs should not exist, they’re anti-American.

  2. If I remember correctly, the record for an unamplified wifi link is over a 100 miles, you don’t need an amplifier, it’s all about the antenna ;-)
    Although I admit that 4m parabolic antennas on both sides might be a little impractical :D

    1. You also need to modify the firmware with a longer ACK timeout, to account for the longer time of flight. For collision avoidance, a longer slot time would also be recommended.

    2. “Although I admit that 4m parabolic antennas on both sides might be a little impractical :D”

      yeah, but screw impractical… 4m parabolic antenna would be awesome… or like +20 of them, in a nice little snowflake like pattern on a BIG field

      1. Or if you’re throwing money around, a 500+ element active phased array :D

        But yeah, even one 4m dish would be awesome, too bad they’re becoming rare on the used marked here…

    3. Parabolic antennas at 2.4GHz are rather small. The advantage is big. Distributing and powering a mesh network in suburban area is quite a task which becomes irrelevant for point-to-point links.

    4. that was in South America, one station was near sea level, the other was over 12,000 feet!!!

      ok, they used those big, black, 3 metre “skytv” antennas, but it was still pretty frikken cool!!!

    5. You also, technically, need a license for better antennas. Take the power of your Part 15 radio, focus it into a beam – and you exceed the Part 15 EIRP. Point that beam at the wrong people, and you’re in just as much trouble as if you’d been using a Kw+ amp

  3. “unlike using a consumer router, using a Pi provides a reasonably powerful computer for hosting services as well as hosting the network.”

    Data please ? I’ve had the feeling since I got my Pi that it is one of the slower thing I’ve ever used to make a server. Arduino might be faster.

    1. Which Pi do you have? The original single core Pi and the ones based on it (A+, B+, Zero) are slow at most tasks. The Pi 2, a quad core ARM v7 with 1GB of RAM, is much faster and makes for a decent server. It’s even passable as a desktop machine, though not really practical for that purpose (though that may change with a fully accelerated X driver, if that ever happens). But as server, it’s up to most tasks you can throw at it, and certainly far better than an Arduino and most single-purpose boards like basic routers.

  4. If you are going to do this I would recommend moving the frequency out of the 2.4GHz band, the interference will be way less. You may be able to make your link with much less power. Since you are using linux you can simply edit the kernel to add a few channels below channel 1 (or even simpler, but less professional, edit the driver to offset the output frequency)

    May also want to look into 900MHz gear, which can be used without a HAM license in the US so you can encrypt the mesh.

    1. Modifying 900 MHz RF modules or systems, designed for license-free (pre-certified) usage such as ISM gear, voids the module/system’s licensing, and does require a license for the legal operation of.

      In the US, modified Part 15 modules or systems become no longer Part 15 devices, and thus need a license, (such as amateur radio license under Part 97) to legally be used.

      This includes modifying or replacing the antenna to alter the effective radiated power (ERP) beyond the 100 mW limit in most/all license-free / pre-certified devices.

  5. The diameter of the dish is the biggest factor in gain, the higher frequencies need a smoother surface and more accuracy. It’s easier to get gobs of gain as you go up in frequency.
    Less than 2 meter (12 foot) dishes did one long haul California into Nevada mountains at both ends. They could not so much as log into Yahoo as this amounts to commercial activity, no adverts. They accessed something offline. There is a chart in the ARRL Handbook that shows gain curves with several known radio telescopes above the sizes available to the rest of us with Arecibo topping the chart.

  6. Credit where it’s due…I did not write the code for the mesh node firmware for either the Linksys/Ubiquiti version (www.broadband-hamnet.org) or the Raspberry Pi (www.github.com/urlgrey/hsmm-pi). The heavy lifting was done by developers at those sites. I merely installed them and use them.

  7. How about using 5.8 Ghz? The dishes get smaller, there are more frequencies available and (at least in europe) you are allowed to emmit up to 1 Watt (compared to 100 mW with 2.4 Ghz). Furthermore the fresnell zone gets smaller and (if I’m informed correctly) 5.8 Ghz is less affected by water/rain/fogg than 2.4 Ghz. The 5.8 Ghz frequencies seem to work good because there exist several commercial wireless-link-kits that claim to have a distance of up to 20km (or more) for line of sight .

    @ all the people who discussed about the sence of ham: I’m learning for my ham exam at the moment and you can learn damn a lot about radiowaves and you learn how you can push e.g. your 5.8 Ghz Wlan to the legal limits. (I’m quite sure that ther are regulations in the US, that allow you to emmit even more power if you use directional antennas for long range links.) Unforrunately I haven’t found a similar rule in Europe

    1. The 5.8 band is allowed unlimited gain for point to point links here in the US, it’s a highly preferred band for us wisp operators when the cost of a licensed link isn’t justifiable.

  8. Using any amount of power on 2.4 GHz within the city is not being a good neighbor. If you want to link long distances in sparsely populated areas, that’s a different matter. When I put up a frequency hopper on 2.4, my neighbor reported that his video surveillance system now had lines in the video. I tried various things, but in the end I was not compatible with the neighborhood. I was jamming them, but I was legal. Sometimes legal, is a low bar. “Happy people” (les gens heureux) is is the ultimate goal. Don’t be a WiFi Pig. Share the spectrum.

  9. We used to do this in Australia 10 years ago (I helped as part of Perth Wireless Freenet) and it didn’t require any special licenses. In Australia the limit is 4W EIRP, which you can achieve with a regular 30mW transmitter and a 24dBi directional antenna. We had several links using that equipment up to 10 miles, the only real issue was trying to run point-multipoint and getting hammered by the hidden node problem that comes with CSMA/CA.

    Several proprietary protocols solve the hidden node issue, at the time they were quite expensive but now the super cheap option is Ubiquity AirOS gear. $100 for an outdoor weatherproof PoE unit is ridiculously good value.

  10. More power is not always the best option, better use of the power is a much better idea. I huilt 2 meshed networks in NZ, both were in the 2.4 and 5.8Ghz bands using stock gear except for the antennas and feedlines. We ran links spanning up to 50Km point to point both in the 2.4 and 5.8Ghz region with two NLOS link using 900 Mhz, and one 400Mhz link that was used to punch a link over 4Km through trees and buildings.

    I built all the antennas using waveguide technology and handmade each antenna, we were able to sectorise one of the links and provide a stable 2.4Ghz link to a community over water that was located some 6Km away and the signal was picked up on laptops with no external antenna.

    As time progressed and the 2.4Ghz noise floor increased we started using some more advanced techniques by adding reflectors and a special RF deadening foam to the back of the antennas so as to remove any noise coming in from the rear lobes of the antennas as well as altering the polarization,

    The network was stable and operated for well over 6 years with minimal maintenance however after some silly moves by the local government revoking funding or rather trying to re-write the agreement we had not choice but to pull the plug on the network and walk away.

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