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It’s all about the fractals: How goTenna designed its off-grid messaging device

goTenna is only a few months away from shipping its first device, a messaging baton that can communicate in places where cellular and Wi-Fi signals don’t tread, but it’s still putting the finishing engineering touches on its design. In particular, co-founder and CTO Jorge Perdomo and his team have been spending a lot of time playing with fractals.

No, I don’t mean Mandelbrot inkblots. Rather, Perdomo is tinkering with fractal designs in the goTenna’s antenna, creating a device that can tune itself to account for even minutest changes in radio frequency conditions. Instead of a psychedelic image out of a Pink Floyd laser light show, it resembles a squiggly line.

GoTenna fractal antenna
One of goTenna’s fractal antenna designs (image: goTenna)

Fractal antennas themselves are nothing new, and have been used in all kinds of communications networks. In mobile communications, fractal designs have eliminated the antenna stub by wrapping the length of antenna into a meandering line or arrays or repeating shapes. But the biggest advantage such designs have brought to the smartphone is the ability to tune itself to different wavelengths by changing the radiating patterns of the antenna.

We see the result of these advances every year as each successive generation of iPhone, iPad and the various Android flagship devices emerge. They’re able to support an increasing number of global LTE bands in a single device. Device makers aren’t merely packing dozens of antennas into their phones, rather they’re using new antennas that can shape themselves to dozens of different frequency bands used across the world.

What’s in a wavelength?

goTenna isn’t building a wavelength-hopping smartphone. It’s doing the exact opposite, designing a device that transmits minuscule amounts of information in a single frequency band. What’s more, goTenna works in some pretty adverse conditions. There is no high-powered cellular network transmitting to goTenna batons from high up on a tower mast. Instead, goTenna devices transmit directly to one another, sending text messages and GPS coordinates through wilderness or over ocean waves.

So instead of using fractal designs to get the most band flexibility out of his gadget, Perdomo said, he’s tapping fractals to optimize the radio experience within the narrow confines of goTenna’s chosen radio band. The Multi-Use Radio Service, or MURS, has only 100 kHz of usable capacity, compared to the hundreds of megahertz available to cellular and Wi-Fi services.

goTenna pairs with an iOS or Android device allowing them to send messages and GPS coordinates to other goTenna users  (image: goTenna)
goTenna pairs with an iOS or Android device allowing them to send messages and GPS coordinates to other goTenna users (image: goTenna)

goTenna is trying to squeeze a lot out of that band. Since there is no network intermediary to carry its traffic, goTenna has to transmit over miles of terrain, otherwise it would be useless to the hikers, hunters and other outdoorsy folks goTenna wants to target. But goTenna also has to transmit at very low power because in the thick of the forest or on the sides of cliffs, there aren’t many wall sockets to give the baton a quick charge.

Consequently, Perdomo and his crew are trying to find a fractal design that will turn goTenna into the most efficient transmitter and receiver possible within the MURS band. So while a phone maker would use fractals to create a device that does an adequate job tuning itself to as many bands as possible, goTenna is using the same principles to tune itself to the optimal frequency within its own band, Perdomo said.

You can think of goTenna’s antenna like a track-and-field star that specializes in a single event like the 100-yard dash as opposed to the more versatile decathlete.

Cruising with goTenna — literally

Perdomo said his team is still finalizing the fractal design that will wind up in goTenna, but the company still has plenty of lead time before they need to be manufactured. Speaking of manufacturing, goTenna CEO and co-founder Daniela Perdomo (she’s Jorge’s sister) told me that goTenna has far exceeded its goal from its preorder campaign, and is on track to ship its first devices in the first quarter.

Jorge and Daniela Perdomo, siblings and co-founders of goTenna
Jorge and Daniela Perdomo, siblings and co-founders of goTenna

Though she wouldn’t say just how many orders goTenna has received, Perdomo did reveal that buyers are coming from some unusual quarters. There’s been a lot of interest from the hiking/trekking/hunting crowd and from privacy advocates that want an off-the-radar communications option. But that interest was expected. What surprised the Perdomo is the number of people purchasing the device that work or vacation on cruise ships.

If you think about it, cruise ships make perfect sense. You’re far away from any land-locked cellular network, and the only option for texting is a spotty and expensive satellite service. So next year if you happen to be on your deck chair aboard the Pacific Princess using goTenna to invite your spouse to poolside cocktails, remember one thing: you owe it all to fractals.

5 Responses to “It’s all about the fractals: How goTenna designed its off-grid messaging device”

  1. Most people know so little about RF. First off, I don’t see much fractal nature in the folded design shown. Secondly, the reviewer thinks(was led to believe?) that huge range without cells would now be possible. No. To have long range, you need either a lot of power, or high gain in the antenna, or both. To get high gain in an antenna, you have to make it very directional to get the high gain. And you have to aim it carefully, since it will be a very low gain antenna in all other directions. All that assumes we’re talking about operating in the clear, buildings and terrain will still block any antenna, that’s why you need high repeating stations like cell sites every few miles, for the frequencies used. Cruise ships? Can’t imagine they don’t have their local WiFi, cell, etc sites, already, and any one of those probably won’t work at all below decks, inside all that shielding metal, unless they set up tiny cell repeaters on every deck.. Two of these would NOT work well, unless both are without much in their way.

    And why do you think a higher wattage radio would not make any difference? Received power IS the transmitted power (including antenna gain) minus the path loss. You can only go so far with that. I’m amazed they got 2 W from the FCC.

    Anyway I do go on, but I hate to see marketing try to supersede physics, or people who don’t know the facts get glossed over by the marketeers, and repeat such stuff.

    If will work, over a variety of close, line of site distances, and be blocked by many objects and terrains. Real world performance will be, it depends. But not “across ocean waves”.

    • Hey JP,

      JP here again as well from goTenna. Your comments are good, you know your RF which most people don’t! You’re absolutely right that higher power and directional antennas would allow us to great greater range and whatnot, but unfortunately power is limited by the FCC and we can’t go directional in a system that is designed to be mobile.

      Your concerns about possible obstructions and the like are valid, which is why we try to take care to point out that our larger-end ranges come when you’re in more ideal environments, but that’s also not to say that it won’t work in obstructed environments too. The only place I’ll disagree a bit with you on, is that line-of-sight is required. Although it certainly helps, these VHF bands have a certain level of diffraction and penetration in the wave propagation characteristics that allow links to be established even when LOS isn’t available. For example, we’ve run tests diagonally through buildings in NYC and have achieved 0.5-1 miles, which is pretty great considering its a canyon of concrete and steel.

      Unlike some other consumer-oriented RF companies (24 miles on a FRS radio? please!), we really want to be very honest and straightforward about what is or isn’t possible, which is why we outline all of this clearly on our How It Works page. We haven’t broken the laws of physics (I wish!), but we’ve developed a very high power, small, light, and easy to use product that marries the best of portable RF with the usability of the modern smartphone. This won’t get you HBOGO while in the middle of the Atlantic (again, I wish), but it will help you communicate in a lot of situations when you normally couldn’t.

      Best,
      Jorge

    • A higher wattage radio would certainly help, but unfortunately the FCC places a limit on what we can do and still make this a consumer product that doesn’t require licensing to use! Even so though, 2W is quite a lot of power, a lot more than you get in normal consumer radios such as those bubble pack radios you might get at RadioShack or whatnot!