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Long range WiFi antenna from Illy coffee can (jgc.org)
169 points by wglb on June 4, 2012 | hide | past | web | favorite | 49 comments

Is the old Pringles can antenna coming back?

ie http://www.oreillynet.com/cs/weblog/view/wlg/448

I've always found USB WiFi cards more convenient because you don't need any special connectors (or soldering skills!):


EDIT: changed the link to "Poor's man wifi" because Google reports malware.

EDIT2: it's worth mentioning that the standing wave ratio using these home-made antennas can be higher than the ratio expected by the device manufacturer.

These returning waves can damage the power amplifier, but with most wireless cards with transmitter power output under 100 mW (IIRC more than that requires a special license in most EU) it's very unlikely (although possible) and it can only happen after continued usage.

Disclaimer: I'm not an expert, just used to play with wireless about ten years ago.

Just FYI, your second link is returning a Malware warning in Chrome.

Thanks, I've changed the link.

Pringles ones are crap, but I can attest to the power of Illys based antennas, having done one exactly like this for a half mile line of site link to a public wifi hotspot about 8 years ago. Eventually I swapped it out for a sky mini-dish with usb wifi dongle and a small biscuit tin lid as a back reflector, as the Illys can dropped out too much in bad weather.

[edit] Woks with usb wifi dongles are also pretty good.

As cool as this is, I'd rather just buy one.

Could someone here recommend a commercial wifi signal enhancer for use with a laptop that they've had good results with? (It need not have a directional antenna as in the original article.)

Whenever I've googled the commercial products, I feel like the market is rife with snake oil. I'd be much happier with a recommendation from someone on HN.

I'm www.netgate.com

The closest thing (though it's completely different) to what is covered in the article is here: http://store.netgate.com/24-GHz-9-dBi-Linear-Feed-Antenna-N-...

The cantennas is really a waveguide. As such, it has no gain. What is being measured is the increase in SNR, due to a lowered noise floor. (Edit: to be completely fair, the antenna raises the signal and noise level.)

This one has increased gain:


Cool seeing the link to Rob Frohne, he was one of my outstanding professors.

To make any consistent results, you need to couple to the RF ouput/input connectors. Nothing you attach to the exterior is going to do what you want - it will change some aspect of the signal, but so does any environmental aspect, including the pipe in the wall next to you.

From my research it is snake oil mostly. The only ones I had any noticeable difference - are cantennas, both home made and production made. The rest - no noticeable difference.

I'd add satellite dishes and woks to the list of things that work pretty well.

Ubiquiti (http://ubnt.com) makes some great wi-fi equipment. One of the pico or nanostation units set to client/station/bridge mode should end any troubles you have. They are incredibly low priced.

I'll second that on http://cantenna.com - Jason and the team there have been providing an excellent source of these antenna's for almost a decade. (I can vouch for the integrity of the product because we were one of the biggest consumers of their product in the day on my site http://netstumbler.com)

I assume that the interest in this is back because of Marius Milner the Google employee who built the Netstumbler software http://www.netstumbler.com / http://stumbler.net is the suspected engineer who wrote the Google software that has been in the news about the mapping of access points by Google streets cars.

In college I built something almost identical to this from a 40oz can of yams, and got a connection to a truck stop wifi a little over a mile away (we had direct line of sight). It actually work pretty well for like 6 months till the weather turned less optimal.

depending on where you were, the truck stop could have been reached with an ordinary 2.2dBi dipole.

Free space loss = 32.4 + 20xLog F(MHz) + 20xLog R(Km) At 2.4 Ghz, this formula is: 100+20xLog R(Km)

one mile = 1.61km, so your free space path loss was around 100dB.

Let's say the truck stop had about the same radio as you, maybe 17-18dBm transmit power (50-62mW) into a 2.2dBi antenna.

Signal leaves the radio at the truck stop at 17dBm, encounters about .8dB of loss in the coax and connectors, and then is raised 2.2dBi by the very short antenna, for 18.4dBm EIRP.

It then encounters 100dB of path loss, arriving at the antenna on your laptop at -81.6dBm, where it is raised 2.2dBi by the dipole in your laptop, and then encounters perhaps another 0.8dBm of losses in the coax and connectors.

The net result: the radio sees -80.2dBm, which is more than enough signal to decode 11Mbps CCK (802.11b @ 11Mbps) or 12Mbps OFDM (802.11g).

So, what you did was unremarkable, though probably fun.

I can confirm that the coffee which comes in those cans is absolutely excellent. Now I have a good use for an empty one.

Pardon my simple understanding of wifi and relays, but could this method be used in creating a wifi mesh system? [1, 2] The relay distance of 1/4 mile could create a mesh network in NYC with minimal cost.

[1] http://code.google.com/p/fabfi/ [2] http://i4bi.org/?p=324

I am not an antenna expert, but one of the things to understand about antenna design is that the shape of the antenna changes its transmission properties. In this case, you end up with a directional antenna.

In the case of a WiFi mesh network, you'd really want a set of omnidirectional antennae. An omnidirectional antenna with a 1/4 mile radius would need a lot more power to operate. Further, in a place like new york, you have to start worrying about 3 dimensions (skyscrapers are tall!) and obstructions (buildings can be difficult for radio signals to pass through).

Edit: removed redundant phrasing.

> In the case of a WiFi mesh network, you'd really want a set of omnidirectional antennae. An omnidirectional antenna with a 1/4 mile radius would need a lot more power to operate. Further, in a place like new york, you have to start worrying about 3 dimensions (skyscrapers are tall!) and obstructions (buildings can be difficult for radio signals to pass through).

The last part (buildings) is incredibly important to remember. WiFi signals—which are typically in the 2.4GHz or 5GHz bands—are extremely susceptible to attenuation in this manner, due to the higher frequency.

Note that, in part, this is why carriers are so hungry for the sub-GHz bands (i.e. 700MHz in the US, 850-900MHz in Australia, etc) for their 3G/LTE+ deployments. The lower frequencies exhibit significantly better building penetration, offset by the need to deploy more cells in order to get similar bandwidth capacity (considered a worthwhile trade-off).

An omni that could broadcast 1/4 mile (400m) in Manhattan at 2.4GHz would need to have a VERY high transmit power. It would likely be illegal, and it would also be dangerous.

2.4GHz in Manhattan? You're making me laugh. There are so many WiFi (and other Part 15.247) devices in Manhattan that the noise floor is sitting around -90dB.

You're not going to build a mesh network in 2.4GHz in NYC.

Or you have an omni antennea for local users and one of these as the backbone link to one of few core routers linked to a decent ISP connection

Don't conflate a strong signal with increased bandwidth. A good "tin can" antenna still isn't going to allow you to exceed 802.11g/n/ac speeds. Chances are you'll still saturate the link.

due to the loss of orthogonality in the channel matrix, you're not going to get anything from 802.11n, other than perhaps the double-wide channels.

No, I'm saying that if you needed a wifi network for say a campsite or outdoors event, or even a private muni-sized network.

You would use a regular omni-antennae for local client connectivity in each zone then a bunch of these to provide the backbone link to connect those zones to some centrally better connected point. Rather than trying to do a pure peer-per mesh

One thing about cantennas is that they are linearly polarised, so you could go from half to full duplex on the same frequency by having four of them, two at either end, rotated 90 degrees apart.

I believe Steve Song's wonderful Village Telco project is about doing just that -- creating a low-cost wifi mesh to share connections. It certainly deserves a mention here!


Just in case someone decide to make one - I have Type N bulkhead connector with probe already soldered into. $10 + actual shipping (I am from Austin, TX) :) hippich@gmail.com

woo.. I'm in ATX, too. I have a warehouse full of 2.4GHz parts. Let me know if you need something. :-)

Since we only recently got DSL, and had to get connectivity before, my city is now covered with wireless networks. Most end-users use "cantennas" (can+antenna=cantenna) made from Nescafe cans. I wonder whether Cantenna term was invented here and whether it is used worldwide?

Anyway, Nescafe cans work very well for access points up to 600 feet away, which covers most of the city. In case Illy is not popular in your area.

I wonder if beer can would work. can increase portability of of the kit. Drink beer, cut the can insert the antenna. Also can use some of those cheap tiny tripods. All that can make a killer traveller wifi kit. I some areas getting reliable signal is such a pain.

According to http://www.turnpoint.net/wireless/cantennahowto.html beer can would be too small. Optimal diameter should be between 3" and 3.66", however some people reported good results with much larger diameters.

this is because all the 'cantenna' does is shield most of the environment, which acts as noise (or interference).

But yes, the opening should be at least 1/2 the wavelength of the signal you seek. The lambda of 2.4GHz is around 0.125m, or 4.9 inches. Half this is just under 2.5 inches.

What does 802.11N change about any of this?

I made a double-long cantenna from some large spaghetti sauce cans years ago and it worked wonders. Then 802.11N became widespread and suddenly all the cards had multiple RPSMA connectors and antennae. Can anyone confirm how 802.11N has changed the recommended use patterns of can antennae? Should I have the same cantenna on each connector, or should they be different to provide differences in signal path for 802.11N magic to work? Could use of (well positioned, well made) can antennas actually make the performance worse than the stock 802.11N setup?

just a few comments:

- the cable for feeding your antenna is quite long. A shorter one would have much less loss - transmission with a directional ant can easily exceed the allowed, effective tx power (i own an Alfa 500mW hooked up to a Biquad with something like 8 to 10db gain and 20cm feed... certainly not allowed in Europe).

- a circular polarized ant is even better for WiFi (multipath interference) but more difficult to build

For a list / how-tos of various WiFi "enhancers" (beer cans, coffee cans, reflectors etc) see http://www.binarywolf.com/249/coffee_can_antenna.htm

(oldest beer can reflector shown is from popular mechanics 1955)

there are also PDFs on the Internet that help you to create your own reflector.

always good fun to make something yourself.

To save money on the SMA-N cable and connectors, I would probably just use a long USB extension cable and put the USB WiFi module directly on the can antenna. Of course this only works where the antenna is not installed outside.

Anyone know where I can find a 1 watt wifi repeater with an input antenna and an output antenna? I'd love to hook up a high gain directional antenna to the input and then an omni directional antenna to the output.

Has anyone tried making a very large cantenna? Like out of an oil drum or something? Would that make it easier to pick up much futher away networks?

I do not think so. AFAIK, size of cantenna and actual probe relates to wave's physical size in order to guide wave. So making it simply bigger will not have benefits

You can use a DSS dish to increase the performance of the 'cantenna'. See link above.

Cool! Is there some significance to the Type N connector, or is it just something that happens to hold the coat hanger wire in place?

Anything will do - the N type is large enough that you can fix the bulkhead to the can wall securely. BNC tend to be a through hole and nut which is hard to fix square to the side of a can.

You can even make a bigger hole and put an entire USB wifi dingle in the can at the correct position but it takes a bit of trial and error because you don't know where the antennea is inside the plastic

I did the same thing when I was young and poor. From my Pioneer Square loft, I got great reception from a cafe a block away.

Anyone had experience with cantennas and HSDPA?

It does leave out the one important thing you need to know - the feed has to be very precisely 1/4 wavelength from the back of the can, about 31mm for 2.412 GHz (channel 1) or 1.2" for US channel 11

To be precise, 1/4 guide wavelength which is different than the freespace wavelength and depends on the diameter of the can. Here is a calculator that can spit out the guide wavelength http://www.turnpoint.net/wireless/cantennahowto.html

Interesting I wouldn't have thought it was such a strong function of can diameter.

Presumably because the can is approx a wavelength you are in all sorts of complex near field regime, unlike say a parabolic sat dish?

Yes that sounds right. The change in wavelength dependence comes from the propagation constant (the argument in the exponential) so the peaks in this exponential are spaced differently than in freespace. The propagation constant changes in order to satisfy the boundary conditions (physically you could think of the wave bouncing at an angle off the sides of the can as it propagates down it) or you can think of it as a way to solve the helmholtz equation, while satisfying the need for the tangential electric field to vanish at the radius of the can.

Holy crap! That actually makes sense. The EM books they are working.

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