
Long range WiFi antenna from Illy coffee can  - wglb
http://blog.jgc.org/2012/02/long-range-wifi-antenna-from-illy.html
======
reidrac
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!):

[http://www.instructables.com/id/%22Poorman_s-WiFi%22--USB-
ad...](http://www.instructables.com/id/%22Poorman_s-WiFi%22--USB-
adapters-%26-DIY-cookware-refl/)

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.

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

~~~
reidrac
Thanks, I've changed the link.

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alister
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.

~~~
gonzo
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-...](http://store.netgate.com/24-GHz-9-dBi-Linear-Feed-Antenna-N-
Female-P337C42.aspx)

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:

[http://people.wallawalla.edu/%7ERob.Frohne/Airport/Primestar...](http://people.wallawalla.edu/%7ERob.Frohne/Airport/Primestar/Primestar.html)

~~~
K2h
Cool seeing the link to Rob Frohne, he was one of my outstanding professors.

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pbnjay
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.

~~~
gonzo
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.

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

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startupfounder
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>

~~~
etrain
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.

~~~
elithrar
> 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.

~~~
gonzo
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.

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hippich
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

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

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babuskov
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.

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perlpimp
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.

~~~
nawariata
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.

~~~
gonzo
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.

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beemoe
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?

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rauar
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

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fpp
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.

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K2h
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.

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phasevar
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.

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TamDenholm
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?

~~~
hippich
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

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

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jakejake
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?

~~~
excuse-me
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

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alexgrande
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.

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skeletonjelly
Anyone had experience with cantennas and HSDPA?

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excuse-me
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

~~~
johnnylawrence
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>

~~~
excuse-me
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?

~~~
johnnylawrence
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.

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

