антенна
How to build a tin can waveguide antenna
How To Build A Tin Can Waveguide WiFi Antenna
for 802.11(b or g) Wireless Networks
or other 2.4GHz Applications
click on image to enlarge
Got no dough for a commercial WiFi antenna?
Looking for an inexpensive way to increase the range of your wireless
network? A tin can waveguide antenna, or Cantenna, may be just the
ticket. This design can be built for under $5 U.S. and reuses a food,
juice, or other tin can.
I am not an electrical engineer, nor do I have access to any fancy test
equipment. I've built some antennas that worked for me and thought I would
share what I learned. I have no idea if this is safe for your radio or
wireless network equipment. The risk to you and your equipment is yours.
Building your Cantenna is easy, just follow these steps.
Collect the parts
Drill or punch holes in your can to mount the probe
Assemble the probe and mount in can
Collect the parts:
You'll need:
A N-Female chassis mount connector.
Four small nuts and bolts
A bit of thick wire
A can
These vendors can supply the parts (the wire and can
you provide yourself).
The Connector
A N type Female Chassis-mount connector. One side is N-female
for connecting the cable from your wireless equipment, and the other
side has a small brass stub for soldering on wire. These can be
found at electronics stores internet suppliers (see the list below
under "Connect your antenna..." If you shop around, you
should be able to find these for $3-$5.
Nuts & Bolts
You'll need them just long enough to go through the connector and
the can. I've used #6x1/4" stainless. If your N-connector is
a screw on type, then you won't need the nuts and bolts.
Wire
You'll need about 1.25" of 12 guage copper wire. This wire
will stick into the brass stub in the N-connector.
A Can
This is the fun part. You're looking for a can between about 3"
and 3 2/3" in diameter. The size doesn't have to be exact. I
made a good antenna with a Nalley's "Big Chunk" Beef Stew
can that was 3.87" in diameter. Others have reported good results
with big 39oz. coffee cans that are 6" in diameter. The pringles
can is really too small for good performance, however. Try to get
as long a can as possible. The old fashioned fruit juice cans should
work well.
Click on image to enlarge
Drill or punch holes in your can to mount the probe
The N-connector assembly will mount in the side of your can. You need
to put holes in the right place to mount the connector. The placement
of the hole and connect is very important. It's location is derived from
formulas that use the frequency that the antenna will operate at and the
can diameter. To make life easy on you, here's a calculator to figure
it out for you.
Can Diameter
Cuttoff Frequency in MHz for TE11 mode
MHz
Cuttoff Frequency in Mhz for TM01 mode
MHz
Guide Wavelength in Inches
inches
1/4 Guide Wavelength
inches
3/4 Guide Wavelength
inches
Enter the diameter of your can above and click on the calculate button.
802.11b and 802.11g WiFi networking equipment operates at a range of
frequencies from 2.412 GHz to 2.462 GHz. Ideally, with your
can size, the TE11 cut-off frequency should be lower than 2.412 and
the TM01 cut-off should be higher than 2.462. It would be good, also,
if your can is longer than the 3/4 Guide Wavelength. If your can is
a little off in length or diameter, don't despair, experimentation
is fun!
You want to mark the location on the can where you will put the hole
for the connector. The 1/4 Guide Wavelength number tells you how far
up from the bottom metal end of the can to put the center of the hole.
Open only one end of your can, eat the contents, and give it a good
washing. You'll probably want to remove the label too. Use a ruler to
measure up from the closed end 1/4 Guide Wavelength and mark the can
with a dot.
If you've got a drill, select a bit that matches the size of the center
of your connector. You may want to start with a small bit and work the
hole larger and larger. You could even start with a hammer and nail,
then use drill bits. If you don't have a drill, start with a nail hole
and use a file to get the hole to the required size. If you're using
a bolt on connector, make four more holes for the bolts - you can use
the connector as a drilling guide.
Click on image to enlarge
Assemble the probe and mount in can
Now you'll need that bit of wire. You'll need a soldering iron or a friend
with one as well. Cut the wire so that when it is stuck in the connector
as shown, the total length of both the brass tube and wire sticking out
past the connector is 1.21". Get as close to this length as you can.
When you've got your wire correctly sized, solder it into the connector
keeping it as straight and upright as you can. When it's cooled, bolt
or screw the assembly into your can. Put the heads of the bolts inside
the can and the nuts on the outside to minimize the obstructions in your
antenna. Your Done!
Connect your antenna to your wireless card or access point
To use your cantenna, you'll need a special cable commonly called a "Pig
Tail". The pig tail connects your wireless card or access point to
you antenna. One end of the cable will have a "N" Male connector
(just right for connecting your your cantenna), while the other end will
have a connector appropriate to your card or access point. For a good
picture of a pig tail, take a look at:
http://www.seattlewireless.net/index.cgi?PigTail
You'll want to have a wireless NIC or access point with an external antenna
connector. Otherwise, you may have to hack into the one you have to hook
up the cable. I wouldn't recommend this unless you're good with a soldering
iron and electronics. For this reason, I like the Agere Orinoco cards
which have a nice antenna connector. Pig Tails can be hand made if you
have the right tools, but it's probably easier to get a pre-made one.
Try:
Fleeman Anderson & Bird
Fleeman Anderson & Bird has a "cantenna kit" for sale
that includes the connector and pigtail. Choose one of the "cables"
links from the menu and look towards the bottom of the list.
Hyperlinktech
Antenna Systems
Hook up your cable, point the antenna at a friend's, and see how far
you can stretch you network. Be sure to let me know (greg@turnpoint.net)
how it works.
This antenna has linear polarization. That means that how you rotate
the antenna will affect the strength of your signal. Usually, you will
want to put the connection straight down, but experiment with rotating
the can while watching the signal strength on your PC to get the best
performance.
For more information, check out these resources:
The ARRL Antenna
Handbook
A Tin Can
Design with good theory information.
A free on-line book
on microwave antennas
"Juice
Up" your Tin Cantenna with a surplus satellite dish.
Spreadsheet
for optimum can size calculation
Go to the Homebrew WiFi Antenna Shootout
Go to the Wireless Home
Click on images to enlarge
Copyright 2003-2007 Gregory Rehm - All rights reserved.
For information about reproducing this article in any format,
contact the author: greg@turnpoint.net
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