Category Archives: tegnologi

How To Make Waveguide WiFi 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.

1. Collect the parts
2. Drill or punch holes in your can to mount the probe
3. 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 #6×1/4″ 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.

Scientists in Germany have developed next-generation Magnetic Random Access Memory (MRAM) that is said to operate as fast as fundamental speed limits allow.

Scientists in Germany have developed next-generation Magnetic Random Access Memory (MRAM) that is said to operate as fast as fundamental speed limits allow.

By storing large amounts of data at high speeds and preserving stored data even when powered down, the technology could enable instant-boot computers and mobile devices, researchers say. Today’s PCs typically operate on either Static or Dynamic RAM modules (SRAM or DRAM) that store digital information by means of electric charge. SRAMs and DRAMs provide fast access to information. However, in case of power interruption, they lose their stored information, and are thus termed ‘volatile memory’. “Volatile memories [such as] SRAM [and] DRAM lose their information upon power-off,” said Hans Werner Schumacher, who is researching MRAM at Physikalisch-Technische Bundesanstalt (PTB). “That is why you have to wait some time during your PC is booting. During that time the PC is reading the information from the hard disk and writes it into the non-volatile chips on your PC.” Schumacher mentioned Flash memory as an example of non-volatile memory. Flash memory currently is used in some mobile devices such as phones, cameras, and an expanding range of ‘netbooks’ led by the OLPC and Asus’s Eee PC. MRAM is another example of non-volatile memory. Current, first-generation MRAM modules use magnetic field pulses to program magnetic information, and are used in automotive and industrial applications. Instead of using a magnetic field, second-generation ST-MRAM (spin torque MRAM) prototypes use a ‘spin torque’ current pulse to program magnetic bits. A positive current switches the magnetization to one direction (digital state “0”) and a negative current to the other (digital state “1”). Normally, the magnetization has to undergo several precessional turns before reliable magnetization reversal takes place, so ST-MRAM is estimated to be a factor of 10 slower than the fastest SRAM technology. However, using a new technique known as ‘ballistic switching’, Schumacher and his research team were able to achieve reliable magnetization reversal in a single precessional turn. Researchers expect future MRAM based on ballistic spin torque reversal to achieve write clock rates well above 1 GHz.  “In our work we show that one can optimize the programming of the bits by proper selection of the parameters of the current pulses used for programming the bits,” Schumacher told iTnews. “This allows [devices] to reliably write the bits by pulses of only one-nanosecond duration. Using this technique future ST-MRAM [Spin Torque MRAM] could operate as fast as the fastest volatile memories.” Compared to first-generation MRAM, ST-MRAM can be scaled down to very small sizes, thus promising high storage densities comparable to DRAM and Flash. “In the future ST-MRAM has a very broad field of applications,” Schumacher told iTnews. “They are fast, have a high storage density, and are non volatile … present memories do not offer this combination of features.” “Here, first gigabit prototypes have been produced. However these ST-MRAM are not yet in production.” “Like in all new technologies some technological issues still have to be solved before market introduction,” he said.