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.

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:

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 ( 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.


RIM looks to be keeping its nose above the competition in the face of a slowing market for smart

RIM looks to be keeping its nose above the competition in the face of a slowing market for smartphones.

By Reuters, 8 Sep 2008 at 14:34

Gartner said Research In Motion (RIM) were the winners in a slowing smartphone market during the second quarter, doubling its market share to 17.4 per cent.

The market was still dominated by Nokia, which sold 15.3 million phones with capabilities like e-mail and navigation, giving it a 47.5 percent share. But this was down from 50.8 percent a year ago as competition intensified in the consumer smartphone market.

“RIM continued to execute well at the consumer level, increasing its global market reach,” Gartner analyst Roberta Cozza said in a statement.

RIM sold 5.6 million smartphones in April through June, up from 2.5 million a year ago, as it found new clients beyond its main business market.

“In the second half of the year, the company is expected to launch smartphones based on new (designs) … which are necessary to keep pace with the competition at the consumer level,” she said.

Gartner said Nokia needs to introduce more design variations among its N-series multimedia phones to stay ahead. The company has only tweaked its N-series lineup so far this year and many analysts expect it to lose more market share in smartphones in coming quarters.

Credit Suisse said it expects Nokia’s smartphone market share to fall to 41.6 percent in 2009, hurting profit margins.

“Longer term, we maintain our concerns regarding smartphone share in the face of new competition from the likes of RIM, Apple and HTC (High Tech Computer),” analyst Kulbinder Garcha at Credit Suisse said in a research note.

Gartner said global smartphone sales growth almost halved from the first quarter to 15.7 percent.

“The current economic environment continues to negatively impact the market, limiting consumer spending and replacement purchases in general,” Cozza said, adding growth should pick up again in July through September.

“Wider availability of new touch smartphone models together with the global introduction of the iPhone 3G will help sales of smartphones return to stronger growth in the third quarter of 2008,” Cozza said.

Apple’s share of global smartphone sales fell to 2.8 percent from 5.3 percent in the first quarter of 2008 as it sold down inventories of first-generation iPhones before the launch of the iPhone 3G.

HTC sales more than doubled from a year ago to 1.3 million phones, lifting the company to No. 3 position from seventh place the previous quarter.

In smartphone operating systems, Symbian lost market share as the Japanese market declined and Mitsubishi exited the market. Symbian had 57 percent of the market in the second quarter, compared with 66 percent in the same period last year.

RIM had 17.4 percent of the market and Microsoft’s Windows Mobile market share stood at 12 percent in the quarter.

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.

With Child, With Cancer


With Child, With Cancer


Published: August 29, 2008
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LIZETTE IRVIN, HEAVILY PREGNANT, reclined on a hospital bed, relaxed, considering the circumstances. A bag of fluid dripped into her blood through an IV line as Irvin sucked on ice cubes, trying to pass the time. The ice helped to minimize the metallic taste and heat in her mouth from 5-fluorouracil, an antimetabolite, which entered her bloodstream via a catheter inserted in her chest. It was June 16, Irvin’s fourth round of chemotherapy. She was 32 weeks pregnant and had breast cancer.

Dan Winters

Lizette Irvin had four rounds of chemotherapy while pregnant.

Jeff Wilson for The New York Times

Lizette Irvin at home with her newborn daughter.

Before she left the chemo suite at the M. D. AndersonCancer Center in Houston, Irvin, who is 36 years old, was hooked up to a portable pump that slowly released doxorubicin — “the red devil,” a drug so toxic it can cause third-degree burns — into her body over the next 72 hours. During that time, her daughters, Madeline, 4, and Noelle, 2, stayed at her in-laws in part because Irvin feared that Noelle, “the clingy one,” might accidentally tear out her IV.

It was Noelle’s clambering on her mother that first alerted Irvin to a tender lump in her left breast last November. Irvin nearly called off her mammogram appointment when a home pregnancy test showed up positive in December. Because pregnant women typically experience enlargement and tenderness of their breasts, they often ignore early signs of cancer. Unfortunately, this means pregnant women learn of their breast cancer 2 to 15 months later than nonpregnant women and are two and a half times more likely to be told they have advanced-stage cancer. (Irvin’s cancer was Stage IIB; she had three smalltumors in one breast and the cancer had begun spreading to her lymph nodes.) Doctors are discovering more and more breast cancers at Stage 0 and I in nonpregnant women, but as one oncologist, Dr. Clifford Hudis, chief of breast-cancer medicine at Memorial Sloan-Kettering Cancer Center, put it, “In pregnant women, breast cancer is more likely to be the old-fashioned, 19th-century, ‘look at this big thing that’s developed.’ ”

In Irvin’s case, a breast specialist was concerned enough by an initial ultrasound that Irvin had a biopsy and mammogram right away. For the next few days, she focused intently on her daughters’ play dates, Madeline’s upcoming birthday party and “pushing the negative away.” On the fifth day, a nurse called and asked her to come in — and to bring her husband. “It doesn’t take a rocket scientist,” Irvin told me, but when the surgeon told them she had cancer, “I went completely blank.”

The question of how to handle cancer during pregnancy has long troubled the medical profession. In 1880, Samuel Gross, a pioneering American surgeon and the subject of the celebrated Thomas Eakins painting “Gross Clinic,” noted that when breast cancer was associated with pregnancy, “its growth was wonderfully rapid and its course excessively malignant.” In 1943, after treating 20 pregnant patients for breast cancer, doctors atColumbia-Presbyterian Hospital concluded that pregnancy made the disease inoperable. Ten years later, the consensus was that termination of the pregnancy was essential and even improved patient survival.

Breast-cancer treatment has made huge strides since then, and a considerable amount of research shows that termination does not improve a pregnant woman’s prognosis. Yet many pregnant women are still refused treatment unless they abort. “Some doctors may be concerned about hurting the baby or the mother,” says Dr. Richard Theriault, an oncologist at M. D. Anderson, where he oversees a team specializing in the treatment of pregnant women with breast cancer. “Or they’re concerned there will be some medical catastrophe and they’ll be liable. Some just don’t want to tackle the issue because it’s complicated.”

Though still relatively rare (the rate of pregnancy-associated cancer is about 1 in 1,000 pregnancies), the incidence of pregnancy-associated breast cancer is considered to be on the rise. Cancer is primarily a disease of aging, and in the case of breast cancer — the most common cancer diagnosed during pregnancy — age works against women in two ways. First, studies show that women who give birth for the first time at younger ages are less likely to get breast cancer. (The best, perhaps only, argument in favor of teenage pregnancy is that women who get pregnant before age 20 are two to three times less likely to develop breast cancer than women who get pregnant for the first time after 30.) Second, as women increasingly conceive for the first time in their 30s and 40s, their likelihood of developing cancer while pregnant increases. Only 2 percent of breast-cancer cases occur in women under 35, but 1 in 5 are diagnosed in women between the ages of 35 and 49. It’s at these ages that cancer and pregnancy are most likely to collide. One study showed that among women 35 and younger with cancer, 14 percent were pregnant when their illnesses were diagnosed; another study of women under 45 found that 7 percent were pregnant at the time of diagnosis.

All this takes place against the backdrop of a massive biological shift. Only 150 years ago, girls got their first period at 15 or 16 and went through menopause in their late 30s and 40s. Today, girls begin puberty as early as 9, and menopause generally occurs around 50. We have also increasingly begun tinkering with our bodies, pushing the limits of our fecundity through an array of assisted reproductive technologies. The period in which women’s bodies go through a series of tremendous hormonal shifts is extending ever longer, increasing both our fertile years — and our chances of getting breast cancer.

Lizette Irvin hadn’t even planned to get pregnant. Twelve weeks in, when her cancer was diagnosed, she fleetingly considered terminating the pregnancy. “But it wasn’t really an option,” Irvin said, citing her Catholicism. The breast specialist she initially consulted was surprisingly optimistic. “Despite what you might think, chemo is an option,” she was told.

As best they can, oncologists try to hew closely to the level of care a nonpregnant woman would receive. “The decisions you have to make when a woman has cancer are difficult enough,” Dr. Ann Partridge, an oncologist at Dana-Farber Cancer Institute in Boston, says. “Throw in the fact that she’s pregnant, and now we have another party to think about, the fetus.” Most oncologists advise strongly against chemotherapy in the first trimester when the fetus’s organs are developing. Irvin, like nearly all pregnant breast-cancer patients, had a mastectomy and then started chemo at 23 weeks. She was determined to be aggressive. “I was ready to get rid of both breasts, but they told me it wasn’t really necessary at that point.” The doctors also wanted to keep her underanesthesia for as little time as possible.

“People can fathom what it’s like having two children under 5,” Irvin said. “They can fathom being tired because you’re pregnant. They can even fathom what it’s like having cancer. But they cannot fathom all three at the same time.”

IN 1997, WHEN Dr. Elyce Cardonick, a perinatologist, was a research fellow at Cooper University Hospital in Camden, N.J., she met with a pregnant patient who had been told by her oncologist to terminate after learning she had Hodgkin’s disease. “She was afraid not to be treated for cancer, but she was afraid to expose her fetus to drugs,” Cardonick recalled when I spoke to her recently. It was perhaps the ultimate maternal conflict: choosing between the biological imperatives for self-preservation and procreation.

“We had to figure out what we could do to protect the fetus, but also what to do to protect the mother so that that baby had one,” Cardonick said. She did some research and found that pregnant patients had been treated with chemotherapy in Mexico, with what appeared to be remarkable success. In 1973, while still a resident, Dr. Agustin Avilés, a senior researcher at the Instituto Mexicano del Seguro Social in Mexico City, saw his first pregnant patient with acute leukemia. This woman became the impetus for Avilés’s groundbreaking study on the effects of chemo while pregnant, the first of 84 patients who received chemotherapy during pregnancy between 1973 and 2003, 58 of them during the first trimester. For most, termination wasn’t an option. Up until recently, medical abortions were rarely permitted in Mexico. Delaying treatment wasn’t viable, either. All 84 had acute leukemia, advanced Hodgkin’s or malignant lymphoma. Forestalling chemotherapy for even a few days could cost both mother and fetus their lives.

Google is again visiting the health spa, this time for a make-over for its mechanism for judging ad quality.

Google is again visiting the health spa, this time for a make-over for its mechanism for judging ad quality.

This critical measurement is the tool which deciphers which ads should be placed next to which search results.

As it stands, the system uses an auction system to determine which ads to place next to search results, Google rates these ads on how much they pay, the click-through rate and more recently how quickly the advertisers page loads as well as using a static measurement of value in evaluating whether to display an advertiser’s ad for a specific keyword.

The new system, announced by Google this week, will involve ad quality being judged at the time a user makes a search and will be tested on a small set of users before trying it with the majority.

Google said on its AdWords blog “We are replacing our static per-keyword Quality Scores with a system that will evaluate an ad’s quality each time it matches a search query. This way, AdWords will use the most accurate, specific, and up-to-date performance information when determining whether an ad should be displayed.”

The search engine giant also says, “We’re replacing minimum bids with a new, more meaningful metric: first page bids. First page bids are an estimate of the bid it would take for your ad to reach the first page of search results on Google Web search.”

Red Hat has launched a new engineering and support facility in Brisbane to sustain its expanding product line.

Red Hat has launched a new engineering and support facility in Brisbane to sustain its expanding product line.

The new facility replaces Red Hat’s existing Brisbane premises, which served as its Asia-Pacific engineering and support headquarters for the past nine years.

According to Paul Gampe, who is the software vendor’s vice president of Engineering Services and Operations, Red Hat’s regional engineering and support business has grown over the past six months.

“We have increased staff in both engineering and support, so we are launching this new facility to accommodate for this expansion and scale for future growth,” he told iTnews.

The new facility accommodates approximately 110 staff and has created ‘a number’ of new positions, Gampe said.

Boasting an area of almost 1,500 square metres spread across multiple storeys, the new facility is triple the size of its predecessor and now is Red Hat’s largest engineering centre in the Asia-Pacific region.

“Many technology companies have moved their development and support functions from Australia to China and India,” Gampe said, noting that Red Hat has facilities in all three countries.

“But for Red Hat, the growth of these two economies has contributed to the expansion of our operations in Australia … Brisbane is the regional headquarters for Engineering in Asia.”

“Our Brisbane centre provides service and support to customers around the globe, with Australian and New Zealand customers benefiting further because support is available in their time zone,” he said.

Red Hat’s Asia Pacific engineering and support staff conduct software research and development, product engineering, project management and software engineering activities.

This includes core graphics engineering, and Red Hat’s main translation team, which is responsible for making products available in 13 languages including German, French, Italian, Korean, Japanese, Mandarin, Cantonese and Indonesian.

Gampe highlighted staffing and scaling Red Hat’s support organisation inline with its business growth as two core focus areas of the new headquarters.

“A number of significant announcements were made at the Red Hat Summit in June, particularly around open virtualisation and Linux Automation strategies,” he said.

“Hand-in-hand with these announcements, we’ve increased the local investment in ‘behind-the-scenes’ engineering functions as part of our commitment to these initiatives.”

The new centre was officially opened yesterday afternoon by the Honourable Desley Boyle, Queensland Minister for Tourism, Regional Development and Industry.

According to Gampe, Red Hat’s Queensland location was chosen nine years ago because of ‘overwhelming’ state government support through a Queensland Government grant, and the quality of local engineering talent.

To support and sustain local talent, and contribute to the open source community, Red Hat’s Brisbane engineering centre will drive several initiatives promoting open source innovation and collaboration.

This includes Red Hat’s ongoing sponsorship of Honours research students at the Queensland University of Technology (QUT) and a research collaboration with QUT that will investigate open source localisation.

By Liz Tay