802.11 WIFI ADAPTER RECEPTION

AMPLIFICATION UNIT RESEARCH

PROJECT

Fabius Watson

PROJECT GOAL

Overall Goal

Construct a device that increases wireless signal

gain by a minimum of 10 dBi.

Provide the device with simple functionality.

Incorporate a swivel mount for adjustability.

PARABOLLIC DISH APPROACH

Most WiFi Adapters are built for omnidirectional functionality.

Most users only connect to a single access point (EX: linksys) at a time.

The Devices omnidirectional functionality limits maximum gain.

A Parabollic Dish would reflect all captured signal toward the focal point of the dish, at which the adapter’s antenna would be located, maximizing signal gain from a single access point.

MATERIALS

External USB 802.11b/g/n Wireless LAN Adapter

USB 2.0 Extension Cable, 10 ft

Camera Tripod

Plywood

Duct Tape

Aluminum Foil

Poster Board

WHAT IS A PARABOLIC DISH?

A parabolic reflector (or dish or mirror) is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis. The parabolic reflector transforms an incoming plane wave traveling along the axis into a spherical wave converging toward the focus. Conversely, a spherical wave generated by a point source placed in the focus is transformed into a plane wave propagating as a collimated beam along the axis.

(Source A)

HOW DOES A PARABOLIC DISH WORK?

When EM waves arrive on parallel paths from a distance source and are reflected by a mirror or flat surface, the angle of the path leaving (angle of reflection) is the same as the angle of the path arriving (angle of incidence).

If the mirror is a flat surface, the two rays of light leave in parallel paths; however, if the mirror is curved, two parallel incident rays leave at different angles.

If the curve is parabolic (y = ax^2) then all the reflected rays meet at one point.

A dish is a parabola of rotation, a parabolic curve rotated around an axis which passes through the focus and the center of the curve.

(Source B)

PARABOLA WITH FOCUS AND ARBITRARY LINES

(Source A)

APERTURE

The aperture of an antenna is the area that

captures energy from a passing radio wave.

For a dish antenna, the aperture A would be the

area of the reflector as seen by a passing radio

wave:

A = πr2

Where r is the radius, half of the dish’s diameter.

(Source B)

GAIN

FOCAL LENGTH

CONSTRUCTION - PARABOLLIC DISH

In order to build my own parabolic dish I loosely

followed a guide found at www.instructables.com,

making slight improvises in terms of materials.

NOTE TO THE

AUDIENCE

All Slides Proceeding This Slide Are

Completely Impromptu

DISH FAIL

However, My Dish Construction Failed. =(

It was too heavy due to foil, glue, and duct tape

It’s weight caused a degradation in its stability,

giving it a flimsy form

TESTING THE DISH ANYWAY

Despite, my dish failing, I decided to test the dish anyways.

I was able to crudely test for an increase in gain using my IpodTouch and a tool called WiFiFoFum.

Calculating a focal length of 7.8 inches, and strategically placing my Ipod Touch at approximately this length at the center of the dish, I was able to get a maximum of a 20 dBi increase in gain

CONCLUSION

Although my design was plausible in theory, it was

flawed when physically applied.

Applied science is much more frustrating than Pure

science.

Things Fail.

FAIL CONT…

Another problem that I ran into is getting the wireless adapter to register on my computer.

The Wireless Adpater I attempted to use contained a Ralink rt3070 chipset.

Ralink fails at chipsets. The rt3070 chipset is the same exact chipset as the rt2860 with minor bug fixes.

I had to reconfigure the driver for the rt2860 so that it would register as the rt3070.

DRIVER WONT INSTALL

FINALLY

After 2 hours of CLI torture, I managed to get the

driver to install.

HOWEVER…

The Physical Adapter would not function at all.

After hitting up freenode/#sabayon for some help, I was able to determine the cause of the problem.

The USB Adapter was not receiving enough power to function properly due to:

The 1.82 m USB extension Cable (power is lost over the distance)

Front Panel USB port. A Root port is necessary for maximum power.

So after moving the USB to a root port & removing the USB adapter I was able to get the adapter to function properly.

Just one minor issue…

MORE FAIL*CRIES*

I need the adapter to work with the USB extension

cable.

Without the Extension cable, the adapter will never

reach the dish

WAVEGUIDE APPROACH

Speaking of the dish, I decided to scrap the dish

idea, as it utterly failed.

I decided to instead construct a model based on an

Waveguide Antenna.

CANTENNA

I recalled back to when I began this project and remembered a picture I had seen of similar projects. I turned out to be called a Cantenna

It involved the usage of a pringles can to reflect the wireless signal, and looked fairly simple to construct.

And so I decided I had nothing to lose and proclaimed (to myself) my refusal to ReInvent the wheel.

i buy teh pringles

PRINGLE FAIL

While the Dish, though crappy, boasted a max 20 dBi increase, the Pringles can, though cool looking and inventive, boasted a min 15 dBidecrease.

Turns out the inner coating of the pringles can, contrary to my previous belief, is NOT mettallic.

Waveguide functionality will NOT work. However if I had taken a Yagi-Uda approach (Microwave Resonance), It probably would have increased my gain by at least 10 dBi.

DO NOT believe everything you read on the internet.

FMJC: FULL METAL JACKET CANTENNA

Well, If Metal is the problem, I’ll simply a Full Metal

Can, rather than a cardboard pringles can.

I’m going to stick with the Cantenna design as it is

documented as having worked fairly well on several

different occasions.

The Tin Can Cantenna works fairly well in that I achieve

a 15 dBi increase.

The Downside of this is that the wireless adapter that I

originally intended to use has still failed to gain enough

power to constantly function correctly. (I did manage to

get it to register for a brief moment, but soon after it

died.) And the one I’ve been using for testing (Yes, I

dumped my Ipod touch) is half broken (What a surprise!

It sports a Ralink chipset as well!.)

Also the can is small, crude, ugly, and not what I was

going for.

NOW WHAT?

I’ve run out of time, and hereby proclaim this project:

WHAT DID I

This project wasn’t a complete lost, I learned as much doing this project as I did I most of my other classes.

I learned a ton about waves, antennae, parabolas, etc. That I didn’t know before, and probably would never have learned unless I did attempt this project or a project similar.

I learned to modify & compile drivers in Linux using C?

I learned that engineering consists of more than just math and physics. It also consists of trying, failing, and trying again.

I learned that Cantennas are completely Illegal. That’s right, after completing this project, I discovered that what I wa doing violated FCC guidelines any way, and carried a hefty fine.

Also, if it only took about 10,000 tries for Edison to perfect his light bulb, he must have been a genius.

NOT DONE YET

Despite the Law I plan to continue my research on Wireless

Adapter Reception Amplification Units

I may attempt to construct a model using a Satellite TV dish

and a BiQuad antenna. This model has reported achieving a

max 30 dBi increase.

I’m also thinking about an Umbrella Frame with a Wire Mesh.

Bigger aperture, more gain, remember?

I also plan on experimenting with Bluetooth and GPRS

WORKS CITED

(Source A) Chambers, Robert. "Parabolic

Reflector." Wikipedia, the Free Encyclopedia. Web.

16 July 2010.

<http://en.wikipedia.org/wiki/Parabolic_reflector>.

(Source B) "Web Site Of: W1GHZ (n1bwt)."

Welcome to QSL.NET :: Web Services for Ham

Radio Operators. Web. 16 July 2010.

<http://www.qsl.net/n1bwt/>.

WIFI IS SEXY