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This instructable will guide you through the process of hacking a stock 2-3db Linksys 2.54 gHz antenna into a 7db omni.

Antenna specs were taken from:
http://martybugs.net/wireless/collinear.cgi

That website is a great resource for a variety of antenna and wireless projects. I highly recommend it :)

Please take a moment to review the picture notes, as I will be referring to various parts of the antenna during the instructable.

Step 1: Materials and Tools

Materials
  • 300 mm of Copper solid core wire, 2.5mm is ideal. (Most power cords have solid core wire in them. Try scavenging from there)
  • Solder
  • Shrink Tubing
  • A 250mm length of PVC pipe (ABS would work as well). I used 1/2 inch diameter, as it is cheap and gets the job done.
  • Two (2)  PVC end caps
  • Epoxy glue
  • A collinear antenna ( From a wireless router or WLAN card or dealextreme.com)
Tools
  • Two pairs of needle nose pliers
  • a hammer
  • Vice-grips
  • Bench Vise (optional, but so very handy)
  • Soldering Iron
  • Exacto-knife, or some sort of razor blade.
  • Heat Gun (or a lighter)
  • Wire Strippers
  • a piece of metal stock or a thick screw driver to use as a template for the antenna.

Step 2: Strip and Straighten Copper Wire

1) Grip one end of the solid core copper wire in the bench vise.
2) Strip the insulation off of the entire length of the wire, using wire strippers.
3) Grip the free end of the copper wire with the vice grips, and pull taught.
4) Using a hammer, tap the vice grips away from the bench vice. This will straighten out your wire nicely, with minimal fuss. As an aside, you can also do this with soft copper tubing. Be especially gentle with the tube, as you can stretch it out and change the inner and outer diameters.


Step 3: Make the Antenna

Antenna Dimensions

Element 1: 61mm (1/2 wavelength)
Element 2: 91.5 mm (3/4 wavelength)
Whip: 83mm (>3/4 wavelength)

Assembly Instructions
1) Measure and mark 61 mm from one end of the straightened wire. Accuracy counts here, so if you have a set of vernier calipers or a drafting ruler, use them.
2) Make a 90 degree bend in the wire, at the mark.
3) If you have a bench vise, grip your stock or screw driver vertically (as seen in the movie below. Make sure you tighten it up more than I did though! It is annoying when the stock moves around.)
4) Using the stock as a circular form, make a small tight loop in your wire. Be careful not to bend the rest of your wire during this process. The loop in the antenna should NOT be centered, it should be on a bias to your antenna. Also, keep your loops smaller than the internal diameter of your PVC. 
5) Bend the wire 90 degree's back, so that the antenna is straight.
6) Construct the second loop the exact same way as above, except you will measure 3/4 of a wavelength.
7) Trim the whip portion to length.
8) Congratulations, you have just made a 7db gain antenna!




Step 4: Make the Antenna Body Out of PVC


1) Measure the total length of your antenna, add about 20 mm to the length and then cut a piece of PVC to size.
2) Measure the diameter of the SMC swivel arm, and then drill a hole in the center of one of your PVC end caps. This will be where the PVC joins the old SMA connector. You want this to be a tight fit. 
3) Using a couple drops of crazy glue, gorilla glue, or epoxy, glue the end-cap to the SMA connector. Don't use too much, otherwise you'll end up getting glue into the swivel arm, which is NOT a good thing (I speak from experience)
3b) Be sure to leave plenty of clearance between the end cap and the swivel joint. You don't want them to interfere with each other.
3) At this point, make sure that your antenna will fit inside the PVC,  if it doesn't carefully reduce the size of the loops..

Step 5: Hack the Old Antenna.

We are going to be wrecking your old antenna. If you are unwilling to risk the antenna on your card, DO NOT PROCEED. You can find all sorts of cheap antenna's over at dealextreme.com i.e (http://www.dealextreme.com/p/2-4ghz-wifi-router-antenna-5223). You can buy many of them for about $2, so order a couple of those to experiment with.

If you are brave, please follow along.

1) Look closely at your old antenna. There should be a very faint divide where the upper portion of the plastic case connects to the base. Grab the base just below the divide, and flex the upper portion back and forth. You want to break the glue holding the two pieces together, but not the base. The antenna inside is soldered very delicately, so if you are too forceful you run the risk of pulling the wire right out of the SMA connector, which is NOT a good thing.
2) Every antenna is different, each manufacturer protects the antenna  in their own unique way. You need to examine the inside of the antenna and figure out the best way to remove it. I generally like to desolder the old antenna. This is the least destructive way.
3) Once you have the old antenna removed, measure a piece of shrink wrap that you can put over the new antenna where it joins the SMA swivel connector. Slide the shrink wrap onto the first element of your antenna.
4) Soldier the antenna to the piece of wire protruding from the old SMA connector.
5) Slide the shrink tube over your newly soldered joint, and apply heat. This step is optional, but I think it gives the joint a little bit more strength.
6) Assemble the antenna body by carefully sliding the length of PVC down the antenna. Snug it into the end-cap carefully. Try not to wiggle the antenna around to much, as your soldiered joint is quite delicate.
7) Add the other end-cap to your PVC pipe, and you are done.

Step 6: Finished Product.

1) Before using PVC cement to close the antenna up, make sure you test it!
2) This antenna has an omni-directional emission, which means it broadcasts in all directions.
3) You can make the antenna look more "official" by sanding it down, and then painting it matte black. (I couldn't be bothered)

<br>Boosting the signal with amplifiers adds noise to the signal. WiFi antenna amplifiers are receive only, making your WiFi into what I call a &quot;Reverse Alligator&quot; (all ears, no mouth). If they can't hear you..... <br><br>Getting a stronger signal by using a high gain antenna is much better, and cheaper. If it's directional, this further improves both transmit and receive while allowing us to reduce undesired interference by aiming.<br><br>I built the &quot;cookie can antenna&quot;, made from a Pepperidge Farn Pirouette cookie can. To increase gain, I used a 4&quot; to 6&quot; adaptor, into a 6&quot; to 12&quot; rectangular adaptor, and ball piened it into a more circular shape. I sanded off the paint, clamped it with a large hose clamp and the &quot;straight&quot; flange from the 4&quot;-6&quot; adaptor (to make a handle), and sweat soldered both unions. The gain of the single-cone version is spec'd around _18 dBi. I figure the total gain of mine is around +25 dB. I used a short pigtail to N connector, and from there, uber-rigid LMR400. This has only 6.6 dB loss per hundred feet. I have a 25 footer and 15 footer, both with male and female N connectors, so my loss figure for both cables is probably closer to 2 dB. I mount it on a 20 foot mast, and turn it by hand.<br><br><br>
the length of the whip states it should be greater then 3/4 wavelength, but the length mentioned is less the 3/4 (since 3/4 is 91.5mm and the whip is only 83)<br><br>Is the measurement correct? Or should it be longer?<br><br>Thanks!
It was an error on the sign, sorry. it should be &lt;3/4<br>
COOL INSTRUCTABLE, WHAT IS THE NET GAIN IN WIFI AREA?
It really depends on what you mean by your question. If you are speaking in pure dB, then you can expect anywhere from 3-5dB gain over a stock antenna. If you are speaking in terms of physical area increased, I am not sure. The variables that affect RF broadcast are different at each location :)
is the pvc necessary or can the wire be antenna be left naked?
The wire CAN be left naked, but it is a rather delicate affair. I would strong encourage you to protect it with pvc or some other microwave transparent material. Also, if the bare antenna touches a metal object you risk grounding it, which could fry your radio transmitter. Alternatively, you could leave the wire insulation on. If RF can get through a wall, it can get through 0.5mm of insulation.

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