Introduction: The Making of a Beast: Part Two, the BiQuad Antenna

By diverseworx

So now that basics are done on the WRT54G; now it is time to create the antenna I want to use.  I have a small line of site path though some trees, to the area I want to broadcast to.  So I wanted to use a Bi-quad with a parabolic reflector.  I acquired all the parts for free, out of metal dumpster, and other scrap sources.

This instrucables was going to also include some more WRT mods; however, while de-soldering the RAM chip I damage a part of the board, so I am waiting on parts.  So now there will be a Part Three :) 

This will only discuss the making of the antenna.  One could use any antenna element of choice; cantenna, dipole, or a bi-quad.  This instructable is more about getting the juices flowing, to inspire some one to create better.  And part three will be about how it all comes together.

The Prequel

Step 1: The Parts.

For the constuction of a Bi-Quad, the following parts are needed:

# A small section of 3/4 (or smaller) copper pipe, about  8". 

# A piece of square, flat, copper, if using a parabolic dish the dimesions are 110x110mm, without 123x123mm is best.  Copper clad PCB board works, I chose just a sheet of copper I found.  You can use anything coductive, I use copper because the ease of workability, and low loss; however,  you can use any metal for any part of the project.

#Coax, a LMR-195 if < 5' to the transceiver, LMR-400 if > 5',  RG-58 will work if the section is short. 

That's it.

If making a parabolic dish, one will need a dish :)  Recycled one if possible.  There is a lot of science about which size dish to use for 2.4GHz.  Personally, this is about a cheap hack job, and I can get a lot more coverage with a old TV dish (direct tv style). 

Skills & Tools needed:

# Soldering skills is a must, I used a propane torch for most of this project.  A high watt soldering iron can, and has, worked.

#  Hack saw, file, tin snips, wire strippers, a crescent wrench, flashlight.

# Ingenuity; each person that tries to match this will run into their own problems, wants, desires; we are here to help; yet, a level of McGyver like skills is a plus.  I made this using no money, I could improve greatly on it If I choose.  Make it your own.

And last but not least, educate ourselves :)  I put some great links through the steps.  If you are expert or novice, it helps knowing a little.

http://www.trevormarshall.com/biquad.htm

http://en.wikipedia.org/wiki/Parabolic_antenna

http://en.wikipedia.org/wiki/Antenna_(radio)

Step 2: Affixing the Reflector.


First thing we want to do is, make a square.  If making side flaps, make it 30mm longer on one side, so 123x153mm or 110x140mm.  I did not do this, it would impact a longer range signal.  I made my flaps only 10mm

Once square, draw line corner to corner (of the square) to determine center.  Find the out diameter of the pipe you are using, some of you might solder in a bulk head jack instead of pipe.  Either or, drill a hole to fit.

Clean up any burrs and apply flux. 

Next clean your pipe :) Polish until shiny, then flux and slip it through the hole. 

To solder using a torch: Capillary action is used to make a good joint.  If you have never soldered with torch; How to Sweat (solder).  It is best to have the pipe in a vice and the sheet flat on the jaws of the vice.  There will be warping, but it is another reason I like copper, it is easily taken care of later.

Heat up the sheet, as soon as it is hot enough, pull the flame back and lay in the solder, it should flow right into the joint, via capillary action :)  Let it sit for a while, it is going to be hot.  If using a soldering iron, take your time you will get it eventually, a 60w or 120w might do the trick.  I would recommend learning to sweat solder.  If using a copper clad board maybe not.  A warning, each type of metal is different, do your research before you solder on it.  I do not want some one taking a torch to a piece of magnesium.  Another reason to use copper. :)

Step 3: Finish Up on the Reflector

If we have not cut to size, now is a good time, mark and use straight tin snips to make your cut.  Another method is a sharp chisel and a hammer, on a wood surface. 

After it is the size you want, making it straight is as easy as a hammer and a block of wood.  I use an anvil as a backing, but anything smooth and tough will do.  Give some good whacks and the copper will look as good as new.

Now I will cut the excess of pipe.  The element needs to be between 15-17mm from the reflector. This will make for the lowest SWR, which is important.  Since most of us do not have SWR meters for 2.4GHz, we can only take information from other and do our best.

(I have thought of ways to make this part adjustable, and would love to see some one do it.  A hollow piece of threaded stock would work great.  The SWRs could be tuned, then.)

I cut the back pipe enough to mount on my dish, how much to leave is up to the builder.  After that, file down 1/2the diameter of the pipe, down about 3mm.  So now one side of the pipe should be 15mm and the other 12mm.  That is it for the reflector; the bends are optional, but they cut back on rear and side lobe radiation and are recommend when using a dish.

Step 4: Mounting on the Dish.

My dish did not come with the LNB, and I am kind of glad it do not.  What one wants is a way to adjust x, y, and z axis and the polarization.  I used a piece of power strut (useful stuff, search superstrut), and two pieces of scrap metal, a piece of PVC and a hose clamp.  The bolt on the strut, lets me turn the x and forward and back on the z. The bend in the metal can allow me to move on the y.

This step is really up to the builder, I am just giving a basic idea how it can be done.  It could be a lot more functional then this. and could even be servo driven.

Step 5: Tuning


Since I painted it white, it is reflective.  If you don't want it white, cover it in tin foil.  Or use algebra to figure out the right spot, search here.  If you are lucky, the dish you will be using will have a LNB and you can go from there.

I used a flash light pointed at the angle I wanted.  Then attached a piece of paper on the reflector and tried to get it dead on.  It gave me about a 2" circle of light to work with.  Now think there is a lot going on here, not only is this dish designed for a different use, but also a different antenna.  LNB are mostly cantenna in design, so I brought the bi-quad back a bit farther.

Step 6: The Element.


Be patient, cut a piece of wire, I used a 14g solid copper which is 1.6mm.  In researching this, I found size matters ;) 1.2mm is preferable.  The thicker the wire the larger the bandwidth of the antenna.  First straighten then cut it exactly 244mm.  Measure and mark it at 122mm, make a 90 degree bend. From the center of the wire measure 30.5-.75mm mark and bend.  Do this to each side until you get what is pictured. Two quad elements.  Each length is a 1/4 wave of 2.4GHz.  It a good thing to understand this Hertz thing so try here.

As soon as the perfect element is shaped solder the open ends on the high part of the pipe on the reflector.  Measure, then measure again.  Go around the entire outside edge of the element making sure it is off the reflector 15-17mm.  Mine was 15.5mm all around after a couple tweaks.

Slip in your coax and solder the core to the center and the shielding to the inside of the pipe. 

Done deal.

Step 7: Finish Up.


I coated everything copper with electrical anti-corrosion spray, then painted with light coat of not conductive paint.  I am hoping it does not mess with the signal much.  I do not think it will.  I have made antennas for years and painted a bunch of them and never lost much db off the top.  So any advice in that department, I would gladly accept. :)  I made a sticker to :)

Next are some lighting mods, and some more work on the router and setup.  Till part three, Thanx