This type of antenna can be easily built. Exact size and construction are not very critical. They almost always work. Their typical gain is 8-10 dBi, which is pretty good. They look like this:
The antenna is built on a piece of Printed Circuit board of 10 by 15 centimeters. Right in the middle of this we drill a hole that is the size of the diameter of a female N-connector chassis mount.
The female N-connector chassis mount:
The heart of the antenna is a piece of bended brass or copper wire
The diameter of the brass or copper wire should be about 1.5 millimeter. The inner sides of the squares (quads) must have a size of about 28 mm. A tolerance of a millimeter or so is allowed.
The following link shows a drawing with an overview of various measures: wleiden.webweaving.org/bq.pdf (Text is in dutch)
The bending of the wire is the hardest. It is important to have the final bended wire in one plane. This can be checked by laying the copper product on a flat surface. All the copper should be stable and flat on the surface. It should not wobble.
Marten constructed a special little tool too make the bending easier.
But with a pair of tongs it can be done too.
After the copper has been bended right it is soldered on the chassis mount:
The distance between the PCB and the copper wire must be about 15-17 millimeters. With the chassis mount shown here this distance can be adjusted. In other types it must be soldered rather precisely.
The two end points of the bended wire are connected with solder and connected to the chassis mount. Right at other side of the copper - where the wire makes an inside angle - is the other connection point with the chassis mount. This can be seen on the next picture:
There is no plus or minus. It does not matter what is connented to the middle of the chasis mount. The soldering can best be done with a solder pistol or a pretty powerfull soldering bolt (50-100 VA). My 25 VA soldering bolt did not do the job. On the other hand care should be taken not to make the chassis mount too hot, the kernel can melt and be damaged
The result should now be as already shown above:
The antenna is now ready for use.
It is advised to put the result in a box of some kind, especially when it's used in outside weather
conditions. Microwave boxes as used by take away food stores are fine.
The same is true for plastic boxes for video tapes, these are just the right size.
Boxes should not contain any metal or absorb water.
This can be tested by laying them in a microwave for a minute or so.
If the do not become warm it's ok.
If they do get hot, considerable loss in gain may be the result.
Good luck.
Tom Duijkers
Leiden, The Netherlands. mail