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This page details the construction of an easy-to-make collinear 360 degrees omni-directional, vertically polarised, antenna for 802.11b/g wireless networking. The antenna is very robust and compact, and has a gain of approximately 5-6dBi.
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Background
Various websites detail the construction of a collinear antenna suitable for 2.4GHz wireless networking, including and guerrilla.net (no longer available, but mirrored ). However, these antennas are quite complex to build, being made up of numerous short lengths of coax which must be accurately cut to length. You also need to know the velocity factor of the coax that is being used, as most of the measurements are based on it.
A of the coax collinear is constructed from brass rod and brass tubing, but is still just as fiddly to construct.
Some time ago, I made an 8-element coax collinear, using the instructions. confirmed the gain was approximately 8dBi.
However, it took many hours to construct, and the antenna has very little physical strength. I resorted to cable-tying a length of dowel to the coax, and then encasing it all inside some 25mm electrical conduit.
I was particularly intrigued when a friend pointed out a much simpler collinear, consisting of just a length of copper wire appropriately bent, as detailed , with a claimed gain of about 6dBi.
This version provides a number of benefits over the coax construction, requiring far less effort to construct, and providing a smaller and more robust antenna.
While the 6dBi gain is less than that of an 8 element coax collinear, the gain could be improved by increasing the number of elements. Doubling the number of elements will increase the gain by 3dBi, ie, double the gain.
Parts Required
The materials required:
· approx 300mm 2.5mm2 copper wire
· panel-mount female N-connector
· 250mm length of 20mm light-duty electrical conduit
· 2 end-caps to suit 20mm conduit
and optionally, for mounting of the completed collinear antenna:
· 2 clamps to suit 20mm conduit
or
· metal bracket
I used a length of copper wire from some scraps of 2.5mm2 electrical cable I had lying around. This cable has a diameter of approximately 1.6mm, and is flexible enough to bend into the required shape without too much effort or specialised tools.
2.5mm2 3-core electrical cable
A panel-mount female N-type connector is also required, to allow the antenna to be connected to a wireless device. Note that other connectors (ie, TNC, SMA, etc) can also be used, depending on the connectors on your pigtails.
I used a panel-mount female N-type connector, as shown in the photos below.
panel-mount...
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