The J pole antenna
The j-pole antenna is a very useful antenna in situations where a DC ground and very little gain is required. The reason that I like the antenna is that it is simple to build, sturdy, and very easy to tune. A few things should be done though in order to prolong the life of the antenna.
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1. Clean all copper fittings well in order to insure a solid mechanical and electrical connection. A poor connection can mean that the antenna will "self-destruct" if it is put out in the weather and wind.
2. Use a stranded wire to connect the center pin to the shorter leg on antenna. I have used solid wire in this area and after a short amount of time the soldered joint will cause the the wire to break from the constant flexing of the pipe in the wind. The stranded wire will flex a slight bit so that it will not just break.
3. Solder and bolt the coax connector to the antenna. Both of these joints will work together to held insure a strong mechanical and electrical connection. Do not use a Radio Shack brand SO-239 connect as they are basically junk. The center insulative material will not withstand the temperature in the outside and will degrade rapidly. Tin an Ampenol brand connect with solder and then tin the pipe. After this has been done, bolt the connector with the tinned pieces facing each other and then warm the connector with a small torch. After the solder has set, it will be rock solid. 4. Don't skimp on cost as I have on some antennas, buy stainless steel hardware to bolt the antenna down. If you ever have to move the antenna or retune the antenna you will thank me for this hint.
5. Cap the pipes and paint the entire antenna. Painting the antenna with a NONMETALLIC PAINT will ensure that the antenna will last for years to come. Make sure to drill a small drain hole in the bottom leg of the antenna so that any condensation can drain out.
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The Yagi
The yagi also presents many mechanical as well as electrical concerns. Special care should be taken in acquiring insulative material and tubing for the antenna.
1. Use stainless steel hardware on the entire antenna whenever possible. Buy quality materials and the antenna will last.
2. Use properly sized element material. I prefer to build my 2 meter antennas out of old television antennas. The nontubular shape helps to drain away water easily and is very easy to cut with a a pair or tin snips. I also use square aluminum tubing on my antennas since it what is available and is easy to drill and setup with mounting hardware. Round tubing is nice, but without a good machine shop or a lot of patience this part might end your yagi building fun for good.
3. Clean and debur all elements and tubing when you are done. This may seem like a minor part of the building process, but it will prevent scratches and bruises if the antenna pokes you during the installation.
4. Over build the antenna. This is one thing that I can not stress enough. As an engineering student, one thing I have learned about is safety factors and making sure a product will last when it is put out in the world. 5. Make sure all bolts and other fasteners are tight when the antenna is installed. Either double nut the bolts or use a liquid holding materials such as Lock-TiteTM to insure that the vibrations caused by the wind will not loosen the fasteners.
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Quads
The quad is a very mechanically challenging antenna. Its many parts can cause mechanical failure if they are not properly manufactured and installed. Extra time should be taken in the preparation and installation of the antenna. 1. Use a material such as fiberglass or wood as the spacers. Fiberglass is the preferred material since it will flex with the wind and ice loading and is weather resistant. Wood dowels can be used on small 2 meter and 440 MHz antennas if they are treated with a wood protectant such as varnish or polyurethane. 2. When choosing boom material, make sure that it will be able to handle the stress of being torqued severely when strong winds move in [email protected]
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