Materials for the manufacture of antennas. Scheme, description

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Materials for the manufacture of antennas. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Television antennas

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Separately, it is necessary to dwell on the materials that are used in the manufacture of the antenna. Antenna elements can be made of tubes, rods, strips or corners of any metal. In accordance with the surface effect, high-frequency currents flow exclusively along the surface of the metal, so a thin-walled tube or a solid rod of the same diameter is exactly the same in its properties.

Typically, television antennas are made of aluminum or its alloys. This is due to the fact that the antenna from such tubes is quite strong and light. However, the electrical properties of aluminum antennas are not high enough due to the fact that poor contacts are often formed at the junctions of antenna elements, caused by an oxide film covering the surface of aluminum alloys. This can lead to antenna failure over time.

It gets even worse when, when assembling the antenna, elements or coupling bolts from different metals are used. In this case, due to the contact potential difference, a galvanic couple arises, destroying the metal at the junction. Therefore, aluminum antennas are best connected using gas welding or, in extreme cases, using aluminum tie bolts, nuts and washers. Before assembling, it is useful to clean the elements at the joints well with a file and generously lubricate with technical petroleum jelly to prevent the formation of an oxide film.

In principle, the antenna can be made of any metal; copper, brass, bronze, steel or stainless steel. Compared to aluminum antennas, such antennas will of course be significantly heavier. In all cases, it is desirable to connect the antenna elements in such a way as to exclude the possibility of poor contacts due to corrosion or destruction from electrolysis. To do this, all connections are best welded or soldered. In this case, the antenna elements can also be made of different metals. If steel elements were used and soldered using an acid flux, the soldering points must be thoroughly washed with hot water to remove its residues, otherwise the flux residues will lead to severe corrosion of the metal for a short time.

It should be remembered that soldering serves only to ensure good electrical contact. Soldering with tin solders does not withstand mechanical loads. Therefore, it is necessary to ensure the strength of the connections by other methods (rivets, bolts, etc.), and after assembly, these connections should be soldered. The exception is brazing, which has sufficient strength. To avoid corrosion, the antenna after complete assembly and soldering of the feeder with the matching device to it is thoroughly cleaned of oxides and well painted over in several layers with oil or nitro paint. Synthetic car enamels can also be used. These dyes are good dielectrics and do not affect the operation of the antenna at all. It is undesirable to use aluminum paints, since they have a finite resistance value.

The cable connection points to the antenna elements must be sealed to prevent moisture ingress. The best sealing is achieved by using plasticized epoxy resin. Such a resin in the form of an epoxy adhesive of the EDP brand is available for sale in household goods stores. The place to be sealed is superimposed on a piece of plasticine, a recess of the appropriate shape is made in it and filled with resin. After it hardens, the plasticine is removed, and the surface of the resin is processed with a file to give it an even shape. For a good fit of the resin to the metal, it must first be degreased with acetone.

Based on the book by V.A. Nikitin How to achieve good TV performance; Publication: cxem.net

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