| 摘要 |
The interior surface of the horn is grooved with a uniform spiral pattern. The horn is made of a specified alloy, and after being formed by a molding technique, is internally coated with gold, e.g. by electroplating. The aerial consists of a horn (3) provided with an internal spiral groove (7) of constant step width, and comprises a shell made of an alloy of bismuth, lead and tin. Internal surfaces of the horn may be coated with gold. The horn may be made by using a mold, within which is placed a former which has a male imprint of the spiral. Molten material is poured into the mold and is then cooled. The mold and the horn are separated by plunging firstly into liquid nitrogen, and secondly into warm water. The gold coating may then be applied by electrolysis. Independent claims are included for a method of manufacturing the horn, and a molding former.
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