English: An early rhombic antenna in 1937 in Dixon, California, USA. It was built by the American Telephone and Telegraph Co. for long distance telephone service to the Far East via shortwave radio. It communicates with a station in Shanghai, China, 6100 miles away. The antenna consists of two parallel wires strung in the shape of a rhombus from telephone poles. It is fed from the near end and terminated by a transmission line at the far end.
This 1937 issue of Short-Wave and Television magazine would have the copyright renewed in 1965. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. Search of the Renewals for Periodicals for 1964, 1965, and 1966 show no renewal entries for Short-Wave and Television. Therefore the copyright was not renewed and it is in the public domain.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.