Atmospheric radio ducts can trap VHF/UHF radio waves and propagate them over long distances. 284.4625 MHz Japanese radio wave signal measurements show that the radio waves are propagated to Korea coastal regions when ground temperatures exceed 10C. This paper discusses the reasons for the existence of this critical temperature threshold.

A sputtering system using dc hollow cathode discharge was developed for the propose of high Tc superconducting devices. Using this system, as-grown superconducting thin films of YBCO have been formed on MgO and SrTiO3 substrates. Influence of the sputtering conditions such as the substrate temperature and discharge gas pressure on the Tc and lattice parameter was investigated. It was found that superconducting films on MgO with Tczero higher than 87 K ere routinely obtained at the pressure of 820 mTorr (5%O2) and substrate temperature of 700 during deposition. The a/b-axis and c-axis oriented YBCO-PBCO hetero-structures were also successfully formed on MgO and SrTiO3 substrates.