Radio-frequency losses of yba₂cu₃o_7-δcomposite superconductors

YBa₂Cu₃O_{7- delta}multi-crystalline ceramics were shaped into one-turn coils. The RF performance of the coils was evaluated by measuring the Q-value at 77 K from 1.3 to 270 MHz and comparing it with that of a Cu coil of the same geometry. The coils were also tested as NMR detection coils. In a poorly magnetically shielded environment the multicrystalline YBa₂Cu₃O_{7- delta}performed less well than Cu in the frequency range studied. Q was significantly lowered by applying a magnetic field. The temperature dependence of the Q-value also was measured at 100 MHz, from 77 K to well above the superconducting phase transition temperature.