The RM series Transformer Core designed for use in high Q, high stability filters inductors. Its shape allows economic utilization of surface area on the PCB. The range is standardized in IEC 431 and is available worldwide from many suppliers. The sizes are based on the standard PCB grid distance. RM 5, for instance, fits on a board space of 5 x 5 modules of 2.5mm grid. Coil formers and clips were optimized for automated winding and mounting. The slots provide sufficient space for leads of windings. Magnetic shielding is not as good as with P-core, but still effective. For applications other than filter inductors the centre hole in the RM core is not necessary. Inductance adjustment is generally not required. For wideband and power transformers core performance can be improved by using a solid centre pole. AL-values will be higher and less flux concentrations occur in the core because its cross section has become more uniform.
