in size and frequency of operation: signal transformers, which are of small size and higher frequencies, and power transformers, which are of large size and lower frequencies. Cores can also be classified by shape, such as toroidal cores, shell cores or cylindrical cores. The ferrite cores used for power transformers work in the low frequency range (1 to 200 kHz usually) and are fairly large in size, can be toroidal, shell, or shaped like the letters ‘C’, ‘D’, or ‘E’. They are useful in all kinds of electronic switching devices – especially power supplies from 1 Watt to 1000 Watts maximum, since more powerful applications are usually out of range of ferritic single core and require grain oriented lamination cores. The ferrite cores used for signals have a range of applications from 1 kHz to many MHz, perhaps as much as 300 MHz, and have found their main application in electronics, such as in AM radios and RFID tags. Ferrite rod aerial Ferrite rod aerials (or antennas) are a type of small magnetic loop (SML) antenna very common in AM radio broadcast band transistor radios, although they began to be used in vacuum tube ("valve") radios in the 1950s. They are also useful in very low frequency (VLF) receivers, and can sometimes give good results over most of the shortwave frequencies (assuming a suitable ferrite is used). They consist of a coil of wire wound around a ferrite rod core (usually several inches longer than the coil, but sometimes over 3 feet long). This core effectively ‘concentrates’ the magnetic field of the radio waves to give a stronger signal than could be obtained by an air core loop antenna of comparable size, although still not as strong as the signal that could be obtained with a good outdoor wire aerial. Other names include loopstick antenna, ferrod, and ferrite-rod antenna. "Ferroceptor" is an older alternative name for a ferrite rod aerial, particularly used by Philips where the ferrite core would be called a "Ferroxcube" rod (a brand name acquired by Yageo from Philips in the year 2000). The short terms ferrite rod or ‘loop-stick’ sometimes refers to the coil-plus-ferrite combination that takes the place of both an external antenna and the radio's first tuned circuit, or just the ferrite core itself (the cylindrical rod or flat ferrite slab). See also Balun Ferrite bead Ferrite (magnet) Ferrite (iron) Magnetic core Toroidal inductors