Antennas
Transmitting antennas commonly used on this band include monopole mast radiators, top-loaded wire monopole antennas such as the inverted-L and T antennas, and wire dipole antennas. Ground wave propagation, the most widely-used type at these frequencies, requires vertically polarized antennas like monopoles. Receiving antennas are usually outdoor random wire antennas or ferrite loop antennas.
Even a quarter-wave antenna at MF can be physically large (25 to 250 metres (82 to 820 ft), depending for which part of the band), and a half-wave dipole will be twice that size. Given the requirements for gaining an adequate height and for a good earth, this can make demands on establishing an efficient antenna system for an MF transmitter.
On the other hand, loop antennas can be physically much smaller than the wavelength they receive, so ferrite is very efficient at MF and so a compact and efficient reception antenna can be made from a ferrite rod with a coil of fine wire wound around it. These are common in AM radios and are also used in portable radio direction finder (RDF) receivers. The reception pattern of ferrite rod antennas has sharp nulls along the axis of the rod, so that reception is at its best when the rod is at right angles to the transmitter, but fades to nothing when the rod points exactly at the transmitter.
Read more about this topic: Medium Frequency