Editing Medium frequency (section)

==Antennas==
[[Image:Ferritantenne 2.jpg|thumb|Ferrite [[loop antenna|loopstick]] receiving antenna used in AM radios]] 
[[File:Amateur T cage antenna 2BML 1922.jpg|thumb|Cage [[T antenna]] used by amateur radio transmitter on 1.5 MHz. ]]

Transmitting antennas commonly used on this band include [[Monopole antenna|monopole]] [[mast radiator]]s, top-loaded wire monopole antennas such as the inverted-L and [[T antenna]]s, and wire [[dipole antenna]]s.    [[Ground wave]] propagation, the most widely used type at these frequencies, requires vertically polarized antennas like monopoles.

The most common transmitting antennas, monopoles of one-quarter to five-eighths wavelength, are physically large at these frequencies, {{convert|25|to|250|m|ft|0}} requiring a tall [[radio mast]].  Usually the metal mast itself is energized and used as the antenna, and is mounted on a large porcelain insulator to isolate it from the ground; this is called a ''[[mast radiator]]''.  The monopole antenna, particularly if [[electrical length|electrically short]] requires a good, low resistance Earth [[ground (electricity)|ground]] connection for efficiency since the ground resistance is in series with the antenna and consumes transmitter power.   Commercial radio stations use a ground system consisting of many copper cables, buried shallowly in the earth, radiating from the base of the antenna to a distance of about a quarter wavelength.  In areas of rocky or sandy soil where the ground conductivity is poor, above-ground [[counterpoise (ground system)|counterpoise]]s are sometimes used.

Lower power transmitters often use [[electrical length|electrically short]] quarter wave monopoles such as inverted-L or [[T antenna]]s, which are brought into resonance with a [[loading coil]] at their base.

Receiving antennas do not have to be as efficient as transmitting antennas since in this band the [[signal-to-noise ratio]] is determined by atmospheric noise.  The [[noise floor]] in the receiver is far below the noise in the signal, so antennas small in comparison to the wavelength, which are inefficient and produce low signal strength, can be used.  The weak signal from the antenna can be [[amplifier|amplified]] in the receiver without introducing significant noise.  The most common receiving antenna is the [[Ferrite (magnet)|ferrite]] [[loopstick antenna]] (also known as a ''[[ferrite rod]] aerial''), made from a ferrite rod with a coil of fine wire wound around it.  This antenna is small enough that it is usually enclosed inside the radio case.   In addition to their use in AM radios, ferrite antennas are also used in portable [[radio direction finder]] (RDF) receivers. The ferrite rod antenna has a [[dipole antenna|dipole]] [[Radiation pattern|reception pattern]] with sharp [[Null (physics)|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.  Other types of [[loop antenna]]s and [[random wire antenna]]s are also used.