Editing Medium wave (section)

==Antennas==
[[Image:Wire T antenna station WBZ 1925.jpg|thumb|Multiwire [[T antenna]] of radio station WBZ, Massachusetts, USA, 1925.  T antennas were the first antennas used for medium wave broadcasting, and are still used at lower power.]] 
For broadcasting, [[mast radiator]]s are the most common type of antenna used, consisting of a steel lattice [[guyed mast]] in which the mast structure itself is used as the antenna. Stations broadcasting with low power can use masts with heights of a quarter-[[wavelength]] (about 310 millivolts per meter using one kilowatt at one kilometre) to 5/8 wavelength (225 electrical degrees; about 440 millivolts per meter using one kilowatt at one kilometre), while high power stations mostly use half-wavelength to 5/9 wavelength. The usage of masts taller than 5/9 wavelength (200 electrical degrees; about 410 millivolts per meter using one kilowatt at one kilometre) with high power gives a poor vertical radiation pattern, and 195 electrical degrees (about 400 millivolts per meter using one kilowatt at one kilometre) is generally considered ideal in these cases. Mast antennas are usually series-excited (base driven); the feedline is attached to the mast at the base. The base of the antenna is at high electrical potential and must be supported on a ceramic [[electrical insulator|insulator]] to isolate it from the ground. Shunt-excited masts, in which the base of the mast is at a [[node (physics)|node]] of the standing wave at ground potential and so does not need to be insulated from the ground, have fallen into disuse, except in cases of exceptionally high power, 1 MW or more, where series excitation might be impractical.  If grounded masts or towers are required, [[cage aerial|cage]] or long-wire aerials are used. Another possibility consists of feeding the mast or the tower by cables running from the tuning unit to the guys or crossbars at a certain height.

Directional aerials consist of [[tower array|multiple masts]], which need not to be of the same height. It is also possible to realize directional aerials for mediumwave with cage aerials where some parts of the cage are fed with a certain phase difference.

For medium-wave (AM) broadcasting, quarter-wave masts are between {{convert|153|ft|m}} and {{convert|463|ft|m}} high, depending on the frequency.  Because such tall masts can be costly and uneconomic, other types of antennas are often used, which employ capacitive top-loading ([[electrical lengthening]]) to achieve equivalent signal strength with vertical masts shorter than a quarter wavelength.<ref>Weeks, W.L 1968, ''Antenna Engineering'', McGraw Hill Book Company, Section 2.6</ref> A "top hat" of radial wires is occasionally added to the top of mast radiators, to allow the mast to be made shorter.  For local broadcast stations and amateur stations of under 5&nbsp;kW, [[T-antenna|T- and L-antennas]] are often used, which consist of one or more horizontal wires suspended between two masts, attached to a vertical radiator wire.  A popular choice for lower-powered stations is the [[umbrella antenna]], which needs only one mast one-tenth wavelength or less in height.  This antenna uses a single mast insulated from ground and fed at the lower end against ground.  At the top of the mast, radial top-load wires are connected (usually about six) which slope downwards at an angle of 40–45 degrees as far as about one-third of the total height, where they are terminated in insulators and thence outwards to [[Earth anchor|ground anchors]].  Thus the umbrella antenna uses the guy wires as the top-load part of the antenna.  In all these antennas the smaller [[radiation resistance]] of the short radiator is increased by the [[capacitance]] added by the wires attached to the top of the antenna.

In some rare cases [[dipole antenna]]s are used, which are slung between two masts or towers. Such antennas are intended to radiate a [[skywave]]. The medium-wave transmitter at [[Transmitter Berlin-Britz|Berlin-Britz]] for transmitting RIAS used a cross dipole mounted on five 30.5-metre-high guyed masts to transmit the skywave to the ionosphere at nighttime.

===Receiving antennas===
[[Image:Ferritantenne 2.jpg|thumb|Typical ferrite rod antenna used in AM radio receivers]]
Because at these frequencies atmospheric noise is far above the receiver [[signal-to-noise ratio]], inefficient antennas much smaller than a wavelength can be used for receiving.  For reception at frequencies below 1.6&nbsp;MHz, which includes long and medium waves, [[loop antenna]]s are popular because of their ability to reject locally generated noise.  By far the most common antenna for broadcast reception is the [[Ferrite rod|ferrite-rod antenna]], also known as a loopstick antenna.  The high permeability ferrite core allows it to be compact enough to be enclosed inside the radio's case and still have adequate sensitivity.
For weak signal reception or to discriminate between different signals sharing a common frequency directional antennas are used. For best signal-to-noise ratio these are best located outdoors away from sources of electrical interference. Examples of such medium wave antennas<ref>{{Cite web|title=4: MW Aerials – Antennas – Medium Wave Circle|url=https://mwcircle.org/4-mw-aerials-antennas/|access-date=2021-11-28|language=en-GB}}</ref> include broadband untuned loops, elongated terminated loops, wave antennas (e.g. the [[Beverage antenna]]) and the ferrite sleeve loop antenna.