As medium waves ( MW MF ENGL. Medium frequency or on receivers often with AM for " amplitude modulation " hereinafter) is defined as electromagnetic waves in the range of 300 kHz (1,000 m wavelength) to 3000 kHz ( 100 m).
Due to their good reflective properties of the ionosphere, the center shaft is particularly suitable for long-distance transmission and is used by broadcasting, by radio amateurs (160 meter band ) and in the marine radio. For historical reasons, the amplitude modulation is used because AM with the simplest of means (crystal receiver) can demodulate, which was crucial in the early years of broadcasting.
From a medium-wave transmitter both a ground wave and a sky wave can be radiated ( depending on the antenna shape). The ground wave propagates along the earth's surface and has, depending on the used frequency, a range of up to 300 km to the transmission tower. When transmitting antennas today come mostly self-radiating masts and T antennas are used, but also crossed dipoles with vertical radiation. Rare grounded towers, suspended on poles Vertical traps or long wire antennas are used.
The space wave plays an important role in remote reception. This is emitted into the atmosphere, and is reflected off the ionosphere back to the surface. In the daytime, the ionosphere attenuates the medium wave signals, because it contains a lot of unbound electrons. At night, when the damping is weaker by the D - region, the range increases to more than a thousand kilometers. Therefore, at night, a larger number are received at broadcast stations than during the day. So even medium wave stations can be received from the American continent in Europe during the night hours.
If space and receive bump together, then there will be interference, the Nahschwund.
The commonly used for radio broadcasts around the center shaft is between 525 kHz and 1705 kHz, which is the total extension of all the world's allocated bands by GE75 ( Geneva Conference ), RJ81 and RJ88 (ITU- agreements ), which differ slightly from each other. Lowest ever in Europe frequency used was that of the BR to 522 kHz ( here due to one of many special assignments that were issued only for very small transmitter power), the highest frequency in Europe was used until 1 July 2012 by Vatican Radio 1611 kHz.
Use of medium wave in Europe
Due to the shutdown of many powerful radio transmitters in the medium wave range of a few radio stations can be received in Europe than in the mid 1980s in 2010.
Analog video recorders which operate according to the color-under process, save the color signal of the video image in the medium- wave at 600-1000 kilohertz. According to this method work almost all analog home video recorder such as VHS and Video8.