Very high frequency (VHF) is the radio frequency range from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF). The frequency allocation is done by ITU.

These names referring to high-end frequency usage originate from mid-20th century, when regular radio service used MF, Medium Frequencies, better known as "AM" in USA, below the HF. Currently VHF is at the low-end of practical frequency usage, new systems tending to use frequencies in SHF and EHF above the UHF range. See Radio spectrum for full picture.

Common uses for VHF are FM radio broadcast, television broadcast, land mobile stations (emergency, business, private use and military), long range data communication with radio modems, amateur radio, marine communications, air traffic control communications and air navigation systems (e.g. VOR, DME & ILS).

VHF propagation characteristics are ideal for short-distance terrestrial communication, with a range generally somewhat farther than line-of-sight from the transmitter (see formula below). Unlike high frequencies (HF), the ionosphere does not usually reflect VHF radio and thus transmissions are restricted to the local area (and don't interfere with transmissions thousands of kilometres away). VHF is also less affected by atmospheric noise and interference from electrical equipment than lower frequencies. Whilst it is more easily blocked by land features than HF and lower frequencies, it is less affected by buildings and other less substantial objects than UHF frequencies.

High frequency (HF) radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters (ten to one hundred metres). Frequencies immediately below HF are denoted Medium-frequency (MF), and the next higher frequencies are known as Very high frequency (VHF). The Shortwave range (2.310 - 25.820 MHz) used by international broadcasters is part of the HF frequency spectrum. In aviation virtually the entire spectrum (2 - 29.999 MHz) is used for HF communications.

The ionosphere often refracts HF radio waves quite well. This phenomenon is known as skywave propagation. Because of these characteristics this range is extensively used for medium and long range radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors:

These and other factors contribute, at each point in time for a given communication path, to a

The maximum usable frequency regularly drops below 10 MHz in darkness during the winter months, while in summer during daylight it can easily surpass 30 MHz. It depends on the angle of incidence of the waves; it is lowest when the waves are directed straight upwards, and is higher with less acute angles. This means that at longer distances, where the waves graze the ionosphere at a very blunt angle, the MUF may be much higher. The lowest usable frequency depends on the absorption in the lower layer of the ionosphere (the D-layer). This absorption is stronger at low frequencies and is also stronger with increased solar activity (for example in daylight); total absorption often occurs at frequencies below 5 MHz during daytime. The result of these two factors is that the usable spectrum shifts towards the lower frequencies and into the Medium Frequency (MF) range during winter nights, while on a day in full summer the higher frequencies tend to be more usable, often into the lower VHF range.^{[citation needed]}

Nikola Tesla (Serbian Cyrillic: Никола Тесла; 10 July 1856 – 7 January 1943) was a Serbian-American inventor, physicist, mechanical engineer, electrical engineer, and futurist. He was an important contributor to the use of commercial electricity, and is best known for developing the modern alternating current (AC) electrical supply system. His many revolutionary developments in the field of electromagnetism in the late 19th and early 20th centuries were based on the theories of electromagnetic technology discovered by Michael Faraday. Tesla's patents and theoretical work also formed the basis of wireless communication and the radio.

Born in the village of Smiljan (now part of Gospić, present day Croatia), Tesla was a subject of the Austrian Empire by birth and later became an American citizen. Because of his 1894 demonstration of short range wireless communication through radio and as the eventual victor in the "War of Currents", he was widely respected as one of the greatest electrical engineers who worked in America. He pioneered modern electrical engineering and many of his discoveries were of groundbreaking importance. In the United States during this time, Tesla's fame rivaled that of any other inventor or scientist in history or popular culture. Tesla demonstrated wireless energy transfer to power electronic devices in 1891, and aspired to intercontinental wireless transmission of industrial power in his unfinished Wardenclyffe Tower project.

The Lille metro (French: Métro de Lille) is a driverless metro in France. It was inaugurated on 25 April 1983 and was the first to use VAL (French: véhicule automatique léger, English: light automated vehicle) system.

The metro forms part of a multi-modal mode public transport system with buses and trams, operated under the Transpole brand and covering the Lille metropolitan area.

Construction started in 1978 and the first line was inaugurated on 25 April 1983 between 4 Cantons and République. On 2 May 1984 line 1 was completed (13.5 km long, 8.5 km underground), linking CHR B Calmette to 4 Cantons via Gare de Lille Flandres, with 18 stations. All stations have doors between the platform and the train.

Line 2 opened on 3 April 1989 and it reached CH Dron near the Belgian border on 27 October 2000. It is 32 km long with 43 stations.

Trains are 2 metres wide and 26 m long (two linked cars), and are rubber-tyred. Platforms are 52 m long, long enough for two units. One unit can carry 156 passengers.