| 词条 | Band I | ||||||||||||||||||||||||||||||||||||
| 释义 |
Band I is a range of radio frequencies within the very high frequency (VHF) part of the electromagnetic spectrum. The first time there was defined "for simplicity" in Annex 1 of "Final acts of the European Broadcasting Conference in the VHF and UHF bands - Stockholm, 1961"[1]. Band I ranges from 47 to 68 MHz for the European Broadcasting Area,[2] and from 54 to 88 MHz for the Americas[3] and it is primarily used for television broadcasting in line to ITU Radio Regulations (article 1.38). Channel spacings vary from country to country, with spacings of 6, 7 and 8 MHz being common. Television broadcasting usageIn the UK, Band I was originally used by the BBC for monochrome 405-line television;[4] likewise, the French former 455-line (1937-1939) then 441-line (1943-1956) transmitter on the Eiffel Tower in Paris, and some stations of the French monochrome 819-line system used Band I. Both 405-line and 819-line systems were discontinued in the mid-1980s. Other European countries used and still use Band I for 625-line analogue television, first in monochrome and later in colour. This is now being gradually phased out with the introduction of digital television in the DVB-T standard, which is not defined for VHF Band I, though some older receivers and some modulators do support it. In the United States, use of this band is for analog NTSC (ended June 12, 2009) and digital ATSC (current). Digital television has problems with impulse noise interference, particularly in this band. EuropeIn European countries that use System B for television broadcasting, the band is subdivided into three channels, each being 7 MHz wide:
Italy also uses a "outband" "channel C" (video : 82.25 MHz - audio : 87.75 MHz). It was used by the first transmitter brought in service by the RAI in Torino in the Fifties which was previously used in WW2 by the US to broadcast NTSC TV on channel A6 for military purposes, later donated to Italy, it had its video carrier shifted 1 MHz lower to accommodate the System B standard. This channel was also widely used by private local stations until the switch over to DVB-T. Some countries use slightly different frequencies or don't use Band 1 at all for terrestrial broadcast television. The fast growing of digital television as well as the susceptibility of this band to interference during E skip events in all European countries is accompanied by the progressive closedown of band I analog transmitters, e.g. former French-language Swiss Television transmitter at La Dôle near Geneva on channel E4 or French analog transmitters used by Canal Plus for its Pay-TV VHF network, e.g. Besançon (Lomont) and Carcassonne (Pic de Nore) both on French channel "L-3". Swiss VHF Band I transmitters are switched off untile 25/06/2007( Barillette ), and 26/11/2007, for Uetliberg, and Bantiger( German speaking area) French analog Canal Plus VHF band I are switched off until 2010. Russia and other former members of OIRTIn the countries that use System D television broadcast system, the channel allocation in the VHF-I band is as follows:
North AmericaThe band is subdivided into five channels for television broadcasting, each occupying 6 MHz (System M). Channel 1 is not being used for broadcasting anymore.
FM Radio UsageThe upper end of this band, 87.5 to 88 MHz, is the lower end of the FM radio band. In the United States, the FCC will occasionally issue a license for 87.9 MHz (though it only does so on rare occurrences and special circumstances; KSFH is the only standalone station that uses 87.9 currently); 87.7, which is approximately the same frequency as the audio feed of channel 6, is used by some television licenses to broadcast primarily to radio, such as Pulse 87's stations. In Japan and some former Soviet republics frequencies lower than 87MHz are still used for FM radio broadcasting. See also
References1. ^{{Cite web|url=http://www.ero.dk/46D34362-434B-45DF-A7C1-64A3F85F4FFD?frames=no&|title=Final acts of the European Broadcasting Conference in the VHF and UHF bands - Stockholm, 1961|last=|first=|date=|website=www.ero.dk|archive-url=|archive-date=|dead-url=|access-date=2019-01-09}} {{TVRband}}{{Audio broadcasting}}2. ^{{cite web|title=FM / TV Regional Frequency Assignment Plans|url=http://www.itu.int/en/ITU-R/terrestrial/broadcast/Pages/FMTV.aspx|accessdate=20 February 2017|publisher=ITU}} 3. ^{{cite web|title=Frequency Bands allocated to Terrestrial Broadcasting Services|url=http://www.itu.int/en/ITU-R/terrestrial/broadcast/Pages/Bands.aspx|accessdate=20 February 2017|publisher=ITU}} 4. ^{{cite book|last=Paulu|first=Burton|title=Television and Radio in the United Kingdom|url=https://books.google.com/books?id=_lv7awDml10C&pg=PA91|accessdate=11 April 2012|date=1981-10-01|publisher=U of Minnesota Press|isbn=9780816609413|page=91}} 2 : Broadcast engineering|Radio spectrum |
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