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The Public Radio Satellite System (PRSS) is the interconnected satellite-distributed network managed by NPR (National Public Radio), and used by NPR, Public Radio International (PRI), and American Public Media (APM), as well as independent public radio program producers, to distribute programming via satellite to public radio stations across the United States. The PRSS is maintained by NPR's Distribution division at their Network Operations Center (NOC), located at NPR's headquarters in Washington, DC.〔Public Radio Satellite System, (), ''About PRSS''〕 A backup NOC is located at Minnesota Public Radio's facilities in St. Paul, Minnesota, in the event of a catastrophe or other situation that would occur at the main NOC's location in Washington. The NOC oversees and monitors all elements and operations of the PRSS system, from outgoing feeds from NPR, APM and PRI, and incoming feeds from member stations. ==History== The PRSS first made its debut in 1979,〔Current.org, (), ''Public radio's new interconnection''〕 using the then-new technology (for broadcasting) of satellite distribution. Prior to the PRSS and starting from NPR's founding in 1971, NPR and its member stations used a network of broadcast-quality leased telephone lines furnished by AT&T, which were configured in a "round-robin" loop interconnecting the major NPR member stations at the time. Member stations invested in earth station receiving equipment to be a part of the new PRSS in the form of a grant from the Corporation for Public Broadcasting to cover all costs with the stipulation that the radio station must be on the air for a minimum of 18 hours per day and have at least 3 full-time employees. After a period of years the stipulations would cease and the earth station would become the property of the radio station. The equipment included a receiving dish and an analog audio receiver manufactured by network hardware manufacturer Coastcom () under the master contract held by Rockwell. The dish was aimed to Westar 1, the satellite used by PRSS at its debut, and later to Westar IV after the former satellite was retired in 1983. The receiver was able to tune into the several audio channels uplinked by NPR on two transponders on the satellite. The audio channels, transmitted in analog, were multiplexed on each transponder using SCPC (Single Channel Per Carrier) transmission. The receivers were pre-programmed for 12 channels. There were additional channels that were available and accessible by special Coastcom receivers that were frequency agile or by the upgrade of a microchip to the existing 12 channel demodulators already installed at the radio station. The additional channels were rented out to various programming including commercial content. Later, channels 13 and 14 were for a period leased to the CMSS (the Classical Music Satellite Service), a third party produced service outside of NPR, that was available to public radio stations who paid to air the service. Each transponder was labeled on the receiver as "NPR A" and "NPR B", with a red illuminated display of the channel number on each receiver with each tunable to any desired IF-based SCPC frequency. This first generation analog PRSS system yielded about a 40dB ratio of analog (recovered) signal to noise for each audio channel. dbx modules that were set for 3:1 were used to increase the dynamic range of the system. Typically this worked well but for some low frequencies the distortion exceeded 10 percent THD. Also the dBx modules varied in how they tracked the compressed audio so the expanded audio was not an exact representation of what was compressed at the uplink. Many of these problems were resolved when the PRSS moved to the digital-based SOSS system, mentioned later in this article. One of the channels transmitted was a low-speed data channel that could be decoded with a leased-line telephone modem connected to the Coastcom receiver, called the DACS channel, or the Direct Access Communications System. It acted as a 1-way wire that provided NPR stations with text messages regarding programming and other information. Select NPR member stations were provided with satellite uplink equipment to meet the mission of NPR to provide access to the satellite system by independent, 3rd parties who would enhance the programming of public radio beyond NPR's own programming as well as provide for back-hauls of news reports to be aired on NPR's news programs or feeds of promotional material and other not for broadcast or "closed circuit" content. These 15 strategically located uplinks located in regions throughout the country were also to provide revenue from use by commercial entities who would pay for NPR to transmit its programming via its satellite system. Because NPR, at the time, had the only operational satellite network that could transmit in high quality, full fidelity, stereo sound, several music based commercial programs were distributed via NPR's satellite system such as Rockline, Hollywood Live, several live concerts, and some Westwood One content. These uplinks allowed producers of program to send pre-recorded or live material to an uplink in their region instead of having to send by mail or haul it by expensive telco lines to NPR's MOTC (Main Origination Technical Center, the analog PRSS predecessor to NPR's NOC) Washington uplink. Some of the very first stations to have their own uplink facilities to PRSS were KUT in Austin, Texas, and Minnesota Public Radio, both in 1980, and KUSC, Los Angeles, who provided the bulk of the commercial radio revenue uplinks, at about the same time. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Public Radio Satellite System」の詳細全文を読む スポンサード リンク
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