Public Radio Satellite System
Encyclopedia
The Public Radio Satellite System (or 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. 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.
s 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. The equipment included a receiving dish and an analog audio receiver
manufactured by network hardware
manufacturer Coastcom http://www.coastcom.com under the master contract held by Rockwell. The dish was aimed to Westar 1
, the satellite used by PRSS at its debut, and the receiver was able to tune in to the several audio channels uplinked by NPR on two transponder
s 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 15 channels. There were additional channels that were available and accessible by special Coastcom receivers that were frequency agile. The additional channels were rented out to various programming including commercial content. Each transponder was labeled on the receiver as "NPR A" and "NPR B", 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.
Some NPR member stations also invested in satellite uplink equipment, so they themselves could contribute programming to the PRSS network without having to send their program feeds either via phone line or on a mailed audio tape
to NPR in Washington for them to uplink on the PRSS. 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.
feeds instead of analog, and automated receiver selection and tuning of feeds (using a dedicated PC).
This system was known as the SOSS, or Satellite Operations Support System. Analog feeds were discontinued, and instead uplinked digitally (but still in SCPC fashion) using Musicam encoding, and received using ComStream ABR-700 digital audio satellite demodulators, which tapped off the 70 MHz IF bus of a Satellite System Corporation Model 4421 downconverter, which was in essence the main satellite receiver
for the system, taking in the L-band
input from the dish's LNB
.
There were seven ABR-700 demodulators (or "demods") used: six for audio program feeds (each demod was referred to as "NPR A" through "NPR F"), and a seventh for reception of data only (called the Downlink Service Channel, or DSC). The DSC demod was interfaced to the SOSS PC, which ran custom control software running under OS/2
. Using frequency & transponder data for program feeds received from the DSC demod (which was tuned to a fixed transponder and SCPC frequency), the software would automatically tune any one of the six audio demods to whatever program feeds the station would want to receive (the 1st generation analog PRSS receivers had to be tuned manually for each feed).
DACS messaging functions were also integrated into the SOSS PC using its software and the DSC demod. The six audio demods were controlled by the SOSS PC via several RS-485 serial connections from a board installed in the PC called the ARTIC board ("A Real-Time Interface Co-Processor"), with each demod respectively equipped with a RS-485 serial control interface.
The SOSS not only provided high-quality digital audio for NPR and other program feeds, but provided automatic tuning, as well as recording control for audio servers in radio automation systems (and stand-alone audio recorders as well) of NPR programming feeds. The SOSS could also be configured via its control software to tune in live feeds (such as breaking news
and live programs) and apply such to a dedicated demod, which could be any of the six installed.
) manufactured by International Datacasting http://www.datacast.com. Program feeds are requested and set up at a special internet-accessible web site (known as the ContentDepot Portal) that member stations can log on
to, where they can subscribe to specific programs and live feeds. The subscribed programs are then delivered via satellite as a file transfer to the storage receiver in the form of MP2
-encoded ACM-based WAV
files, which then can be imported into a station's automation and/or playback system.
Live feeds are sent in the ContentDepot system as streaming MP2 audio, sent over the same satellite transponder, but as an IP multicast
stream (as opposed to a file transfer for pre-recorded programs) which is decoded by a special streaming audio
receiver (called a stream decoder) set to the IP multicast addresses assigned for live audio streams on the satellite transponder used by ContentDepot.
Some components of the previous SOSS still are in use in the ContentDepot era: one of the ABR-700 demods (as well as the downconverter) is still used by NPR as a "squawk box" for verbal announcements regarding programming to NPR stations.
Public Radio International
Public Radio International is a Minneapolis-based American public radio organization, with locations in Boston, New York, London and Beijing. PRI's tagline is "Hear a different voice." PRI is a major public media content creator and also distributes programs from many sources...
(PRI), and American Public Media
American Public Media
American Public Media is the second largest producer of public radio programs in the United States of America after NPR. Its non-profit parent, American Public Media Group, also owns and operates radio stations in Minnesota, California, and Florida. Its station brands are Minnesota Public Radio,...
(APM), as well as independent public radio program producers, to distribute programming via satellite to public radio
Public broadcasting
Public broadcasting includes radio, television and other electronic media outlets whose primary mission is public service. Public broadcasters receive funding from diverse sources including license fees, individual contributions, public financing and commercial financing.Public broadcasting may be...
stations across the United States.
The PRSS is maintained by NPR's Distribution division at their Network Operations Center
Network Operations Center
A network operations center is one or more locations from which control is exercised over a computer, television broadcast, or telecommunications network....
(NOC), located at NPR's headquarters in Washington, DC. A backup NOC is located at Minnesota Public Radio
Minnesota Public Radio
Minnesota Public Radio , is the flagship National Public Radio member network for the state of Minnesota. With its three services, News & Information, Classical Music and The Current, MPR operates a 42-station regional radio network in the upper Midwest serving over 8 million people...
'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, 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 lineTelephone line
A telephone line or telephone circuit is a single-user circuit on a telephone communication system...
s furnished by AT&T
AT&T
AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...
, which were configured in a "round-robin" loop interconnecting the major NPR member stations at the time.
Member stations invested in earth station
Earth station
A ground station, earth station, or earth terminal is a terrestrial terminal station designed for extraplanetary telecommunication with spacecraft, and/or reception of radio waves from an astronomical radio source. Ground stations are located either on the surface of the Earth, or within Earth's...
receiving equipment to be a part of the new PRSS. The equipment included a receiving dish and an analog audio receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
manufactured by network hardware
Networking hardware
Networking hardware typically refers to equipment facilitating the use of a computer network. Typically, this includes routers, switches, hubs, gateways, access points, network interface cards, Networking cables, network bridges, modems, ISDN adapters, firewalls and other equipments.In the most...
manufacturer Coastcom http://www.coastcom.com under the master contract held by Rockwell. The dish was aimed to Westar 1
Westar 1
Westar 1 was America's first domestic and commercially launched geostationary communications satellite, launched by Western Union and NASA on April 13, 1974. It was built by Hughes for Western Union, using the HS-333 platform of spin-stabilized satellites. Westar 1 was the first of five Westar...
, the satellite used by PRSS at its debut, and the receiver was able to tune in to the several audio channels uplinked by NPR on two transponder
Transponder (Satellite communications)
A communications satellite’s transponder, is the series of interconnected units which form a communications channel between the receiving and the transmitting antennas .A transponder is typically composed of:...
s 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 15 channels. There were additional channels that were available and accessible by special Coastcom receivers that were frequency agile. The additional channels were rented out to various programming including commercial content. Each transponder was labeled on the receiver as "NPR A" and "NPR B", with each tunable to any desired IF
Intermediate frequency
In communications and electronic engineering, an intermediate frequency is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called...
-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
Dbx, Inc.
dbx, Inc. is an American producer of professional audio recording equipment. It was founded by David E. Blackmer in 1971. The original company goal was: "To get closer to the realism of a live performance." Its early products were based on the concept of using decibel expansion which gave the...
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
Total harmonic distortion
The total harmonic distortion, or THD, of a signal is a measurement of the harmonic distortion present and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency...
. 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
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
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
Short message service
Short Message Service is a text messaging service component of phone, web, or mobile communication systems, using standardized communications protocols that allow the exchange of short text messages between fixed line or mobile phone devices...
regarding programming and other information.
Some NPR member stations also invested in satellite uplink equipment, so they themselves could contribute programming to the PRSS network without having to send their program feeds either via phone line or on a mailed audio tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
to NPR in Washington for them to uplink on the PRSS. Some of the very first stations to have their own uplink facilities to PRSS were KUT
Kut
Al-Kūt is a city in eastern Iraq, on the left bank of the Tigris River, about 160 kilometres south east of Baghdad. the estimated population is about 374,000 people...
in Austin, Texas
Austin, Texas
Austin is the capital city of the U.S. state of :Texas and the seat of Travis County. Located in Central Texas on the eastern edge of the American Southwest, it is the fourth-largest city in Texas and the 14th most populous city in the United States. It was the third-fastest-growing large city in...
, and Minnesota Public Radio, both in 1980.
Satellite Operations Support System (SOSS)
Around 1994, the 1st generation analog PRSS system was upgraded to a new system using digital audioDigital audio
Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...
feeds instead of analog, and automated receiver selection and tuning of feeds (using a dedicated PC).
This system was known as the SOSS, or Satellite Operations Support System. Analog feeds were discontinued, and instead uplinked digitally (but still in SCPC fashion) using Musicam encoding, and received using ComStream ABR-700 digital audio satellite demodulators, which tapped off the 70 MHz IF bus of a Satellite System Corporation Model 4421 downconverter, which was in essence the main satellite receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
for the system, taking in the L-band
L band
L band refers to four different bands of the electromagnetic spectrum: 40 to 60 GHz , 1 to 2 GHz , 1565 nm to 1625 nm , and around 3.5 micrometres .-NATO L band:...
input from the dish's LNB
Low-noise block converter
A low-noise block downconverter is the receiving device of a parabolic satellite dish antenna of the type commonly used for satellite TV reception...
.
There were seven ABR-700 demodulators (or "demods") used: six for audio program feeds (each demod was referred to as "NPR A" through "NPR F"), and a seventh for reception of data only (called the Downlink Service Channel, or DSC). The DSC demod was interfaced to the SOSS PC, which ran custom control software running under OS/2
OS/2
OS/2 is a computer operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively. The name stands for "Operating System/2," because it was introduced as part of the same generation change release as IBM's "Personal System/2 " line of second-generation personal...
. Using frequency & transponder data for program feeds received from the DSC demod (which was tuned to a fixed transponder and SCPC frequency), the software would automatically tune any one of the six audio demods to whatever program feeds the station would want to receive (the 1st generation analog PRSS receivers had to be tuned manually for each feed).
DACS messaging functions were also integrated into the SOSS PC using its software and the DSC demod. The six audio demods were controlled by the SOSS PC via several RS-485 serial connections from a board installed in the PC called the ARTIC board ("A Real-Time Interface Co-Processor"), with each demod respectively equipped with a RS-485 serial control interface.
The SOSS not only provided high-quality digital audio for NPR and other program feeds, but provided automatic tuning, as well as recording control for audio servers in radio automation systems (and stand-alone audio recorders as well) of NPR programming feeds. The SOSS could also be configured via its control software to tune in live feeds (such as breaking news
Breaking news
Breaking news, also known as a special report or news bulletin, is a current event that broadcasters feel warrants the interruption of scheduled programming and/or current news in order to report its details. Many times, breaking news is used after the news network has already reported on this story...
and live programs) and apply such to a dedicated demod, which could be any of the six installed.
ContentDepot
In 2007, the SOSS was retired for the newest and current system of the PRSS, the ContentDepot. The ContentDepot no longer uses linear feeds of SCPC-based digital audio bitstreams like the SOSS. Instead, it uses a dedicated TCP/IP-based one-way connection uplinked via satellite from PRSS, which is received by a storage receiver (a combination satellite data receiver & file serverFile server
In computing, a file server is a computer attached to a network that has the primary purpose of providing a location for shared disk access, i.e. shared storage of computer files that can be accessed by the workstations that are attached to the computer network...
) manufactured by International Datacasting http://www.datacast.com. Program feeds are requested and set up at a special internet-accessible web site (known as the ContentDepot Portal) that member stations can log on
Login
Login is the method whereby a user obtains access to a computer system.Login may also refer to:*Magazines:** LOGiN, published by Enterbrain** ;login:, published by USENIX* Login, Carmarthenshire, an hamlet in Carmarthenshire...
to, where they can subscribe to specific programs and live feeds. The subscribed programs are then delivered via satellite as a file transfer to the storage receiver in the form of MP2
MPEG-1 Audio Layer II
MPEG-1 Audio Layer II or MPEG-2 Audio Layer II is a lossy audio compression format defined by ISO/IEC 11172-3 alongside MPEG-1 Audio Layer I and MPEG-1 Audio Layer III...
-encoded ACM-based WAV
WAV
Waveform Audio File Format , is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs...
files, which then can be imported into a station's automation and/or playback system.
Live feeds are sent in the ContentDepot system as streaming MP2 audio, sent over the same satellite transponder, but as an IP multicast
IP Multicast
IP multicast is a method of sending Internet Protocol datagrams to a group of interested receivers in a single transmission. It is often employed for streaming media applications on the Internet and private networks. The method is the IP-specific version of the general concept of multicast...
stream (as opposed to a file transfer for pre-recorded programs) which is decoded by a special streaming audio
Streaming media
Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
receiver (called a stream decoder) set to the IP multicast addresses assigned for live audio streams on the satellite transponder used by ContentDepot.
Some components of the previous SOSS still are in use in the ContentDepot era: one of the ABR-700 demods (as well as the downconverter) is still used by NPR as a "squawk box" for verbal announcements regarding programming to NPR stations.