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Staying Connected with STLs
Moseley Associates has offered the SL9003Q Starlink for many years. A recently introduced configuration is the SL-9003Q-2SLAN that provides one AES data stream (44.1kHz sample rate stereo pair) with simplex data at 544kb/s rate. If the user wanted to build a full-duplex data system, he could opt to install a Moseley Lanlink as well, which (by way of duplexers, using the same path with the same antennas) inserts a data transceiver on both ends of the system, with Ethernet in and out. The Lanlink operates in the 900MHz ISM band, and it is an independent system that could be used with any 950MHz band STL. By the way, you could use it right along with your old analog STL.
And perhaps you have no need for high-speed data to your transmitter site; you just want a digital STL to take advantage of the sound quality. There are plenty of radios out there that will do just that. TFT offers Model 460, which can carry three AES data streams (stereo embedded, 32kHz sample rate, using 256 QAM) in an occupied bandwidth of less than 500kHz. Again, an advantage of a digital scheme: This radio is specified to have a 10E-6 BER for a -84dBm signal level. Obviously you can't do that with an analog radio.
Harris' digital radio STL is the CD link, which will transport one 16-bit AES data stream and two RS-232 data channels. An option is to replace the RS-232 data with two 6kHz audio channels or a single 12kHz audio channel.
Armstrong recently introduced the Xlink. This is a microprocessor-controlled analog radio with the standard features — three SCA inputs, one composite and one mono input. It is frequency agile, making it handy as a spare for a station group. Armstrong can provide a two- or four-channel digital encoder/decoder pair that can be loaded in the Xlink, making a cost-effective upgrade to digital.
Broadcast Electronics offers the Big Pipe system — a mainframe chassis that uses plug-in interface modules for specific functions, such as audio transport or Ethernet. The link ends communicate via unlicensed channels in the 5.3GHz ISM band. BE has also recently introduced Big Pipe LT, which is a single-rack unit version that allows for Ethernet connectivity up to a 45Mb/s data rate.
My policy for many years has been to operate radio STLs as back-ups, making use of the reliability and flexibility of digital (wired) STLs for my mains. If you were to implement the same policy you'd have many choices from which to pick for equipment.
Harris/Intraplex is kind of the granddaddy in wireline STL equipment. The STL HD is a package of two 4RU frames that contain modules that transport the AES data stream (later transmitted over the analog transmitter) along with another set of modules that transport Ethernet. (This set would be used to carry the UDP data packet stream that carries the MPS and SPS should you opt to use the exgine architecture for HD Radio implementation).
APT offers the Worldnet Oslo, a 3RU frame system that uses plug-in modules to transport as many as 14 stereo audio pairs. Options for the audio transport are non-compressed, linear; 48kHz sampling, 24-bit resolution Apt-x or Enhanced Apt-x. The system can operate over T1, E1 or IP networks. APT has also partnered with Pulsecom to distribute the PCAU and HD PCAU for wired digital loops.
Musicam USA has a product known as Team, which is a mainframe-based system that makes use of plug-in modules that carry out specific functions such as audio transport. The Superlink is another mainframe system made by Musicam. It too uses plug-in modules for specific functions like audio transport; in addition it can bond multiple ISDN circuits — as many as three — for a total of 384kb/s data throughput. Aside from ISDN, the Superlink can also communicate via Ethernet, ATM or T1.
Options abound for digital transport to your transmitter site. As the means by which entertainment content streams are distributed increases in number, it's wise to build an STL system that has not only great initial capability but also scalability as well. TCP/IP capability for your transmitter site is now nearly a must-have, and generally speaking, digital transport of program audio is just easier than the old analog methods and it sounds better anyway.
Irwin is a broadcast engineer in Seattle.
Manufacturers of STL equipment and accessories
DB Elettronica Telecomunicazioni
Digital Juke Box
Kathrein, Scala Division
Microwave Radio Communications
Superior Broadcast Products
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