World Broadcasting Unions Digital Radio User Manual - page 56
DIGITAL RADIO GUIDE
TERRESTRIAL TRANSMISSION SYSTEMS - HD RADIO
56
4.4.8
Infrastructure Requirements
At this writing, approximately 250 HD Radio stations have commenced operations in the
United States with an additional 300 stations currently licensed to commence operations
in the coming year. Consumer receivers went on sale in early 2004 and considerable
work has been done on implementation options that may significantly reduce installation
costs at many stations.
In particular, the use of separate antenna radiating systems has been successfully
demonstrated which can eliminate the need for combiners at higher power FM stations.
11
Furthermore development of a “Gen-2” system
12
that will multiplex the HD Radio data
stream at the studio site, much as is done with composite analogue STLs, is expected to
be introduced in the coming year. Low-level combining is preferred and has been shown
to be cost effective at power levels up to an analogue 7 kw transmitter power output.
11
See IBOC Space Diversity Testing, Talmadge Ball, Proceedings of NAB 2003 BEC; also see “Dual Antenna Report”
Denny & Associates at http://www.nab.org/scitech/fccfilingattachmentb.pdf.
12
Gen 2 refers to a planned evolution in HD system design that will permit multiplexing of all digital signals at the studio to
achieve significant reductions in feeder link bandwidth requirements.