§  73.758   System specifications for digitally modulated emissions in the HF
broadcasting service.

   (a) For digitally modulated emissions, the Digital Radio Mondiale (DRM)
   standard shall be employed. Both digital audio broadcasting and
   datacasting are authorized. The RF requirements for the DRM system are
   specified in paragraphs (b) and (c), of this section.

   (b) System parameters --(1) Channel spacing. The initial spacing for
   digitally modulated emissions shall be 10 kHz. However, interleaved
   channels with a separation of 5 kHz may be used in accordance with the
   appropriate protection criteria appearing in Resolution 543 (WRC-03),
   provided that the interleaved emission is not to the same geographical
   area as either of the emissions between which it is interleaved.

   (2) Channel utilization. Channels using digitally modulated emissions
   may share the same spectrum or be interleaved with analog emissions in
   the same high frequency broadcasting (HFBC) band, provided the
   protection afforded to the analog emissions is at least as great as
   that which is currently in force for analog-to-analog protection.
   Accomplishing this may require that the digital spectral power density
   (and total power) be lower by several dB than is currently used for
   either DSB or SSB emissions.

   (c) Emission characteristics --(1) Bandwidth and center frequency. A
   full digitally modulated emission will have a 10 kHz bandwidth with its
   center frequency at any of the 5 kHz center frequency locations in the
   channel raster currently in use within the HFBC bands. Among several
   possible "simulcast" modes are those having a combination of analog and
   digital emissions of the same program in the same channel, that may use
   a digital emission of 5 kHz or 10 kHz bandwidth, next to either a 5 kHz
   or 10 kHz analog emission. In all cases of this type, the 5 kHz
   interleaved raster used in HFBC shall be adhered to in placing the
   emission within these bands.

   (2) Frequency tolerance. The frequency tolerance shall be 10 Hz. See
   Section 73.757(b)(2), notes 1 and 2.

   (3) Audio-frequency band. The quality of service, using digital source
   coding within a 10 kHz bandwidth, taking into account the need to adapt
   the emission coding for various levels of error avoidance, detection
   and correction, can range from the equivalent of monophonic FM
   (approximately 15 kHz) to the low-level performance of a speech codec
   (of the order of 3 kHz). The choice of audio quality is connected to
   the needs of the broadcaster and listener, and includes the
   consideration of such characteristics as the propagation conditions
   expected. There is no single specification, only the upper and lower
   bounds noted in this paragraph.

   (4) Modulation. Quadrature amplitude modulation (QAM) with orthogonal
   frequency division multiplexing (OFDM) shall be used. 64-QAM is
   feasible under many propagation conditions; others such as 32-, 16- and
   8-QAM are specified for use when needed.

   (5) RF protection ratio values. The protection ratio values for
   analogue and digital emissions for co-channel and adjacent channel
   conditions shall be in accordance with Resolution 543 (WRC-03) as
   provisional RF protection ratio values subject to revision or
   confirmation by a future competent conference.

   [ 70 FR 46677 , Aug. 10, 2005]