Sec.  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]