§  73.757   System specifications for single-sideband (SSB) modulated
emissions in the HF broadcasting service.

   (a) System parameters --(1) Channel spacing. In a mixed DSB, SSB and
   digital environment (see Resolution 517 (Rev.WRC-03)), the channel
   spacing shall be 10 kHz. In the interest of spectrum conservation, it
   is also permissible to interleave SSB emissions midway between two
   adjacent DSB channels, i.e. , with 5 kHz separation between carrier
   frequencies, provided that the interleaved emission is not to the same
   geographical area as either of the emissions between which it is
   interleaved. In an all inclusive SSB environment, the channel spacing
   and carrier frequency separation shall be 5 kHz.

   (2) Equivalent sideband power. When the carrier reduction relative to
   peak envelope power is 6 dB, an equivalent SSB emission is one giving
   the same audio-frequency signal-to-noise ratio at the receiver output
   as the corresponding DSB emission, when it is received by a DSB
   receiver with envelope detection. This is achieved when the sideband
   power of the SSB emission is 3 dB larger than the total sideband power
   of the DSB emission. (The peak envelope power of the equivalent SSB
   emission and the carrier power are the same as that of the DSB
   emission.)

   (b) Emission characteristics --(1) Nominal carrier frequencies. Nominal
   carrier frequencies shall be integral multiples of 5 kHz.

   (2) Frequency tolerance. The frequency tolerance shall be 10 Hz.

   Note 1 to paragraph (b)(2): The ITU suggests that administrations avoid
   carrier frequency differences of a few hertz, which cause degradations
   similar to periodic fading. This could be avoided if the frequency
   tolerance were 0.1 Hz, a tolerance which would be suitable for SSB
   emissions.

   Note 2 to paragraph (b)(2): The SSB system adopted for the bands
   allocated exclusively to HF broadcasting does not require a frequency
   tolerance less than 10 Hz. The degradation mentioned in Note 1 occurs
   when the ratio of wanted-to-interfering signal is well below the
   required protection ratio. This remark is equally valid for both DSB
   and SSB emissions.

   (3) Audio-frequency band. The upper limit of the audio-frequency band
   (at--3 dB) of the transmitter shall not exceed 4.5 kHz with a further
   slope of attenuation of 35 dB/kHz and the lower limit shall be 150 Hz
   with lower frequencies attenuated at a slope of 6 dB per octave.

   (4) Modulation processing. If audio-frequency signal processing is
   used, the dynamic range of the modulating signal shall be not less than
   20 dB.

   (5) Necessary bandwidth. The necessary bandwidth shall not exceed 4.5
   kHz.

   (6) Carrier reduction (relative to peak envelope power). In a mixed
   DSB, SSB and digital environment, the carrier reduction shall be 6 dB
   to allow SSB emissions to be received by conventional DSB receivers
   with envelope detection without significant deterioration of the
   reception quality.

   (7) Sideband to be emitted. Only the upper sideband shall be used.

   (8) Attenuation of the unwanted sideband. The attenuation of the
   unwanted sideband (lower sideband) and of intermodulation products in
   that part of the emission spectrum shall be at least 35 dB relative to
   the wanted sideband signal level. However, since there is in practice a
   large difference between signal amplitudes in adjacent channels, a
   greater attenuation is recommended.

   [ 70 FR 46677 , Aug. 10, 2005]