FCC 73.757 Revised as of December 4, 2012
Goto Year:2011 |
§ 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
(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
(5) Necessary bandwidth. The necessary bandwidth shall not exceed 4.5
(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
(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]
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