Goto Section: 73.319 | 73.333 | Table of Contents
Revised as of September 1, 2021
Goto Year:2020 |
§ 73.322 FM stereophonic sound transmission standards.
(a) An FM broadcast station shall not use 19 kHz Â±20 Hz, except as the
stereophonic pilot frequency in a transmission system meeting the
(1) The modulating signal for the main channel consists of the sum of
the right and left signals.
(2) The pilot subcarrier at 19 kHz Â±2 Hz, must frequency modulate the
main carrier between the limits of 8 and 10 percent.
(3) One stereophonic subcarrier must be the second harmonic of the
pilot subcarrier (i.e., 38 kHz) and must cross the time axis with a
positive slope simultaneously with each crossing of the time axis by
the pilot subcarrier. Additional stereophomic subcarriers are not
(4) Double sideband, suppressed-carrier, amplitude modulation of the
stereophonic subcarrier at 38 kHz must be used.
(5) The stereophonic subcarrier at 38 kHz must be suppressed to a level
less than 1% modulation of the main carrier.
(6) The modulating signal for the required stereophonic subcarrier must
be equal to the difference of the left and right signals.
(7) The following modulation levels apply:
(i) When a signal exists in only one channel of a two channel
(biphonic) sound transmission, modulation of the carrier by audio
components within the baseband range of 50 Hz to 15 kHz shall not
exceed 45% and modulation of the carrier by the sum of the amplitude
modulated subcarrier in the baseband range of 23 kHz to 53 kHz shall
not exceed 45%.
(ii) When a signal exists in only one channel of a stereophonic sound
transmission having more than one stereophonic subcarrier in the
baseband, the modulation of the carrier by audio components within the
audio baseband range of 23 kHz to 99 kHz shall not exceed 53% with
total modulation not to exceed 90%.
(b) Stations not transmitting stereo with the method described in (a),
must limit the main carrier deviation caused by any modulating signals
occupying the band 19 kHz Â±20 Hz to 125 Hz.
(c) All stations, regardless of the stereophonic transmission system
used, must not exceed the maximum modulation limits specified in
§ 73.1570(b)(2). Stations not using the method described in (a), must
limit the modulation of the carrier by audio components within the
audio baseband range of 23 kHz to 99 kHz to not exceed 53%.
[ 51 FR 17029 , May 8, 1986]
Goto Section: 73.319 | 73.333
Goto Year: 2020 |
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