Goto Section: 73.1560 | 73.1580 | Table of Contents
FCC 73.1570
Revised as of October 1, 2008
Goto Year:2007 |
2009
Sec. 73.1570 Modulation levels: AM, FM, TV and Class A TV aural.
(a) The percentage of modulation is to be maintained at as high a level as
is consistent with good quality of transmission and good broadcast service,
with maximum levels not to exceed the values specified in paragraph (b).
Generally, the modulation should not be less than 85% on peaks of frequent
recurrence, but where lower modulation levels may be required to avoid
objectionable loudness or to maintain the dynamic range of the program
material, the degree of modulation may be reduced to whatever level is
necessary for this purpose, even though under such circumstances, the level
may be substantially less than that which produces peaks of frequent
recurrence at a level of 85%.
(b) Maximum modulation levels must meet the following limitations:
(1) AM stations. In no case shall the amplitude modulation of the carrier
wave exceed 100% on negative peaks of frequent recurrence, or 125% on
positive peaks at any time.
(i) AM stations transmitting stereophonic programs not exceed the AM maximum
stereophonic transmission signal modulation specifications of stereophonic
system in use.
(ii) For AM stations transmitting telemetry signals for remote control or
automatic transmission system operation, the amplitude of modulation of the
carrier by the use of subaudible tones must not be higher than necessary to
effect reliable and accurate data transmission and may not, in any case,
exceed 6%.
(2) FM stations. The total modulation must not exceed 100 percent on peaks
of frequent reoccurrence referenced to 75 kHz deviation. However, stations
providing subsidiary communications services using subcarriers under
provisions of Sec. 73.319 concurrently with the broadcasting of stereophonic or
monophonic programs may increase the peak modulation deviation as follows:
(i) The total peak modulation may be increased 0.5 percent for each 1.0
percent subcarrier injection modulation.
(ii) In no event may the modulation of the carrier exceed 110 percent (82.5
kHz peak deviation).
(3) TV and Class A TV stations. In no case shall the total modulation of the
aural carrier exceed 100% on peaks of frequent recurrence, unless some other
peak modulation level is specified in an instrument of authorization. For
monophonic transmissions, 100% modulation is defined as +/−25 kHz.
(c) If a limiting or compression amplifier is employed to maintain
modulation levels, precaution must be taken so as not to substantially alter
the dynamic characteristics of programs.
[ 44 FR 58735 , Oct. 11, 1979, as amended at 47 FR 13165 , Mar. 29, 1982; 49 FR 14508 , Apr. 12, 1984; 49 FR 15081 , Apr. 17, 1984; 49 FR 27147 , July 2, 1984;
49 FR 47610 , Dec. 6, 1984; 49 FR 48312 , Dec. 12, 1984; 51 FR 26251 , July 22,
1986; 56 FR 64872 , Dec. 12, 1991; 65 FR 30004 , May 10, 2000]
Goto Section: 73.1560 | 73.1580
Goto Year: 2007 |
2009
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