Goto Section: 73.1560 | 73.1580 | Table of Contents
Revised as of October 1, 2020
Goto Year:2019 |
§ 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 § 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
Goto Section: 73.1560 | 73.1580
Goto Year: 2019 |
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