Goto Section: 73.49 | 73.53 | Table of Contents
FCC 73.51
Revised as of December 4, 2012
Goto Year:2011 |
2013
§ 73.51 Determining operating power.
(a) Except in those circumstances described in paragraph (d) of this
section, the operating power shall be determined by the direct method.
The direct method consists of either:
(1) using a suitable instrument for determining the antenna's input
power directly from the RF voltage, RF current, and phase angle; or
(2) calculating the product of the licensed antenna or common point
resistance at the operating frequency (see § 73.54), and the square of
the indicated unmodulated antenna current at that frequency, measured
at the point where the resistance has been determined.
(b) The authorized antenna input power for each station shall be equal
to the nominal power for such station, with the following exceptions:
(1) For stations with nominal powers of 5 kW, or less, the authorized
antenna input power to directional antennas shall exceed the nominal
power by 8 percent.
(2) For stations with nominal powers in excess of 5 kW, the authorized
antenna input power to directional antennas shall exceed the nominal
power by 5.3 percent.
(3) In specific cases, it may be necessary to limit the radiated field
to a level below that which would result if normal power were delivered
to the antenna. In such cases, excess power may be dissipated in the
antenna feed circuit, the transmitter may be operated with power output
at a level which is less than the rated carrier power, or a combination
of the two methods may be used, subject to the conditions given in
paragraph (c) of this section.
(i) Where a dissipative network is employed, the authorized antenna
current and resistance, and the authorized antenna input power shall be
determined at the input terminals of the dissipative network.
(ii) Where the authorized antenna input power is less than the nominal
power, subject to the conditions set forth in paragraph (c) of this
section, the transmitter may be operated at the reduced power level
necessary to supply the authorized antenna input power.
(c) Applications for authority to operate with antenna input power
which is less than nominal power and/or to employ a dissipative network
in the antenna system shall be made on FCC Form 302. The technical
information supplied on section II-A of this form shall be that
applying to the proposed conditions of operation. In addition, the
following information shall be furnished, as pertinent:
(1) Full details of any network employed for the purpose of dissipating
radio frequency energy otherwise delivered to the antenna (see
§ 73.54).
(2) A showing that the transmitter has been type accepted or notified
for operation at the proposed power output level, or, in lieu thereof:
(i) A full description of the means by which transmitter output power
will be reduced.
(ii) Where the proposed transmitter power output level(s) is less than
90% of the rated power of the transmitter, equipment performance
measurements must be made to confirm that the station transmissions
conform to the emission limitation specified in § 73.44, under all
conditions of program operation.
(iii) A showing that, at the proposed power output level, means are
provided for varying the transmitter output within a tolerance of ±10
percent, to compensate for variations in line voltage or other factors
which may affect the power output level.
(d) When it is not possible or appropriate to use the direct method of
power determination due to technical reasons, the indirect method of
determining operating power (see paragraphs (e) and (f) of this
section) may be used on a temporary basis. A notation must be made in
the station log indicating the dates of commencement and termination of
measurement using the indirect method of power determination.
(e) The antenna input power is determined indirectly by applying an
appropriate factor to the input power to the last radio-frequency power
amplifier stage of the transmitter, using the following formula:
Where:
Antenna input power = Ep × Ip × F
Ep=DC input voltage of final radio stage.
Ip=Total DC input current of final radio stage.
F= Efficiency factor.
(1) If the above formula is not appropriate for the design of the
transmitter final amplifier, use a formula specified by the transmitter
manufacturer with other appropriate operating parameters.
(2) The value of F applicable to each mode of operation must be
determined and a record kept thereof with a notation as to its
derivation. This factor is to be established by one of the methods
described in paragraph (f) of this section and retained in the station
records.
(f) The value of F is to be determined by one of the following
procedures listed in order of preference:
(1) If the station had previously been authorized and operating by
determining the antenna input power by the direct method, the factor F
is the ratio of the antenna input power (determined by the direct
method) to the corresponding final radio frequency power amplifier
input power.
(2) If a station has not been previously in regular operation with the
power authorized for the period of indirect power determination, if a
new transmitter has been installed, or if, for any other reason, the
determination of the factor F by the method described in paragraph
(f)(1) of this section is impracticable:
(i) The factor F as shown in the transmitter manufacturer's test
report, if such a test report specifies a unique value of F for the
power level and frequently used; or
(ii) The value determined by reference to the following table:
Factor(F) Method of modulation Maximum rated carrier power Class of
amplifier
0.70 Plate 1 kW or less
.80 Plate 2.5 kW and over
.35 Low level 0.25 kW and over B
.65 Low level 0.25 kW and over BC^1
.35 Grid 0.25 kW and over
^1 All linear amplifier operation where efficiency approaches that of
class C operation.
(Secs. 4, 5, 303, 48 Stat., as amended, 1066, as amended, 1068, 1082,
as amended; 47 U.S.C. 154, 155, 303. Interpret or apply secs. 301, 303,
307, 48 Stat. 1081, 1082, as amended, 47 U.S.C. 301, 303, 307)
[ 37 FR 7516 , Apr. 15, 1972, as amended at 42 FR 36827 , July 18, 1977;
42 FR 61863 , Dec. 7, 1977; 44 FR 36036 , June 20, 1979; 47 FR 28387 ,
June 30, 1982; 48 FR 38477 , Aug. 24, 1983; 48 FR 44805 , Sept. 30, 1983;
49 FR 3999 , Feb. 1, 1984; 49 FR 4210 , Feb. 3, 1984; 49 FR 49850 , Dec.
24, 1984; 50 FR 24521 , June 11, 1985; 52 FR 10570 , Apr. 2, 1987]
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Goto Section: 73.49 | 73.53
Goto Year: 2011 |
2013
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