Goto Section: 73.258 | 73.277 | Table of Contents
Revised as of September 1, 2021
Goto Year:2020 |
§ 73.267 Determining operating power.
(a) The operating power of each FM station is to be determined by
either the direct or indirect method.
(b) Direct method. The direct method of power determination for an FM
station uses the indications of a calibrated transmission line meter
(responsive to relative voltage, current, or power) located at the RF
output terminals of the transmitter. This meter must be calibrated
whenever there is any indication that the calibration is inaccurate or
whenever any component of the metering circuit is repaired or replaced.
The calibration must cover, as a minimum, the range from 90% to 105% of
authorized power. The meter calibration may be checked by measuring the
power at the transmitter terminals while either:
(1) Operating the transmitter into the transmitting antenna, and
determining actual operating power by the indirect method described in
§ 73.267(c); or
(2) Operating the transmitter into a load (of substantially zero
reactance and a resistance equal to the transmission line
characteristic impedance) and using an electrical device (within Â±5%
accuracy) or temperature and coolant flow indicator (within Â±4%
accuracy) to determine the power.
(3) The calibration must cover, as a minimum, the range from 90% to
105% of authorized power and the meter must provide clear indications
which will permit maintaining the operating power within the prescribed
tolerance or the meter shall be calibrated to read directly in power
(c) Indirect method. The operating power is determined by the indirect
method by applying an appropriate factor to the input power to the last
radio-frequency power amplifier stage of the transmitter, using the
Transmitter output power = Ep Ã— Ip Ã— 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 the efficiency factor, F, established for the
authorized transmitter output power is to be used for maintaining the
operating power, even though there may be some variation in F over the
power operating range of the transmitter.
(3) The value of F is to be determined and a record kept thereof by one
of the following procedures listed in order of preference:
(i) Using the most recent measurement data for calibration of the
transmission line meter according to the procedures described in
paragraph (b) of this section or the most recent measurements made by
the licensee establishing the value of F. In the case of composite
transmitters or those in which the final amplifier stages have been
modified pursuant to FCC approval, the licensee must furnish the FCC
and also retain with the station records the measurement data used as a
basis for determining the value of F.
(ii) Using measurement data shown on the transmitter manufacturer's
test data supplied to the licensee; Provided, That measurements were
made at the authorized frequency and transmitter output power.
(iii) Using the transmitter manufacturer's measurement data submitted
to the FCC for type acceptance and as shown in the instruction book
supplied to the licensee.
(Secs. 4, 5, 303, 48 Stat., as amended, 1066, 1068, 1082 (47 U.S.C.
154, 155, 303))
[ 44 FR 58731 , Oct. 11, 1979, as amended at 45 FR 28141 , Apr. 28, 1980;
48 FR 38479 , Aug. 24, 1983; 49 FR 4210 , Feb. 3, 1984; 49 FR 49851 , Dec.
Goto Section: 73.258 | 73.277
Goto Year: 2020 |
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