Goto Section: 73.658 | 73.665 | Table of Contents
Revised as of September 1, 2021
Goto Year:2020 |
§ 73.664 Determining operating power.
(a) The operating power of each TV visual transmitter shall normally be
determined by the direct method.
(b) Direct method, visual transmitter. The direct method of power
determination for a TV visual transmitter uses the indications of a
calibrated transmission line meter (responsive to peak power) located
at the RF output terminals of the transmitter. The indications of the
calibrated meter are used to observe and maintain the authorized
operating power of the visual transmitter. This meter must be
calibrated whenever any component in the metering circuit is repaired
or replaced and as often as necessary to ensure operation in accordance
with the provisions of § 73.1560 of this part. The following calibration
procedures are to be used:
(1) The transmission line meter is calibrated by measuring the average
power at the output terminals of the transmitter, including any
vestigial sideband and harmonic filters which may be used in normal
operation. For this determination the average power output is measured
while operating into a dummy load of substantially zero reactance and a
resistance equal to the transmission line characteristic impedance.
During this measurement the transmitter is to be modulated only by a
standard synchronizing signal with blanking level set at 75% of peak
amplitude as observed in an output waveform monitor, and with this
blanketing level amplitude maintained throughout the time interval
between synchronizing pulses.
(2) If electrical devices are used to determine the output power, such
devices must permit determination of this power to within an accuracy
of Â±5% of the power indicated by the full scale reading of the
electrical indicating instrument of the device. If temperature and
coolant flow indicating devices are used to determine the power output,
such devices must permit determination of this power to within an
accuracy of Â±4% of measured average power output. The peak power output
is the power so measured in the dummy load multiplied by the factor
1.68. During this measurement the input voltage and current to the
final radio frequency amplifier stage and the transmission line meter
are to be read and compared with similar readings taken with the dummy
load replaced by the antenna. These readings must be in substantial
(3) The meter must be calibrated with the transmitter operating at 80%,
100%, and 110% of the authorized power as often as may be necessary to
maintain its accuracy and ensure correct transmitter operating power.
In cases where the transmitter is incapable of operating at 110% of the
authorized power output, the calibration may be made at a power output
between 100% and 110% of the authorized power output. However, where
this is done, the output meter must be marked at the point of
calibration of maximum power output, and the station will be deemed to
be in violation of this rule if that power is exceeded. The upper and
lower limits of permissible power deviation as determined by the
prescribed calibration, must be shown upon the meter either by means of
adjustable red markers incorporated in the meter or by red marks placed
upon the meter scale or glass face. These markings must be checked and
changed, if necessary, each time the meter is calibrated.
(c) Indirect method, visual transmitter. The operating power is
determined by the indirect method by applying an appropriate factor to
the input power to the final radio-frequency amplifier stage of the
transmitter using the following formula:
Transmitter output power = Ep Ã— Ip Ã— F
Ep = DC input voltage of the final radio-frequency amplifier stage.
Ip = DC input current of the final radio-frequency amplifier 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 carrier frequency and transmitter output power.
(iii) Using the transmitter manufacturer's measurement data submitted
to the FCC for type acceptance as shown in the instruction book
supplied to the licensee.
Note: Refer to § 73.1560 for aural transmitter output power levels.
[ 44 FR 58732 , Oct. 11, 1979, as amended at 48 FR 44805 , Sept. 30, 1983;
49 FR 4210 , Feb. 3, 1984; 49 FR 22092 , May 25, 1984; 49 FR 49851 , Dec.
24, 1984; 50 FR 26568 , June 27, 1985; 54 FR 9806 , Mar. 8, 1989.
Redesignated at 58 FR 62555 , Nov. 29, 1993]
Goto Section: 73.658 | 73.665
Goto Year: 2020 |
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