Goto Section: 73.658 | 73.665 | Table of Contents
FCC 73.664
Revised as of October 1, 2007
Goto Year:2006 |
2008
Sec. 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 Sec. 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 ±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 ±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 agreement.
(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 × Ip × F
Where:
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 Sec. 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: 2006 |
2008
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