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 plus-minus5% 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 plus-minus4% 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

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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 x Ip x 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]