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]