Sec.  73.54   Antenna resistance and reactance measurements.

   (a) The resistance of an omnidirectional series fed antenna is measured at
   either  the base of the antenna without intervening coupling or tuning
   networks, or at the point the transmission line connects to the output
   terminals of the transmitter. The resistance of a shunt excited antenna may
   be measured at the point the radio frequency energy is transferred to the
   feed wire circuit or at the output terminals of the transmitter.

   (b) The resistance and reactance of a directional antenna shall be measured
   at the point of common radiofrequency input to the directional antenna
   system  after  the  antenna has been finally adjusted for the required
   radiation pattern.

   (c) A letter of notification must be filed with the FCC in Washington, DC,
   Attention: Audio Division, Media Bureau, when determining power by the
   direct method pursuant to  Sec. 73.51. The letter must specify the antenna or
   common  point  resistance  at  the  operating frequency. The following
   information must also be kept on file at the station:

   (1) A full description of the method used to make measurements.

   (2) A schematic diagram showing clearly all components of coupling circuits,
   the point of resistance measurement, the location of the antenna ammeter,
   connections to and characteristics of all tower lighting isolation circuits,
   static drains, and any other fixtures connected to and supported by the
   antenna, including other antennas and associated networks. Any network or
   circuit  component  used  to  dissipate radio frequency power shall be
   specifically identified, and the impedances of all components which control
   the level of power dissipation, and the effective input resistance of the
   network must be indicated.

   (d) AM stations using direct reading power meters in accordance with  Sec. 73.51,
   can either submit the information required by paragraph (c) of this section
   or submit a statement indicating that such a meter is being used. Subsequent
   station licenses will indicate the use of a direct reading power meter in
   lieu of the antenna resistance value in such a situation.

   [ 66 FR 20755 , Apr. 25, 2001,as amended at  67 FR 13231 , Mar. 21, 2002]