§  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 § 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
   § 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]