47 CFR § 73.57 - Remote reading antenna and common point ammeters.
Remote reading antenna and common point ammeters may be used without further authority according to the following conditions:
(a) Remote reading antenna or common point ammeters may be provided by:
(1) Inserting second radio frequency current sensing device directly in the antenna circuit with remote leads to the indicating instruments.
(2) Inductive coupling to radio frequency current sensing device for providing direct current to indicating instrument.
(3) Capacity coupling to radio frequency current sensing device for providing direct current to indicating instrument.
(4) Current transformer connected to radio frequency current sensing device for providing direct current to indicating instrument.
(5) Using transmission line current meter at transmitter as remote reading ammeter. See paragraph (c) of this section.
(6) Using the indications of the antenna (phase) monitor, provided that when the monitor is used to obtain remote reading indication of non-directional antenna base current, the monitor calibration can be independently made and maintained for each mode of operation.
(b) Devices used for obtaining remote reading antenna or common point current indications, except antenna monitor coupling elements, shall be located at the same point as, but below (transmitter side) the associated main ammeter.
(c) In the case of shunt-excited antennas, the transmission line current meter at the transmitter may be considered as the remote antenna ammeter provided the transmission line is terminated directly into the excitation circuit feed line, which shall employ series tuning only (no shunt circuits of any type shall be employed) and insofar as practicable, the type and scale of the transmission line meter should be the same as those of the excitation circuit feed line meter (meter in slant wire feed line or equivalent).
(d) Each remote reading ammeter shall be accurate to within 2 percent of the value read on its corresponding regular ammeter.
(e) All remote reading ammeters shall conform with the specifications for regular antenna ammeters.
(f) Meters with arbitrary scale divisions may be used provided that calibration charts or curves are provided at the transmitter control point showing the relationship between the arbitrary scales and the reading of the main meters.
(g) If a malfunction affects the remote reading indicators of the antenna or common point ammeter, the operating power may be determined by a method using alternative procedures as described in § 73.51.