Total posts : 45366
Is there a recommended practice?
AFAIK, the hardware/circuit needed to “tune” a typical Part 15 AM antenna is restricted to adjustment of a loading coil, whether that coil is provided within the transmitter by the transmitter manufacturer, or is external to the transmitter enclosure and provided by the final installer/user/tester.
If the inductive reactance of that loading coil is perfectly adjusted, it can exactly offset the capacitive reactance of electrically short radiating conductors in the AM broadcast band (conductors totaling 3 meters or less, if meeting §15.219) — which “resonates” that antenna system.
BUT… even with a resonant load, the input SWR of an antenna system still depends on the “real,” or non-j term of its impedance. That real term is the sum of the antenna radiation resistance, the loading coil resistance, and the r-f ground resistance.
Antenna system load SWR is a function of the value of that real term with respect to the resonant load value that the transmitter is designed to drive.
So far I have not seen such a specification to be provided by any manufacturer of commercial transmitters marketed for Part 15 AM.
I know of no commercially available Part 15 AM transmitters either certified or not that include the hardware needed to provide a theoretically perfect (loss-free) match for equal power supplied to all antenna system load impedances in the range of 10 j0 ohms to 100 j0 ohms.
Sorry that my recent posts here have been a bit technical, but then that is the nature of this subject.