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The radiation efficiency of a monopole antenna system is related to the ratio of the radiation resistance of the unburied conductors of the antenna system at the operating frequency to all of the dissipative resistances in the antenna system [radiation resistance + the r-f resistance of the loading coil + the r-f resistance of the buried conductor(s) against which the monopole is driven].
If the r-f resistance of the loading coil and/or the r-f resistance of the buried conductor(s) against which the radiating conductors are driven are relatively low, then antenna system radiation efficiency is relatively high. But also the r-f bandwidth of the antenna system is relatively low. System tuning/matching is more difficult, not as stable with changing conditions, and even when optimized may reduce the high-frequency content of the original program audio that is present in the output audio of an AM receiver — making it sound “muffled” or of “telephone quality.”
For a given, unburied set of radiating conductors, an increase in the r-f resistance of the loading coil and/or the buried conductor(s) against which the monopole is driven will improve the audio quality that can be transmitted. But also this will reduce the distance that such a signal usefully can be received (other things equal).
This is the quandary.
