Total posts : 45366
As I’ve posted several times now, anything that reduces losses in the antenna system will improve its radiation efficiency. Major losses include those in the r-f ground system, and in the loading coil.
So one goal is to use a loading coil with enough reactance to resonate the short radiator on the operating frequency, with low(est) r-f losses.
Likewise, lowering the r-f resistance in the buried ground system will improve Part 15 AM antenna system efficiency, for the reasons I’ve recently posted.