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Unfortunately the 3-meter limit includes antenna, transmission line and ground lead, impose a strict limitation.
But anything physically buried BELOW the surface of the ground is fair game, and makes a major improvement on radiation distance.
At a minimum an 8-foot ground rod pounded into the earth and attached to the transmitter ground lead will provide both improved signal field and lightning safety.
But if you fan 64- radials out at surface level each about 30-feet or more, you will achieve the distance of which part 15 AM is capable.
The ground wires or rods located below ground are not able to radiate, but do provide the vital process of a “return” path for completing the RF output circuit. I’ll let someone else explain that.