Total posts : 45366
If 22.2 uW is, indeed, a “useful” Part 15 AM radiated power, it can be obtained within the restrictions of Section 15.219. This, after all, is a system efficiency of only .0222/100 =.0222 %. If I am correct in guessing that the causes for the inefficiency of the cited system are very high ground resistance and/or poor tuning, then special attention has to be paid to the ground and the tuning circuit.
I think that the SSTRAN tuning circuit, which is a capacitive input “L” network with a loading coil in series with the antenna, is a good one. I use it myself in my experimental transmitter. I am trying to improve its efficiency and its ease of use. I do not favor using a tuned transformer, which is less capable than the “L” network of obtaining a good impedance match between the transmitter and the antenna.