Total posts : 45366
I agree that the results follow from the assumpions. It is the assumptions that I think are wrong. The 50% efficiency assumption is already known to be wrong. Nobody seems to have a transmitter with efficiency that high. Transmiter efficiency can be in the single digits, or less, with poor impedance matching to the antenna. Ground resistance is totally unknown, but it is likely to be high because it is hard to avoid a poor ground plane in a Part 15 AM installation. It could easily be a lot more than 100 ohms. The loading coil resistance can be unknown. This, at least, can be found if Q can be measured. 20 ohms is not bad at the high end of the band. It could be over 100 ohms at the low end, since a good loading coil is difficult to make at 540 kHz.
This is why I think it is important to get field strength measurements from installations. I have a couple of breadboards containing Signetics NE 602s, which I used in homodyne receivers I tested years ago. I’ll try to make a crude field strength meter to get some real data about the efficiencies in actual installations.