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I did not mean to suggest that the Q of the coil I described in my post(which is just over 200) is the best that can be done. The point I wanted to make is that the Q available with coils is lower than what is desired.
In the Low Power AM Broadcasters Handbook, a loading coil loss resistance of 2 ohms is assumed. The inductive reactance required at the high end of the AM BCB is about 3000 ohms. (Interestingly, elevating the antenna greatly increases the radiation resistance, but does not significantly reduce the required inductive reactance.) For 2 ohms of loading coil loss, the required Q of the coil is 3000/2 = 1500. This high a Q is just not available with coils. The HP(Agilent) model 4342A Q meter has a maximum reading of 1000. The manufacturer clearly did not expect the need for a measuring the Q of a coil higher than that.
Having said that, I was truly impressed with the measured Q of 620 on Table 2 in the linked article. There are calculated Qs higher than that in the article, but calculated Qs are often overestimates. This high Q reading caused me to read some other articles in the series, specifically, # 0, # 26, and # 29. The descriptions of “contrawound” coils were particularly interesting. It may be that improved loading coil loss can be obtained by using contrawound coils. Even with this higher Q, the loading coil loss would be about 5 ohms.