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Another detail that was sketched over was the length of the copper ground rod used in the test. 8 or 10-foot length would perform dramatically better than a 3-footer.
According to the text of the Challenge report, all of those transmit systems tested used the same ground rod, the same installation geometry, the same carrier frequency, the same d-c input power to the final r-f amplifier, the same propagation path, and the same calibrated meter/setup/personnel to measure those (relative) fields.
The only variables left among all of these systems are personal bias, and the r-f powers existing at the bases of their ~ 3-m radiators — which are dependent on the designs of those r-f amplifiers, the output adjustments provided for them, and the understanding/skill of their operator(s) in maximizing the power that those systems can radiate while not exceeding FCC §15.219.
Such variables in the DeFelice Challenge have not been quantified, so far.
Rich, a.k.a. “Sparky”