Total posts : 45366
Adding a bit more detail:
Ermi wrote “Rich reports that, to get this much radiated power at 1620 kHz, it is necessary to apply about 80 watts to a 3-meter antenna with 20 ohms of loss resistance, and about 4 watts when the antenna is elevated 6 meters. This implies an increase in efficiency by a factor of about 20 for the elevated antenna.
Just to remind that the added efficiency is not produced because the Part 15 tx and 3-m whip are elevated, per se, but because of the added radiation from the long conductor(s) connecting the tx chassis to the buried r-f ground.
Some believe that the added signal strength from elevated (whip/mast) Part 15 AM systems is due to better line-of-sight paths from the 3-m whip. But a NEC evaluation shows that it is due to radiation from the longer conducting path to r-f ground.
Rich also says that about a half watt applied to a lossless 1/4 wave monopole produces the field strength the FCC measured. This is true, because a lossless electrically short antenna has only slightly less gain than a lossless 1/4 wave monopole (469 mW is about a half watt).
NEC shows that a lossless 3-m monopole system on 1620 kHz has a peak gain of 4.77 dBi. This value is 0.38 dB less than that for a lossless 1/4-wave monopole. So if this 1/4-wave system needed 1/2 watt of applied power to produce a given field strength at a given distance, then this 3-m monopole would need about 9% more, or 0.545 watts.
So we are in essential, but not exact agreement.