Total posts : 45366
Ermi writes: The estimates of radiated power in Rich’s post seem high. Based on discussions on another recent thread, the estimate of about 20 uW is about right for a fairly good installation at the upper end of the band, but not at 540 kHz.
Yet this is the way the numbers fall for the conditions I gave.
In the thread where ~ 20 µW ERP was discussed, the r-f output power from the tx applied to the antenna system input terminals is an unknown — even though the relevant FCC NOUO gave a measured tx PA DC input power of 1200 mW in that setup. But of necessity by the measured field it produced, the power accepted by the antenna system would have been very low, probably indicating a poor impedance match between the tx output and the input terminals of the antenna system (including whatever matching coil was included). In that case most of the output power of the tx was reflected by its mis-matched load impedance, and dissipated as heat in the output stage of the transmitter.
OTOH, my calculations used 50 mW of applied (tx output) power to each antenna system and each antenna system had a perfect impedance match to the transmitter, so as to compare their far-field coverage potentials on 540 kHz and 1650 kHz with other things equal.
What I have gathered from several FCC NOUOs, and the Part 15 AM tx certification data I’ve read is that the radiated power from these tx+antenna systems with 90-100 mW of DC input power to the final r-f amplifier shows some combination of suprisingly low DC-rf conversion efficiency in the tx PA, a poor impedance match to the antenna system, and high r-f ground loss.
One of the things that would reduce radiated power at 540 kHz, in addition to the smaller radiation resistance, is appreciably increased loading coil loss resistance.
I’ll be glad to re-run the numbers using whatever coil loss and r-f ground loss anyone wants to consider.
What is lacking is good data.
True for measured data, but probably the real performance of Part 15 AM setups can be calculated with higher accuracy than it can be measured.
Of course that calls for accurate numbers for the calculation entries, and they need to be based on measured data and/or experience. Due to the skills and instrumentation needed and the low powers involved in Part 15, none of this is easy to get for the average hobbyist, unfortunately.