Total posts : 45366
Ermi writes: Rich, The coil losses you reported are much too low. In practice, it is very difficult to get a loading coil Q higher than about 350, or so.
Very well, then here are the results for a Part 15 AM setup on 1650 kHz with a ground-mounted, 3-m, 1/2″ OD monopole using a coil Q of 100 (coil AC resistance = 29.7 ohms). The r-f ground resistance was set to 100 ohms, and the matched transmitter output power to 5 milliwatts, to use values you suggested earlier in this thread.
ERP = 0.0044 mW, inverse distance groundwave field at 29.6 meters = 0.669 mV/m.
The distance above is at the near field limit for this system defined by Kraus/Balanis as lambda/2*pi. So for greater distances the field will be ~inversely proportional to that increased distance ratio.
The 0.669 mV/m field at 29.6 meters is just a little above that which you defined earlier as being marginal for urban environments.
The performance of a system with these parameters seems much worse than reported by many Part 15 AM users, even those using ground-mounted antennas, so possibly these assumptions are not typical.
I am presently studying loading coils, and I will be posting in the future on Radio Joe’s loading coil thread.
Great, that will be good reading.
Have you measured the Q of Miniductor™ coils made by Barker & Williamson? I have read online references to the fact that some of them have measured Qs in the range of 500-700.
In any case, coil Q doesn’t have a large affect on Part 15 AM antenna system efficiency when its effective R is ~swamped by the r-f ground loss, as in this scenario.