The following paragraph is from http://www.lwca.org/sitepage/part15/index.htm (Web page section What is "Part 15?' / Are the requirements hard to meet?)>> Among the various sections and subsections within Part 15 are a number of interesting provisions. One permits the use of up to 1 watt of power and a 15 meter long antenna between 160 - 190 kilohertz, in the longwave bands, with no license requirement. Another permits similar operation from 510 - 1705 kHz, in the medium wave band, with 1/10 of a watt and a 3-meter antenna. Yet another allows operation in a 14kHz-wide band centered at 13.56MHz, with a maximum field strength limit that works out to about 4.8mW into a dipole or a quarter-wave vertical over an elevated ground plane. <<
The above excerpt is applicable to 47CFR15, subparagraphs 217, 219 and 225(b). I can well appreciate the "old fashion" power cap of DC watts into the final amplifying stage of subparagraphs 217 and 219. I'm having trouble reconciling the max electric field strength proviso of sub paragraph 225(b) with the LWCA page's 4.8 milliwatts into a dipole, etc.
Can someone refer me to an article or two that discusses this conversion, that is, electric field strength measured at a specified distance to RF watts input to the dipole and ground plane antenna? I've tried to research this and wind up with equations that calculate the RF power a good part of 2 orders of magnitude higher than 4.8 mW. Most definitely, I am missing something by blindly trying to use these equations!
Thank you -
73 Frank Lotito K3DZ / WH2XHA