Part 15 AM System Analysis vs. NEC Software Mar 9, 2019 13:20:56 GMT
Post by Rich on Mar 9, 2019 13:20:56 GMT
(The information below was posted earlier today on Part15.org. The text clip quoted below was in reference to the graphic also included below.)
RE: "These formulas are designed for higher power transmitters, not part 15. For example my part 15 has no loading coil. The efficiency is higher then he mentions. So his calculations are not that useful I think”
My public, quotable comments to that above text clip are:
- The formulas contained in the NEC4.2 software used to create the data for the graphic included below are valid and accurate at all power levels, including the range of nanowatts to megawatts. To state otherwise provides incorrect and misleading information. Anyone wishing to verify this is free to do so by their own research, or by contacting Gerald Burke or Andrew Poggio of the Lawrence Livermore National Laboratory in California, the co-authors of that software.
- A Hamilton AM1000 RangemasterTM transmitter includes an internal loading coil wound on a ferrite core. That coil cannot have zero resistance to the r-f current flowing through it, and does contribute to the losses present in the load impedance of the transmitter output signal — which reduces the power output (efficiency) of all transmit systems using that transmitter. This copper-wire coil is wound on a circular core, and is visible at the upper left of the transmitter enclosure shown in the "tuning" video currently linked at "https://www.youtube.com/watch?v=dennCHkoQ0w"
- A rather optimistic estimate of 15 ohms was included for the loss of an internal loading coil at system resonance, as the third item from the bottom of the list showing the complete system description that was analyzed in my graphic below.
In my engineering opinion, the chart below shows about the maximum performance to be expected for a Part 15 AM system meeting FCC §15.219(a) and §15.219(b), for the complete conditions stated there.
Of course operators are free to install any system configuration they wish, at their own risk. However, if its performance significantly exceeds that shown in the chart below, it might be more likely to receive a field inspection from the FCC — even if that installation configuration was/is suggested or endorsed by the manufacturer or agents of the transmitter that system uses.