Requests have been noted for some method of operating a Part 15 AM transmitter from an elevated location without needing a path to an earth ground, and while meeting FCC Part 15.219(b). The link below could be one possibility for doing this.
The comments section on the left hand side of the page describes the physical and electrical configuration. A ~3-meter antenna fed at the base becomes part of an off-center-fed dipole, where the PC board traces in the transmitter form the short side of the dipole.
The capacitive reactance at the feedpoint of this configuration as modeled is over 30,000 ohms, so the internal loading coil in some Part 15 AM transmitters probably will not be sufficient to match it, and added series inductance will be necessary.
There is no "lightning ground" conductor leading away from the transmitter, but if this system is installed inside a condo, for example, there is little exposure to lightning risks.
With 35 milliwatts of Z-matched power from the transmitter, this system can produce a groundwave field of about 150 µV/m at a distance of 475 meters (0.3 miles) over earth of average conductivity -- which would provide fairly useful reception to good AM receivers.
http://i62.photobucket.com/albums/h85/rfry-100/Part15AM_NoGround-1.jpg
The comments section on the left hand side of the page describes the physical and electrical configuration. A ~3-meter antenna fed at the base becomes part of an off-center-fed dipole, where the PC board traces in the transmitter form the short side of the dipole.
The capacitive reactance at the feedpoint of this configuration as modeled is over 30,000 ohms, so the internal loading coil in some Part 15 AM transmitters probably will not be sufficient to match it, and added series inductance will be necessary.
There is no "lightning ground" conductor leading away from the transmitter, but if this system is installed inside a condo, for example, there is little exposure to lightning risks.
With 35 milliwatts of Z-matched power from the transmitter, this system can produce a groundwave field of about 150 µV/m at a distance of 475 meters (0.3 miles) over earth of average conductivity -- which would provide fairly useful reception to good AM receivers.
http://i62.photobucket.com/albums/h85/rfry-100/Part15AM_NoGround-1.jpg