Low frequency transmissions require specialized, usually custom-made, equipment. Because of the time frame of this application, we desire to maximize the amount of time available for over-the-air experimentation. As a result, we will utilize the Raspberry Pi, a credit-card sized computer, as the transmitter; custom low-pass filters to regulate transmitter operating frequency; and software to produce and manage the waveforms in this experiment. This transmission system allows us to focus on the development of our antenna network.
Horizontal Electric Dipole
A ground dipole consists of two grounded electrodes buried in the earth, separated by a distance, and linked by overhead transmission lines to the transmitter. We will experiment with a variety of designs, materials, and configurations; focusing on practical uses for this impractical and electrically short antenna.
Spiral Top-Loaded Antenna
Alan Melina and Finbar O’Connor developed an efficient LF Band antenna for use in a limited space. The top-load of the antenna has both an inductive and capacitive component. Despite the limited dimensions of the antenna, Melina and O’Connor successfully brought it to resonance on 136 kHz with a relatively small loading coil (Strobbe, 2009).
A helical antenna consists of a conducting wire wound in the form of a helix and mounted over a ground plane. The feed line is connected between the bottom of the helix and the ground plane with part of a loading coil mounted in the vertical section of the antenna.