The high frequency (F1) is greater than 10 MHz, the first very low frequency (F2) is between 200 Hz to 50 kHz, and the extremely low frequency (F3) is between 2 Hz to 5 kHz.
A system, method and apparatus for controlling buried devices by means of a very low frequency (VLF) modulated magnetic field capable of providing through-the-earth (TTE) communications.
The transceiver converts the text-data into analog data packets, modulates the packets onto ultra-low-frequency carrier waves, and transmits the signal to the surface receiver.
Text data are encoded into data packets, modulated onto ultra-low-frequency electric carrier waves, and transmitted through the earth by the surface electrodes to a subsurface transceiver.
A portable wireless through-the-earth bi-directional communication system for sending, receiving text-data using ultra-low-frequency electric current and earth as the conductive media.
The system may be used in fields such as manufacturing integrated circuits, and low- and very-low-frequency geophones, and other low- and very-low-frequency acoustic detectors.