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Dendritic Ground Systems

3 min read
air earth insulated rod, 1 m VLF wave →
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Dendritic Ground Systems places antennas in the ground instead of the air. Each receiver is an insulated copper rod sealed inside an acrylic conduit and sunk vertically one meter into the earth, isolated from the soil around it, after a construction for wireless telegraphy antennas that Jozef Murgaš patented in 1907. At very low frequencies, below about 30 kHz, the antenna picks up sferics from lightning strikes thousands of kilometers away, whistlers that have traveled out along the Earth’s magnetic field lines and back, and the military and navigation beacons that occupy that part of the spectrum. Since the audio and radio frequency domains overlap in this band, the signal goes straight from a high-impedance preamp into a sound interface with no radio in between. No license is required for listening, only transmitting.

One buried rod is a single root, and several of them spread across a site, each with its own preamp and power, form a branching system under the ground that senses and connects, which references the behavior of slime tube networks and pea roots which I am currently exploring in my radio protocol research. The ground in the title does double work, since it is both the soil the antennas live in and the electrical ground these receivers depend on. The project is at an early stage, so what follows is a mood board rather than a description of a finished piece.

A night field station under a starry sky: a tall mast with guy lines marked by green glow sticks, and a laptop lit up on a folding table in the scrub.
A night listening station in the field, mast and guy lines marked with glow sticks.
A spectrogram of a VLF recording, dark with a dense field of thin vertical streaks, each one a lightning stroke somewhere on the planet.
67 seconds of VLF from my own recordings. Each vertical streak is a sferic, the impulse from a lightning stroke somewhere on the planet.
Sheet 1 of Jozef Murgaš's 1907 US patent 860,051, Constructing Antennae of Wireless Telegraphy, showing two long insulated rods sunk vertically into hatched earth, wired to transmitting and receiving circuits above ground.
Jozef Murgaš, US patent 860,051, 1907. Antennas for wireless telegraphy constructed in the earth.
A black and white photograph of a railway line running through a border strip, with rows of concrete posts and coils of barbed wire strung across the tracks.
Reference image. Wire strung between posts along a line in the ground, already an antenna whether anyone meant it or not.
A toroidal coil wound in red wire with blue tape, lying in the grass between two alligator clips.
The tuning coil, wound on a ferrite toroid and matched to the capacitance of the buried rod.
A bare green printed circuit board for a small JFET preamplifier, lying on a wooden bench.
The JFET preamp board that sits between the rod and the sound interface. Design: A portable VLF preamplifier, UltraMSK.

Radio Protocol Research · sig-x · Plant-to-Plant Protocols · Physarum Controlled Oscillators