ELF receiver for

EM waves beyond 46 Hz



Institute Sv.

Peter, Sv. Peter 115, 6320 Sečovlje, Slovenia


The preliminary measurements on the territory

of Slovenia showed that, on this part of Europe, the great value of

noise is presented in the geomagnetic field. In order to meet

international recommendations we chose only the magnetometers for

one-second results of measurements for our geomagnetic observatory PIA

(Piran, Slovenia).


For better registration of geomagnetic pulsations, natural resonant

frequencies of the Earth and conditions in ionosphere we constructed a

broadband ULF/ELF (Ultra Low Frequency / Extremely Low Frequency)

receiver (Earth Receiver). It receives the frequency range from 1 mHz

to 46 Hz. The frequency range of measurements is in the transition

from the Earth’s magnetic field, which arises within the interior of

our planet, into the measurement of the electric field, which arises

primarily in the Earth’s atmosphere. It covers the wavelength Gm

(length ~ 109 m), which are waves of magnetic pulsations, and the

wavelength of Mm (lenght ~ 109 m), which are the waves of natural

resonance of the Earth. The natural resonant frequencies originating

from electric resonators of the Earth have been explored since the

middle of the past century and are relatively poorly known.

Geomagnetic pulsations, which originated from space and magnetosphere,

have been studied more than two hundred years. The frequencies of

geomagnetic pulsation are mainly influenced by changes in the

orientation of the interplanetary magnetic field and change in the

speed of solar wind. Due to interference, these waves appear on the

Earth’s surface as sudden changes in the magnetic field of different

frequencies, amplitudes, phases and polarizations. Because they do not

depend only from solar wind but also from geological conditions at the

site of measurement, they are also good detector of internal structure

of lithosphere of the Earth and hydrological researches.


We adopted the construction of our Earth Receiver to the specific

conditions of our territory. There is the highest density of electric

discharges in atmosphere in Europe and also seismic active area. For

the same reason we adopted also its installation on our observatory.

Measurements from Earth Receiver at the observatory beyond the

frequency of 1 Hz are parallel measurements of magnetometers. We

initially studied the conditions with antenna of receiver orientated

vertically. The frequency range from 5 Hz to 50 Hz has great content

of electromagnetic noise of artificial source. Except for controlling

the EM pollution of our environment, ULF/ELF receiver is also suitable

for: a) monitoring of atmospheric discharges and cores of storms; b)

electric discharges into the ionosphere; c) earthquake monitoring; d)

determination of the influence of magnetic pulsation on biosphere and;

e) monitoring of climate changes. The Earth Receiver is the only

measuring instrument for monitoring seismic events, which is placed

directly in the origin of earthquake disorders.


The global ULF wave power index is calculated from the measurement

data of magnetometers on the Earth's surface and on geostationary and

interplanetary satellites. It is in direct correlation with the speed

of the solar wind and therefore is very suitable for the presentation

of the situation in the space in vicinity of the Earth (Space

Weather). But it is in very poor correlation with geomagnetic indices

and should therefore be appropriately adapted to monitor the phenomena

in the Earth's surface and lithosphere.