During
the past few years, I have focused my study on 0,1 Hz to 40 Hz frequency
spectrum, measuring and recording the instant variations of the magnetic field
and not its absolute value.
Unfortunately,
in the vicinity of big cities, the levels of signals from natural sources are
1.000-30.000 times lower than those of signals transmitted by our technological
civilization. For this reason, the
use of filters in the electronic circuit is imperative.
