Hello VLF-/ELF-enthusiasts,
I built a slightly modified symmetrical vertical antenna which is described from IW5BHY in http://www.vlf.it/immagine/minimal_E.html and I want let you to know
my experience with this antenna.
First we installed this antenna at DL0AO. DL0AO is in a rural area in the wood. But the result was very disappointing! Already light wind increased the noise by 20 to 30 dB from 5 Hz to
2 kHz and on frequencies around 20 kHz several phantom signals were present when wind was blowing. Even during quiet periods no Schumann-resonances were visible and
ZEVS was very weak and the S/N of the submarine-TXs around 20 kHz was comparable to our ground-loops or E-field antenna (again: when there was no wind).
Presumably the surrounding high trees in 20 to 100 m distance and (or?) the wire-mesh fence with a very rusty barbed wire on top, only 20 m away from the
antenna, was the reason.
So I installed the antenna in my garden at home. With my small T-Marconi-antenna the noise level is quite high at home and I did not expect too much advantage
with the symmetrical vertical antenna. But surprise, surprise! The S/N of the submarine-TXs is up to 10 dB better compared to the small marconi, ZEVS is good visible,
the Schumann-Resonances are clearly visible (both not visible with the marconi-antenna) and a weak test-signal on 8.270 kHz from DF6NM was 15 db above the noise.
Compared to our antennas at DL0AO the S/N of the submarine-TXs are only 3 to 5 dB lower, ZEVS and Schumann-resonances are comparable between home and DL0AO.
Summary:
The symmetrical vertical antenna is much more sensitive to environmental effects than a vertical working against ground.
But when you use an antenna working not against ground in areas where the ground is noisy (in my case urban area, single family houses, no industry, no electrified train)
satisfactorily reception of ELF- and VLF-signals is possible with a symmetrical vertical dipole.
Bernd, DF9RB (one sysop of the grabbers at DL0AO)
