VLF - ELF observations and recordings
Last updated 8th July 2001
Late in December 2000, I built a reasonably large " Octoloop" ( as described by Will Payne)
It has ~ 4 metres dia , 100pr.phone cable (200turns), built into 32mm copper pipe.
A large number of experiments were conducted during the ensuing 6 months. It was found
to be best suited to operation in the 1kHz.....22kHz frequency bands. It was also used
with moderate success for frequencies as low as 2Hz, and was able to receive the lower
4 Schumann resonances if conditions were favourable (no wind, loop movements).
The total of 200 turns is actually split into symmetrical groups of 20,30,and 50 turns each.
This allows series-parallel connection of various groups for experimentation.
The final configuration is now 2x parallel groups of 50 turns in series with another 2x 50
turns group. This gives a centre tapped 100 turn coil of low resistance (higher Q, also
allowing lower op-amp. input noise performance).
This configuration is now mostly used to receive VLF/ ELF spectra and proved quite
successful for "whistler" detection and recording. High order mains harmonics are a
limiting factor in this location, extending well up to 4kHz (!)
The loop coils are connected to a balanced input low noise pre-amp.which is located
directly under the Octoloop. The input of the low noise amp. is preceded by a 22kHz
L/C LPF and also a 1kHz L/C HPF.
Whistler detection is a bit difficult in my location, latitude being -31.3 deg. Furthermore,
the lower few kHz are unusable due to mains harmonics. So reception is limited to the
range from ~ 2.5kHz to 20kHz. The whistlers are not as nice and sharp nor as long in
duration as they probably appear at higher latitudes.
Here are some recent samples :