Hi ELF und sub-ELF fans,

I have to report about very good success on reception in the ELF  and sub-ELF range. This evening arround 16 UTC i successfully received 5 Schumann resonances with my T antenna in the garden in 8m above ground, 400m outside the city.

I significantly improved the circuit:

Higher input resistance, now 100 MOhm
Lower cut off frequency using a 3 stage LPF arround 3 kHz
also a lower cuf off frequency of the high pass now below 10 Hz
Removed the electronic parts from the breadboard and re-soldered them on a copper board. This was essential! because there were undefined conducting layers on the breadboard which affected the working point of the JFET.

New preamp: https://dl.dropboxusercontent.com/u/19882028/VLF/20141005_162621.jpg
New schematic: https://dl.dropboxusercontent.com/u/19882028/VLF/DK7FC%20ELF%20preamp%20V2.jpg

Results (shown without sferic blanking)
wideband 0...24 kHz: https://dl.dropboxusercontent.com/u/19882028/VLF/NewELF_wide_10s_1.46HzFFT.png  also showing the frequency response of the circuit
0...1 kHz: https://dl.dropboxusercontent.com/u/19882028/VLF/NewELF_0to1kHz_10s_1.46HzFFT.png
0...55 Hz: https://dl.dropboxusercontent.com/u/19882028/VLF/0...55Hz_5sperdiv_45mHzFFT_garden3rd.png
ZEVS:https://dl.dropboxusercontent.com/u/19882028/VLF/ZEVS_garden3rd.png  (not so strong this time. QRN?)

What about these sferics below 2 kHz? Is it normal that they are so strong? Or is it a technical problem? Can i improve the situation by harder attenuating the spectrum above 2 kHz? At least this is what i want to try.


Next ideas for improving the SNR of ZEVS and Schumann:
Increasing the R of the LPF to 2.2...3.3 MOhm
Maybe trying 1 GOhm for biasing the JFETs gate to 6V
Improving the insulation of the antenna feeds (simple cord now, without ceramic between).
Trying to rise the antenna 1 meter
Fixing the feed point by a ceramic insulator

73, Stefan/DK7FC