Natural Radio Project

My first recordings, 3 tiny diffuse whistlers:

1st diffuse whistler, recorded at 23:10
2nd diffuse whistler, recorded at 23:13
3rd diffuse whistler, recorded at 23:17
A screenshot from Spectrum Lab and the complete audio file, filtered with the hum filter from SpectrumLab

Project description

First of all, I built the LNVA 24-20 low noise amplifier which I found at www.vlf.it.
My LNVA has an integrated 9 V block battery for portable operation.

I started the recordings with a wire loop, but this arrangement gave poor result. A lot of 50Hz hum because it was to close to the house.

Then I decided to use a 25m wire antenna and approx. 30m RG58 feed line. This arrangement gave me a lot more signal and much better S/N. For sferics reception I used Spectrum Lab from DL4YHF with the integrated hum filter.

I was recording from 1.1.2013 till 3.1.2013 after sunset. The first evening was very quiet, only normal sferics. On the second evening, the sound changed a little bit and very loud tweeks could be recorded. The weather was also changing and some snow was expected for the next days.
The third evening was yet louder and after a few minutes of recording, I could hear my first whistler! Two more followed within the next few minutes. The whistler were diffused and just above the noise level, but I could hear them clearly in my headphones.

Update 2022-04-03: I processed the WAV file with Spectrum Lab using the hum filter and discovered more then 10 diffuse whistlers after the 50 Hz noise was removed.
   

The equipment

LNVA 24-20, more information on: http://www.vlf.it
LNVA 24-20, front view
LNVA 24-20, rear view
LNVA 24-20, inside view
LNVA 24-20, detailed view
The wire antenna