VLF Experiments...



2006-02-21 : VLF RDF spectrum .

Strong local noise, but the european VLF transmitters (as of 2006) are easily visible. Wonder what the intermittant "orange crap" below 15 kHz is...





2008-07-31 : Broadband VLF spectrum .

Received with the SDR-IQ receiver (software defined radio for the USB port). Antenna is DL4YHF's VLF radio direction finder antenna (crossed ferrite loops), but since SDR-IQ has only one antenna input, this is not an RDF-spectrum.





2008-08-08 : 50 Hz hum plot.

Equipment: Differential E-field receiver with FM wireless link to the radio shack. Around 20:25, the antenna fell over caused by a gust of wind ;-)

The same receiver is occasionally used to send a live VLF audio stream to http://abelian.org/vlf/ .

During the night, the 50 Hz hum amplitude (green graph) seemed to "step" by about 3 dB (01:00, 05:00), while the total signal power (blue graph) remained constant. Most likely, the variation of the total power is caused by chances in sferics activity :

Hum removal in SL's "Filter" window. The dark green curve is the input spectrum, the cyan graph is the output spectrum. You can see the notches in the passband; these are 50 Hz harmonics removed by the automatic notch filter. This is also the typical setting for VLF streaming.



2008-08-29: ZEVS is back again

Russian ZEVS transmitter on 82 Hz

Russian ZEVS transmitter on 82 Hz

Russian ZEVS transmitter on 82 Hz

Spectrograms with Russian ZEVS VLF signal on 82 Hz (+/-).
Each symbol is 4 minutes long. The signal was easily visible on a portable E-field receiver, using a 10 or 20 mHz FFT resolution.


2008-10-02 : VLF stream from Cumiana, Italy, with Schuman resonances. Details about the receiver on Renato's VLF openlab site.

The red graph shows a long-term average, here: added the FFTs over 30 minutes. FFT size is 262144 points, equivalent receiver bandwidth 63 mHz (remember... mHz is milli-Hertz; not Mega-Hertz ;-)

"Acoustic VLF" : An attempt towards direction finding

2008-08-25 : "Stereo spectrogram" for the PALAOA realtime viewer (details.).
The left audio channel adds cyan colour to the display, the right adds the red component.