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