Re: LF: ZEVS RX ant question

["Markus Vester" <markusvester@aol.com>]

Hi Stefan,

 

here is the simple source follower circuit which picked up Zevs and Schumann resonances: http://df6nm.bplaced.net/VLF/ELF/source_follower.jpg . The browsable directory http://df6nm.bplaced.net/VLF/ELF/ also contains some spectrograms, an usr configuration, and a couple of wav files which were sampled at 250 samples/sec. In a postprocessing step, the strong 16.7 Hz harmonics have been notched out, and the wav file header has been modified for replay at 60x speed. What then sounds like statics are actually "Q-bursts", super strong lightning events which resonate globally in the earth / ionosphere cavity.

 

I also wonder why your low frequency range looks so noisy. I suspect that you might still have the noise blanker activated, which would be sheer poison! It will modulate itself onto the usually strong 50 Hz line and also onto a possible DC offset, generating sidebands that will splatter all over the ELF spectrum. My recipe was trying to keep everything linear, with the local 16.7 Hz line only a few dB below fullscale, and Zevs only about - 91 dB.

 

Best 73,

Markus (DF6NM)

 

From: DK7FC

Sent: Sunday, September 28, 2014 4:28 PM

To: rsgb_lf_group@blacksheep.org

Subject: LF: ZEVS RX ant question

HI VLF,

Yesterday i tried again to receive ZEVS. I didn't know if it was on air but gave it a try. Recorded about 2 hours of the VLF spectrum received on my T antenna (i.e. E-field). I also used a source follower (J310) but added a 3 stage RC filter in front of the gate. I thought i can afford some pF against ground now with the relatively large antenna which must have about 150 pF. I used this circuit: https://dl.dropboxusercontent.com/u/19882028/VLF/ZEVS%20test%20ant.jpg

But somehow the spectrum looks not as expected. While the MSKs are still strong, there is much noise below 2 kHz and the sferics appear to be quite weak. See: https://dl.dropboxusercontent.com/u/19882028/VLF/Garden%20T%20antenna%20VLF%201.png

I remember from tests with a small active antenna for VLF, where i used 100 MOhm resistors on the gate, that charged humidity caused much noise.
Could this be the same effect here?
Should i try to use a lower input impedance of the preamp?
Maybe you remember, there were certain transistors, several decades ago, they were called bipolar transistors, NPN and PNP. Maybe i should try one of them? :-)

 Advice is apprechiated. Where are the experts?

73, Stefan/DK7FC