Re: LF: ZEVS RX ant question, now success

[wolf_dl4yhf <dl4yhf@freenet.de>]

Hi Stefan,

The 82 Hz signal looks good... you may even catch a glimpse of "DX" from the US and their 60 Hz mains with that setup.
It's several dB down on ZEVS but sometimes good copy here, on an active E-field probe out in the woods (far away from old PC monitors which sometimes operated near 60 Hz).

73,
  Wolf  DL4YHF .

Am 03.10.2014 21:38, schrieb Stefan Schäfer:

Hi VLF,

This evening i received ZEVS for the first time in the garden :-)

I used nearly the same circuit than in my email below. However, i found that the J310 was damaged! Remembers me on the old discussion if protecting diodes are necessary or not :-) But this is a large antenna, compared to an active E probe like the PA0RDT-antenna...
Now i've replaced the JFET and added two 4148 protecting diodes on the gate against ground and plus.
Reception looks much better now:
0...24kHz: https://dl.dropboxusercontent.com/u/19882028/VLF/wide_500msperdiv_732mHzFFT_garden3rd.png
0...4 kHz: https://dl.dropboxusercontent.com/u/19882028/VLF/0...4kHz_500msperdiv_732mHzFFT_garden3rd.png
0...500 Hz: https://dl.dropboxusercontent.com/u/19882028/VLF/0...500Hz_500msperdiv_732mHzFFT_garden3rd.png
ZEVS in 7.6 mHz, 40 sec scroll rate: https://dl.dropboxusercontent.com/u/19882028/VLF/ZEVS_1st.png

It looks like i need some more gain on the lower frequencies. Will modify the circuit a bit...

73, Stefan/DK7FC

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