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LF: Some improvements in VLF Rx

To: "[email protected]" <[email protected]>
Subject: LF: Some improvements in VLF Rx
From: VIGILANT Luis Fernández <[email protected]>
Date: Mon, 8 May 2017 08:57:48 +0000
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Thread-index: AQHSx9kqLov3ejSO8ky0ZlWew2jd+w==
Thread-topic: Some improvements in VLF Rx
This weekend could fix the QRM problem with the VLF E-probe. There was a ground loop at the 1pps from GPS
The ground of the GPS (and PC via USB) was routed to the audio transformer at the VLF signal side, not soundard side
So, the noise was going up by the VLF cable to the probe and caused a 20dB noise rise in MF/LF in the nearby MiniWhip
The VLF espectrogram has got clearer, but still contaminated. Specially at night, probably due to street led lights in the area
I'm using a separate first Fet at the probe, connected by aprox 15m TV coax. Would it be better to use twisted pair or
keep all the preamp up, close to the probe ?
73 de Luis

De: [email protected] [mailto:[email protected]] En nombre de DK7FC
Enviado el: martes, 02 de mayo de 2017 23:28
Para: [email protected]
Asunto: Re: LF: SL settings for EbNaut FFT recording ?

Hi Luis,

Am 02.05.2017 22:51, schrieb VIGILANT Luis Fernández:
The grabber is now showing full spectrum from 0-24KHz
OK. There is still some room for improvements :-)

The Rx is not at Benidorm in the high tower. It is in the roof of a two level house on top of a 5m pole
But clear out from high obstacles and trees
On top of a 5m pole is very good. But the location or earth is very contaminated.
The pole is a 50cm x 10mm diameter aluminium rod. Will play with the 10MOhm resistor and first fet stage
with filter.
I think this is not necessary now. Better to try to find a cleaner ground and/or location, as you say.
The noise at MiniWhip rised 20dB, so must get it
appart to keep the ear at MF/LF.
Yes, LF and MF stays important too! :-)
The power supply is a 12V transformer shared with the MiniWhip
Maybe this causes a ground loop which picks up the hum. Could explain why LF/MF became worse as well.
Will test another one just for the VLF probe and with better filtering.
Or try a battery in a first step and see the difference. A separate small transformer supply is certainly a good decision.
The GND of the antenna is separated
from mains earth and there is an audio transformer to the PC soundcard
BTW. What I'm getting from SL is one FFT file 112Kb size every hour as Markus said
But how can I merge all the files of a 8h transmission like the one your are running now ?
Each file covers 8.9 hours. They are just overlapping so that you can select the closest one (lowest start time offset). I don't know the exact settings though. I would recommend to set the FFT center frequency to 8270.1 Hz.

Your signal in your grabber looks stronger than the previous transmissions
It is the same antenna current though.

73, Stefan
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