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LF: RE: Some improvements in VLF Rx

To: <[email protected]>
Subject: LF: RE: Some improvements in VLF Rx
From: "Clemens Paul" <[email protected]>
Date: Mon, 8 May 2017 14:40:27 +0200
In-reply-to: <[email protected]cal>
References: <[email protected]> <[email protected]cal>
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Thread-index: AQHSx9kqLov3ejSO8ky0ZlWew2jd+6HqXfnA
Hi Luis,

>Would it be better to use twisted pair

At this low QRG skin depth may become an issue.
The coax shield might be not thick enough.
So it's probably worth a try with twisted pair.

73
Clemens
DL4RAJ 


>-----Original Message-----
>From: [email protected] 
>[mailto:[email protected]] On Behalf Of 
>VIGILANT Luis Fernández
>Sent: Monday, May 08, 2017 10:58 AM
>To: [email protected]
>Subject: LF: Some improvements in VLF Rx
>
>Hi VLF
> 
>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
>https://ea5dom.ure.es/grabber/index.html
> 
>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
>EA5DOM
>________________________________
>
>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 
>       https://ea5dom.ure.es/grabber/index.html
>
>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
>
>FB. 
>
>       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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